CHAPTER IV

HYMENOPTERA ACULEATA _CONTINUED_—DIVISION IV. FORMICIDAE OR ANTS

DIVISION IV. HETEROGYNA OR FORMICIDAE—ANTS.

_The segment, or the two segments, behind the propodeum, either small or of irregular form, so that if not throughout of small diameter, the articulation with the segment behind is slender, and there is great mobility. The trochanters undivided. The individuals of each species are usually of three kinds, males, females and workers; the latter have no wings, but the males and females are usually winged, though the females soon lose the flying organs. They live in communities of various numbers, the majority being workers. The larvae are helpless maggots fed and tended by the workers or by the female._

[Illustration: Fig. 53—Abdomens of ants. A, Of _Camponotus rubripes_ (Formicides); B, of _Ectatomma auratum_ (Ponerides); C, of _Aphaenogaster barbara_ (Myrmicides). _a_, Propodeum; _b_, first abdominal segment forming a scale or node; _c_, second; _d_, third abdominal segment.]

In ants the distinction between the three great regions of the body is very marked. The abdomen is connected with the propodeum in a peculiar manner, one or two segments being detached from the main mass to form a very mobile articulation. This is the most distinctive of the characters of ants. The structure and form of these parts varies {132}greatly in the family: and the Amblyoponides do not differ in a marked manner from the Scoliidae in fossorial Hymenoptera.

[Illustration: Fig. 54—Front of head of _Dinoponera grandis_. A, Mouth closed; B, open.]

The arrangement of the parts of the mouth is remarkable, and results in leaving the mandibles quite free and unconnected with the other trophi; the mouth itself is, except during feeding, closed completely by the lower lip and maxilla assuming an ascending vertical direction, while the upper lip hangs down and overlaps the lower lip, being closely applied to it; so that in Ponerides the palpi, except the apices of the maxillary pair, are enclosed between the upper and lower lips (Fig. 54, A). In Cryptocerini the palpi are not covered by the closed lips, but are protected by being placed in chinks at the outsides of the parts closing the mouth. The mandibles of ants can thus be used in the freest manner without the other parts of the mouth being opened or even moved. The mandibles close transversely over the rest of the mouth, and when shut are very firmly locked. There are, however, some ants in which the lips remain in the position usual in mandibulate Insects.

The antennae, except in the males of some species, have a long basal joint and are abruptly elbowed at its extremity. The eyes and ocelli vary excessively, and may be totally absent or very highly developed in the same species. The winged forms are, however, never blind. The size of the head varies extremely in the same species; it is frequently very small in the males, and largest in the workers. In some ants the worker-caste consists of large-headed and small-headed individuals; the former are called soldiers, and it has been supposed that some of them may act the part of superior officers to the others. It should be clearly understood that there is no definite distinction between soldiers and workers; so that in this respect they are widely different from Termites.

{133}[Illustration: Fig. 55—_Oecodoma cephalotes._ South America. A, Worker major; B, female after casting the wings.]

[Illustration: Fig. 56.—Stridulating organ of an ant, _Myrmica rubra_, var. _laevinodis_. Sagittal section of part of the 6th and 7th post-cephalic segments. (After Janet.) _a_, _a^1_, muscles; _b_, connecting membrane (corrugated) between 6th and 7th segments: _c_, 6th segment; _d_, its edge or scraper; _e_, striate area, or file on 7th segment; _f_, posterior part of 7th segment; _g_, cells, inside body; _h_, trachea.]

The complex mass forming the thorax is subject to great change of structure in the same species, according as the individuals are winged or wingless. The sutures between the dorsal (notal) pieces are frequently obliterated in the workers, while they are distinct in the males and females, and the pieces themselves are also much larger in size in these sexed individuals. The pro-mesothoracic stigma is apparently always distinct; the meso-metathoracic one is distinct in the male _Dorylus_, but can scarcely be detected in the winged forms of other ants, owing to its being enclosed within, and covered by, the suture between the two segments: in the workers, however, it is usually quite conspicuous. The posterior part of the thoracic mass, the propodeum or median segment, is of considerable size; no transverse suture between the component pieces of this part can be seen, but its stigma is always very distinct. The peduncle, or pedicel, formed by the extremely mobile segment or segments at the base of the abdomen (already noticed as forming the most conspicuous character of the family), exhibits much variety. Sometimes the first segment bears a plate or shield called a scale (Fig. 53, A, _b_); at other times there are two {134}small segments (Fig. 53, B, C, _b_, _c_) forming nodes or knots, of almost any shape. The articulations between these segments are of the most perfect description. In many ants these parts bear highly developed stridulating organs, and the delicacy and perfection of the articulations allow the parts to be moved either with or without producing stridulation. In the male sex the peduncle and its nodes are much less perfect, and possess comparatively little capacity for movement; in the male of _Dorylus_ (Figs. 79, A, and 80, _f_) the single node is only imperfectly formed. The eyes and ocelli of the males are usually more largely developed than they are in the female, though the head is much smaller.

The legs of ants are elongate, except in a few forms; the Cryptocerini and the males of Dorylides being the most conspicuous exceptions. The tarsi are five-jointed, the basal joint being disproportionately elongate, so that in use it acts in many species as if it were a portion of the tibia, the other four joints forming the functional foot. The front tibiae are furnished with a beautiful combing apparatus (Fig. 57).

[Illustration: Fig. 57.—Combs and brushes on front leg of an ant, _Dinoponera grandis_ (tip of tibia, bearing the comb-like spur, and the base of the first joint of the tarsus; cf. fig. 75). A, Inner, B, outer aspect.]

FEATURES OF ANT-LIFE.—In order that the reader may realise the nature of ant-life we may briefly recount its more usual and general features. Numerous eggs are produced in a nest by one or more queens, and are taken care of by workers. These eggs hatch and produce helpless maggots, of which great care is taken by the workers. These nurses feed their charges from their own mouths, and keep the helpless creatures in a fitting state by transporting them to various chambers in conformity with changes of temperature, humidity, and so on. When full grown the maggots change to pupae. In some species the maggots form cocoons for themselves, but in others this is not the case, and the pupae are naked.[54] After a brief period of {135}pupal life a metamorphosis into the perfect Insect occurs. The creatures then disclosed may be either winged or wingless; the wingless are the workers and soldiers—imperfect females—the winged are males or females fully developed. The workers remain in or near the nest they were produced in, but the winged individuals rise into the air for a nuptial flight, often in great numbers, and couple. When this is accomplished the male speedily dies, but the females cast their wings and are ready to enter on a long life devoted to the production of eggs. From this account it will be gathered that males are only found in the nests for a very short time; the great communities consisting at other periods entirely of the two kinds of females and of young. The imperfect females are themselves in some species of various kinds; each kind being restricted, more or less completely, to a distinct kind of duty.

No Insects are more familiar to us than ants; in warm countries some of them even invade the habitations of man, or establish their communities in immediate proximity to his dwellings. Their industry and pertinacity have, even in remote ages, attracted the attention and admiration of serious men; some of whom—we need scarcely mention Solomon as amongst them—have not hesitated to point out these little creatures as worthy of imitation by that most self-complacent of all the species of animals, _Homo sapiens_.

Observation has revealed most remarkable phenomena in the lives of these Insects. Indeed, we can scarcely avoid the conclusion that they have acquired in many respects the art of living together in societies more perfectly than our own species has, and that they have anticipated us in the acquisition of some of the industries and arts that greatly facilitate social life. The lives of individual ants extend over a considerable number of years—in the case of certain species at any rate—so that the competence of the individual may be developed to a considerable extent by exercise; and one generation may communicate to a younger one by example the arts of living by which it has itself profited. The prolonged life of ants, their existence in the perfect state at all seasons, and the highly social life they lead are facts of the greatest biological importance, and are those that we should expect to be accompanied by greater and wider competence than is usually exhibited {136}by Insects. There can indeed be little doubt that ants are really not only the "highest" structurally or mechanically of all Insects, but also the most efficient. There is an American saying to the effect that the ant is the ruler of Brazil. We must add a word of qualification; the competence of the ant is not like that of man. It is devoted to the welfare of the species rather than to that of the individual, which is, as it were, sacrificed or specialised for the benefit of the community. The distinctions between the sexes in their powers or capacities are astonishing, and those between the various forms of one sex are also great. The difference between different species is extreme; we have, in fact, the most imperfect forms of social evolution coexisting, even locally, with the most evolute.

These facts render it extremely difficult for us to appreciate the ant; the limitations of efficiency displayed by the individual being in some cases extreme, while observation seems to elicit contradictory facts. About two thousand species are already known, and it is pretty certain that the number will reach at least five thousand. Before passing to the consideration of a selection from what has been ascertained as to the varieties of form and of habits of ants we will deal briefly with their habitations and polymorphism, reserving some remarks as to their associations with other Insects to the conclusion of this chapter.

NESTS.—Ants differ greatly from the other Social Hymenoptera in the nature of their habitations. The social bees construct cells of wax crowded together in large numbers, and the wasps do the like with paper; the eggs and young being placed, each one in a separate cell, the combinations of which form a comb. Ants have, however, a totally different system; no comb is constructed, and the larvae are not placed in cells, but are kept in masses and are moved about from place to place as the necessities of temperature, air, humidity and other requirements prompt. The habitations of ants are in all cases irregular chambers, of which there is often a multiplicity connected by galleries, and they sometimes form a large system extending over a considerable area. Thus the habitations of ants are more like those of the Termites than those of their own allies among the Hymenoptera. They are chiefly remarkable for their great variety, and for the skilful manner in which they are adapted by their little artificers to

## particular conditions. The most usual form in Europe, is a {137}number of

subterranean chambers, often under the shelter of a stone, and connected by galleries. It is of course very difficult to trace exactly the details of such a work, because when excavations are made for the purposes of examination, the construction becomes destroyed; it is known, however, that some of these systems extend to a considerable depth in the earth, it is said to as much as nine feet, and it is thought the object of this is to have access to sufficiently moist earth, for ants are most sensitive to variations in the amount of moisture; a quite dry atmosphere is in the case of many species very speedily fatal. This system of underground labyrinths is sometimes accompanied by above-ground buildings consisting of earth more or less firmly cemented together by the ants; this sort of dwelling is most frequently adopted when the soil in which the nests are placed is sandy; it is probable that the earth is in such cases fastened together by means of a cement produced by the salivary glands of the ants, but this has not been determined with certainty; vaulted galleries or tunnels of this kind are constructed by many species of ants in order to enable them to approach desired objects.

[Illustration: Fig. 58—Portion of combined nest of _Formica fusca_ and _Solenopsis fugax_. (After Forel.) × ⅔. _f_, _f′_, Chambers of _Formica_, recognisable by the coarser shading; _s_, _s′_, chambers of the _Solenopsis_ (with finer shading); _s″_, opening in one of the chambers, the entrance to one of the galleries that connects the chambers of the Solenopsis; _w_, walls forming the foundations of the nest and the limits of the chambers.]

In South America _Camponotus rufipes_ and other species that habitually dwell in stumps, in certain districts where they are liable to inundations, build also nests of a different nature on trees for refuge during the floods. In Europe, a little robber-ant, _Solenopsis fugax_, constructs its dwelling in combination with that of _Formica fusca_ (Fig. 58), in such a manner that its chambers cannot, on account of the small size of the orifices, be entered by the much larger _Formica_. Hence the robber obtains an easy living at the expense of the larger species. The Sauba or Sauva ants of South America (the genus _Atta_ of some, _Oecodoma_ of other authors) appear to be most proficient in the art of {138}subterranean mining. Their systems of tunnels and nests are known to extend through many square yards of earth, and it is said on the authority of Hamlet Clark that one species tunnelled under the bed of the river Parahyba at a spot where it was as broad as the Thames at London Bridge.

A considerable number of ants, instead of mining in the ground, form chambers in wood; these are usually very close to one another, because, the space being limited, galleries cannot be indulged in. _Camponotus ligniperdus_ in Europe, and _C. pennsylvanicus_ in North America, work in this way.

Our British _Lasius fuliginosus_ lives in decayed wood. Its chambers are said by Forel to consist of a paper-like substance made from small fragments of wood. _Cryptocerus_ burrows in branches. _Colobopsis_ lives in a similar manner, and Forel informs us that a worker with a large head is kept stationed within the entrance, its great head acting as a stopper; when it sees a nest-fellow desirous of entering the nest, this animated and intelligent front-door then retreats a little so as to make room for ingress of the friend. Forel has observed that in the tropics of America a large number of species of ants live in the stems of grass. There is also quite a fauna of ants dwelling in hollow thorns, in spines, on trees or bushes, or in dried parts of pithy plants; and the tropics also furnish a number of species that make nests of delicate paper, or that spin together by means of silk the leaves of trees. One eastern species—_Polyrhachis spinigera_—fabricates a gauze-like web of silk, with which it lines a subterranean chamber after the manner of a trap-door spider.

[Illustration: Fig. 59—Ant-plant, _Hydnophytum montanum_. Java. (After Forel.)]

Some species of ants appear to find both food and shelter {139}entirely on the tree they inhabit, the food being usually sweet stuff secreted by glands of the plant. It is thought that the ants in return are of considerable benefit to the plant by defending it from various small enemies, and this kind of symbiosis has received much attention from naturalists. A very curious condition exists in the epiphytic plants of the genera _Myrmecodia_ and _Hydnophytum_; these plants form large bulb-like (Fig. 59) excrescences which, when cut into, are found to be divided into chambers quite similar to those frequently made by ants. Though these structures are usually actually inhabited by ants, it appears that they are really produced by the plant independent of the Insects.

VARIABILITY AND POLYMORPHISM OF ANTS.—Throughout the Hymenoptera there are scattered cases in which one of the sexes appears in dimorphic form. In the social kinds of bees and wasps the female sex exists in two conditions, a reproductive one called queen, and an infertile one called worker, the limits between the two forms seeming in some cases (honey-bee) to be absolute as regards certain structures. This sharp distinction in structure is rare; while as regards fertility intermediate conditions are numerous, and may indeed be induced by changing the social state of a community.[55] In ants the phenomena of the kind we are alluding to are very much more complex. There are no solitary ants; associations are the rule (we shall see there are one or two cases in which the association is with individuals of other species). In correlation with great proclivity to socialism we find an extraordinary increase in the variety of the forms of which species are made up. In addition to the male and female individuals of which the species of Insects usually consist, there are in ants workers of various kinds, and soldiers, all of which are modified infertile females. But in addition to the existence of these castes of infertile females, we find also numerous cases of variability or of dimorphism of the sexual individuals; and this in both sexes, though more usually in the female. Thus there exists in ants an extraordinary variety in the polymorphism of forms, as shown by the table on p. 141, where several very peculiar conditions are recorded.

The complex nature of these phenomena has only recently {140}become known, and as yet has been but little inquired into. The difference between the thoracic structure in the case of the winged and wingless females of certain species (Fig. 55, and in vol. v. fig. 339) is enormous, but in other species this difference appears to be much less. The ordinary distinctions between the queen-female and worker-females appear to be of two kinds; firstly, that the former is winged, the latter wingless;[56] and secondly, that the former possesses a _receptaculum seminis_, the latter does not. In a few cases it would seem that the dimorphism of winged and wingless forms is not complete, but that variability exists. Intermediate conditions between the winged and wingless forms are necessarily rare; nevertheless a certain number have already been detected, and specimens of _Lasius alienus_ have been found with short wings. In rather numerous species some or all of the fertile females depart from the usual state and have no wings; (a similar condition is seen, it will be recollected, in Mutillides and Thynnides of the neighbouring family Scoliidae). A dimorphism as regards wings also exists in the male sex, though it is only extremely rarely in ants that the males are wingless. Neverless a few species exist of which only wingless males have been found, and a few others in which both winged and wingless individuals of this sex are known to occur. The wingless males of course approach the ordinary workers (= infertile wingless females) in appearance, but there is not at present any reason for supposing that they show any diminution in their male sexual characters. The distinction between workers and females as based on the existence or non-existence of a _receptaculum seminis_ has only recently become known, and its importance cannot yet be estimated. The adult, sexually capable, though wingless forms, are called ergatoid, because they are similar to workers (Ἐργατης, a worker).[57]

{141}TABLE OF THE CHIEF FORMS OF POLYMORPHISM IN ANTS.

OW♂ = Ordinary Winged Male. E♂ = Ergatoid Male. OW♀ = Ordinary Winged Female. EF♀ = Ergatoid Fertile Female. I♀W = Intermediate between Female and Worker. Sol = Soldier. WMj = Worker Major. WMi = One or more kinds of Worker Minor. +———————————————————————————+———+———+———+———————+———————+———+—————+—————+ | Name of Ants. |OW♂|E♂ |OW♀| EF♀ | I♀W |Sol| WMj | WMi | +———————————————————————————+———+———+———+———————+———————+———+—————+—————+ | _Myrmica_, _Polyrhachis_, | + | | + | | | | + | | | etc. | | | | | | | | | | | | | | | | | | | | _Camponotus_, _Atta_, | + | | + | | | | + | + | | Pheidologeton_, etc. | | | | | | | | | | | | | | | | | | | | _Pheidole_, subg. | + | | + | | | + | | + | | Colobopsis_ | | | | | | | | | | | | | | | | | | | | _Eciton hamatum_, | | | | | | | | | | E. quadriglume_, | + | | | + | | + | + | + | | E. foreli_, etc. | | | | | | | | | | | | | | | | | | | | _Cryptocerus_ | + | | + | | | + | + | + | | discocephalus_, etc. | | | | | | | | | | | | | | | | | | | | _Strongylognathus_ | + | | + | | | + | | | | | | | | | | | | | | _Carebara_ and | | | | | | | | | | Solenopsis_ (except | + | | + | | | | | + | | S. germinata_) | | | | | | | | | | | | | | | | | | | | _Solenopsis geminata_ | + | | + | | | | + | + | | | | | | | | | | | | _Formica rufa_ | + | | + | | + | | | | | | | | | |except-| | | | | | | | | |ionally| | | | | | | | | | | | | | | _Ponera punctatissima_ | + | + | + | | | | + | | | | | | | | | | | | | _Ponera ergatandria_ | ? | + | + | | | | + | | | | | | | | | | | | | _Cardiocondyla emeryi_ | + | | + | + | | | + | | | | | | | | | | | | | _C. wroughtonii_ and | | + | + | | | | + | | | C. stambuloffi_ | | | | | | | | | | | | | | | | | | | | _Formicoxenus nitidulus_ | | + | + | | | | + | | | | | | | | | | | | | _Tomognathus_ | + | | | + | | | | | | | | | | | | | | | | _Odontomachus haematodes_ | + | | + | + | | | + | | | | | | |except-| | | | | | | | | |ionally| | | | | | | | | | | | | | | | _Polyergus_ | + | | + | + | | | | | | | | | | | | | | | | _Dorylus_, _Anomma_, | + | | | + | | | + | + | | Eciton_ part. | | | | | | | | | | | | | | | | | | | | _Aenictus_ | + | | | | | | | + | | | | | | | | | | | | _Leptogenys_, _Diacamma_ | + | | | + | + | | + | | | | | | | | | | | | | _Myrmecocystus melliger_, | + | | + | | | | + | | | M. mexicanus_ | | | | | | | and | + | | | | | | | | |honey| | | | | | | | | |-pots| | | | | | | | | | | | | | | | | | | | + | + | | _Ponera eduardi_ | + | | + | | | |eyes |eyes | | | | | | | | |large|obso-| | | | | | | | | |lete | | | | | | | | | | | | _Anergates_ | | + | + | | | | | | +———————————————————————————+———+———+———+———————+———————+———+—————+—————+

In addition to the above there are apparently cases of females with post-metamorphic growth in Dorylides, but these have not yet been the subject of investigation.

{142}Much has been written about the mode in which the variety of forms of a single species of ant is produced. As to this there exists but little actual observation or experiment, and the subject has been much complicated by the anxiety of the writers to display the facts in a manner that will support some general theory. Dewitz was of opinion that workers and queens of ants were produced from different kinds of eggs. This view finds but little support among recent writers. Hart in recording the results of his observations on the parasol ant (of the genus _Atta_)—one of the species in which polymorphism is greatest—says[58] that these observations prove that "ants can manufacture at will, male, female, soldier, worker or nurse," but he has not determined the method of production, and he doubts it being "the character of the food." There is, however, a considerable body of evidence suggesting that the quality or quantity of the food, or both combined, are important factors in the treatment by which the differences are produced. The fact that the social Insects in which the phenomena of caste or polymorphism occur, though belonging to very diverse groups, all feed their young, is of itself very suggestive. When we add to this the fact that in ants, where the phenomena of polymorphism reach their highest complexity, the food is elaborated in their own organs by the feeders that administer it, it appears probable that the means of producing the diversity may be found herein. Wasmann has pointed out that the ants'-nest beetle, _Lomechusa_, takes much food from the ants, and itself destroys their young, and that in nests where _Lomechusa_ is abundant a large percentage of ergatogynous forms of the ants are produced. He attributes this to the fact that the destruction of the larvae of the ant by the beetle brings into play the instinct of the ants, which seek to atone for the destruction by endeavouring to produce an increased number of fertile forms; many ergatogynous individuals being the result. This may or may not be the case, but it is clear that the ants' instinct cannot operate without some material means, and his observation adds to the probability that this means is the food supply, modified either qualitatively or quantitatively.

The existence of these polymorphic forms led Herbert Spencer to argue that the form of an animal is not absolutely {143}determined by those "Anlagen" or rudiments that Weismann and his school consider to be all important in determining the nature or form of the individual, for if this were the case, how can it be, he asked, that one egg may produce either a worker, nurse, soldier or female ant? To this Wasmann (who continued the discussion) replied by postulating the existence of double, triple or numerous rudiments in each egg, the treatment the egg receives merely determining which of these rudiments shall undergo development.[59] Forel seems to have adopted this explanation as being the most simple. The probability of Weismann's hypothesis being correct is much diminished by the fact that the limit between the castes is by no means absolute. In many species intermediate forms are common, and even in those in which the castes are believed to be quite distinct, intermediate forms occur as very rare exceptions.[60] Emery accounts[61] for the polymorphism, without the assistance of the Weismannian hypothetical compound rudiments, by another set of assumptions; viz. that the phenomenon has been gradually acquired by numerous species, and that we see it in various stages of development; also that variation in nutrition does not affect all the parts of the body equally, but may be such as to carry on the development of certain portions of the organisation while that of other parts is arrested. Speaking broadly we may accept this view as consistent with what we know to be the case in other Insects, and with the phenomena of post-embryonic development in the class. But it must be admitted that our knowledge is at present quite inadequate to justify the formulation of any final conclusions.

The geological record of Formicidae is not quite what we should have expected. They are amongst the earliest Hymenoptera; remains referred to the family have been found in the Lias of Switzerland and in the English Purbecks. In Tertiary times Formicidae appear to have been about the most abundant of all Insects. At Florissant they occur in thousands and form in individuals about one-fourth of all the Insects found there. They have also been met with numerously in the European Tertiaries, and Mayr studied no less than 1500 specimens found {144}in amber. Formicides and Myrmicides are more abundant than Ponerides, but this latter group has the larger proportion of extinct genera; conditions but little dissimilar to those existing at present.

CLASSIFICATION OF ANTS.—Ants are considered by many entomologists to form a series called Heterogyna. They can, however, be scarcely considered as more than a single family, Formicidae, so that the serial name is superfluous. Their nearest approach to other Aculeates is apparently made, by _Amblyopone_, to certain Mutillides (_e.g._ _Apterogyna_) and to the Thynnides, two divisions of Scoliidae. Emery considers Dorylides rather than Amblyoponides to be the most primitive form of ants, but we are disposed to consider Forel's view to the effect we have above mentioned as more probably correct. The point is, however, very doubtful. The condition of the peduncle is in both the sub-families we have mentioned very imperfect compared with that of other ants. Both these sub-families are of very small extent and very imperfectly known. We shall also follow Forel in adopting six sub-families, Camponotides, Dolichoderides, Myrmicides, Ponerides, Dorylides, and Amblyoponides. Emery rejects the Amblyoponides as being merely a division of the Ponerides. This latter group displays the widest relations of all the sub-families, and may be looked on as a sort of central form. The Camponotides and Dolichoderides are closely allied, and represent the highest differentiation of the families in one direction. The Myrmicides are also highly differentiated, but are not allied to the Camponotides and Dolichoderides.[62]

SUB-FAM. 1. CAMPONOTIDES.—_Hind body furnished with but one constriction, so that only a single scale or node exists on the pedicel. Poison-sac forming a cushion of convolutions, on which is situate the modified sting, which forms merely an ejaculatory orifice for the poison._

The members of this very extensive division of ants can be readily distinguished from all others, except the Dolichoderides, by the absence of a true sting, and by the peculiar form of the hind body; this possesses only a single scale at the base, and has no {145}constriction at all on the oval, convex and compact mass of the abdomen behind this. The cloacal orifice is circular, not, as in other ants, transverse. These characters are accompanied by a difference in habits. The Camponotides, though they do not sting, produce poison in large quantity, and eject it to some distance. Hence, if two specimens are confined in a tube they are apt to kill one another by the random discharges they make. Janet suggests that in order to neutralise the effect of this very acid poison, they may have some means of using, when they are in their natural abodes, the alkaline contents of a second gland with which they are provided. We shall mention the characters by which the Camponotides are distinguished from the small sub-family Dolichoderides when we deal with the latter.

The sub-family includes 800 or more species. _Camponotus_ itself is one of the most numerous in species of all the genera of Formicidae, and is distributed over most parts of the earth. We have no species of it in Britain, but in the south of Europe the _Camponotus_ become very conspicuous, and may be seen almost everywhere stalking about, after the fashion of our British wood-ant, _Formica rufa_, which in general appearance _Camponotus_ much resembles.

Until recently, the manner in which fresh nests of ants were founded was unknown. In established nests the queen-ant is fed and tended by the workers, and the care of the helpless larvae and pupae also devolves entirely on the workers, so that the queens are relieved of all functions except that of producing eggs. It seemed therefore impossible that a fresh nest could be established by a single female ant unless she were assisted by workers. The mode in which nests are founded has, however, been recently demonstrated by the observations of Lubbock, M‘Cook, Adlerz, and more

## particularly by those of Blochmann, who was successful in observing the

formation of new nests by _Camponotus ligniperdus_ at Heidelberg. He found under stones in the spring many examples of females, either solitary or accompanied only by a few eggs, larvae or pupae. Further, he was successful in getting isolated females to commence nesting in confinement, and observed that the ant that afterwards becomes the queen, at first carries out by herself all the duties of the nest: beginning by making a small burrow, she lays some eggs, and when these hatch, feeds and tends the larvae and pupae; the first specimens of these {146}latter that become perfect Insects are workers of all sizes, and at once undertake the duties of tending the young and feeding the mother, who, being thus freed from the duties of nursing and of providing food while she is herself tended and fed, becomes a true queen-ant. Thus it seems established that in the case of this species the division of labour found in the complex community, does not at first exist, but is correlative with increasing numbers of the society. Further observations as to the growth of one of these nascent communities, and the times and conditions under which the various forms of individuals composing a complete society first appear, would be of considerable interest.

An American species of the same genus, _C. pennsylvanicus_, the carpenter-ant, establishes its nests in the stumps of trees. Leidy observed that solitary females constructed for themselves cells in the wood and closed the entrances, and that each one in its solitary confinement reared a small brood of larvae. The first young produced in this case are said to be of the dwarf caste, and it was thought by the observer that the ant remained not only without assistance but also without food during a period of some weeks, and this although she was herself giving food to the larvae she was rearing.

Adlerz states that the females or young queens take no food while engaged in doing their early work, and that the large quantity of fat-body they possess enables them to undergo several months of hunger. In order to feed the young larvae they use their own eggs or even the younger larvae. It is to the small quantity of food rather than to its nature that he attributes the small size of the first brood of perfect workers. M. Janet[63] has recently designed an ingenious and simple apparatus for keeping ants in captivity. In one of these he placed a solitary female of _Lasius alienus_, unaccompanied by any workers or other assistants, and he found at the end of 98 days that she was taking care of a progeny consisting of 50 eggs, 2 larvae, 5 pupae in cocoons, 5 without cocoons. On the 102nd day workers began to emerge from the cocoons.[64] From these observations it is evident that the queen-ant, when she begins her nest, lives under conditions extremely different from those of the royal state she afterwards reaches.

{147}In many kinds of ants the full-grown individuals are known to feed not only the larvae by disgorging food from their own mouths into those of the little grubs, but also to feed one another. This has been repeatedly observed, and Forel made the fact the subject of experiment in the case of _Camponotus ligniperdus_. He took some specimens and shut them up without food for several days, and thereafter supplied some of them with honey, stained with Prussian blue; being very hungry, they fed so greedily on this that in a few hours their hind bodies were distended to three times their previous size. He then took one of these gorged individuals and placed it amongst those that had not been fed. The replete ant was at once explored by the touches of the other ants and surrounded, and food was begged from it. It responded to the demands by feeding copiously a small specimen from its mouth: when this little one had received a good supply, it in turn communicated some thereof to other specimens, while the original well-fed one also supplied others, and thus the food was speedily distributed. This habit of receiving and giving food is of the greatest importance in the life-history of ants, and appears to be the basis of some of the associations that, as we shall subsequently see, are formed with ants by numerous other Insects.

[Illustration: Fig. 60—_Oecophylla smaragdina._ Worker using a larva for spinning.]

_Oecophylla smaragdina_, a common ant in Eastern Asia, forms shelters on the leaves of trees by curling the edges of leaves and joining them together. In doing this it makes use of an expedient that would not be believed had it not been testified by several competent and independent witnesses. The perfect ant has no material with which to fasten together the edges it curls; its larva, however, possesses glands that secrete a supply of material for it to form a cocoon with, and the ants utilise the larvae to effect their purpose. Several of them combine to hold the foliage in the desired position, and while they do so, other ants come up, each one of which carries a larva in its jaws, applies the mouth of the larva to the parts where the cement is required, and makes it disgorge the sticky {148}material. Our figure is taken from a specimen (for which we are indebted to Mr. E. E. Green) that was captured in the act of bearing a larva.

_Formica rufa_, the Red-ant, Wood-ant, or Hill-ant, is in this country one of the best-known members of the Formicidae. It frequents woods, especially such as are composed, in whole or part, of conifers, where it forms large mounds of small sticks, straws, portions of leaves, and similar material. Although at first sight such a nest may appear to be a chaotic agglomeration, yet examination reveals that it is arranged so as to leave many spaces, and is penetrated by galleries ramifying throughout its structure. These mound-nests attain a considerable size when the operations of the industrious creatures are not interfered with, or their work destroyed, as it too often is, by ignorant or mischievous persons. They may reach a height of three feet or near it, and a diameter of twice that extent. The galleries by which the heaps are penetrated lead down to the earth below. From the mounds extend in various directions paths constantly traversed by the indefatigable ants. M‘Cook observed such paths in the Trossachs; they proceed towards the objects aimed at in lines so straight that he considers they must be the result of some sense of direction possessed by the ants; as it is impossible to suppose they could perceive by the sense of sight the distant objects towards which the paths were directed: these objects in the case M‘Cook describes were oak-trees up which the ants ascended in search of Aphides.

M‘Cook further observed that one of the oak-trees was reached by individuals from another nest, and that each of the two parties was limited to its own side of the tree, sentinels being placed on the limits to prevent the trespassing of an intruder; he also noticed that the ants saw an object when the distance became reduced to about an inch and a half from them. This species is considered to be wanting in individual courage; but when acting in combination of vast numbers it does so with intelligence and success. It does not make slaves, but it has been observed by Bignell and others that it sometimes recruits its numbers by kidnapping individuals from other colonies of its own species. Its nests are inhabited by forty or fifty species of guests of various kinds, but chiefly Insects. Another ant, _Myrmica laevinodis_, sometimes lives with it in perfect harmony, and _Formicoxenus {149}nitidulus_ lives only with _F. rufa_. Amongst the most peculiar of its dependants we may mention large beetles of the genera _Cetonia_ and _Clythra_, which in their larval state live in the hills of the wood-ant. It is probable that they subsist on some of the vegetable matter of which the mounds are formed. Adlerz has given some attention to the division of labour amongst the different forms of the workers of ants, and says that in _F. rufa_ it is only the bigger workers that carry building and other materials, the smaller individuals being specially occupied in the discovery of honey-dew and other Aphid products. In _Camponotus_ it would appear, on the other hand, that the big individuals leave the heavy work to be performed by their smaller fellows.

The wood-ant and its near allies have been, and indeed still are, a source of great difficulty to systematists on account of the variation that occurs in the same species, and because this differs according to locality. Our European _F. rufa_ has been supposed to inhabit North America, and the interesting accounts published by M‘Cook of the mound-making ant of the Alleghanies were considered to refer to it. This Insect, however, is not _F. rufa_, as was supposed by M‘Cook, but _F. exsectoides_, Forel. It forms colonies of enormous extent, and including an almost incredible number of individuals. In one district of about fifty acres there was an Ant City containing no less than 1700 of these large ant-hills, each one teeming with life. It was found by transferring ants from one hill to another that no hostility whatever existed between the denizens of different hills; the specimens placed on a strange hill entered it without the least hesitation. Its habits differ in some particulars from those of its European congener; the North American Insect does not close the formicary at night, and the inquilines found in its nest are very different from those that live with _F. rufa_ in Europe. Whether the typical wood-ant occurs in North America is doubtful, but there are races there that doubtless belong to the species.

_F. sanguinea_ is very similar in appearance to its commoner congener _F. rufa_, and is the only slave-making ant we possess in Britain. This species constructs its galleries in banks, and is of very courageous character, carrying out its military operations with much tactical ability. It is perfectly able to live without the assistance of slaves, and very frequently does so; indeed it {150}has been asserted that it is in our own islands (where, however, it is comparatively rare) less of a slave-owner than it is in Southern Europe, but this conclusion is very doubtful. It appears when fighting to be rather desirous of conquering its opponents by inspiring terror and making them aware of its superiority than by killing them; having gained a victory it will carry off the pupae from the nest it has conquered to its own abode, and the ants of the stranger-species that develop from these pupae serve the conquerors faithfully, and relieve them of much of their domestic duties. The species that _F. sanguinea_ utilises in this way in England are _F. fusca_, _F. cunicularia_, and possibly _Lasius flavus_. Huber and Forel have given graphic accounts of the expeditions of this soldier-ant. In the mixed colonies of _F. sanguinea_ and _F. fusca_ the slaves do most of the house-work, and are more skilful at it than their masters. Adlerz says that one of the slaves will accomplish twice as much work of excavation in the same time as the slave-owner; these latter being lazy and fond of enjoyment, while the slaves are very industrious.

[Illustration: Fig. 61—Head of _Polyergus rufescens_. (After André.)]

_Polyergus rufescens_, an European ant allied to _Formica_, is renowned since the time of Huber (1810) as the slave-making or Amazon ant. This creature is absolutely dependent on its auxiliaries for its existence, and will starve, it is said, in the midst of food unless its servitors are there to feed it. Wasmann, however, states that _Polyergus_ does possess the power of feeding itself to a certain extent. Be this as it may, the qualities of this ant as warrior are superb. When an individual is fighting alone its audacity is splendid, and it will yield to no superiority of numbers; when the creatures are acting as part of an army the individual boldness gives place to courage of a more suitable sort, the ants then exhibiting the act of retreating or making flank movements when necessary. If a _Polyergus_ that is acting as a member of a troop finds itself isolated, and in danger of being overpowered, it has then no hesitation in seeking safety even by flight. This species is provided with mandibles of a peculiar nature; they are not armed with teeth, {151}but are pointed and curved; they are therefore used after the manner of poignards, and when the ant attacks a foe it seizes the head between the points of these curved mandibles, and driving them with great force into the brain instantly paralyses the victim.

Mandibles of this shape are evidently unfitted for the purposes of general work, they can neither cut, crush, nor saw, and it is not impossible that in their peculiar shape is to be found the origin of the peculiar life of _Polyergus_: we find similar mandibles reappearing amongst the aberrant Dorylides, and attaining a maximum of development in the ferocious _Eciton_; they also occur, or something like them, in a few aberrant Myrmicides; and in the male sex of many other ants, which sex exercises no industrial arts, this sort of mandible is present.

The ants that _Polyergus_ usually attacks in order to procure slaves are _Formica fusca_ and _F. fusca_, race _auricularia_; after it has routed a colony of one of these species, _P. rufescens_ pillages the nest and carries off pupae and some of the larger larvae to its own abode. When the captives thus deported assume the imago state, they are said to commence working just as if they were in their own houses among their brothers and sisters, and they tend their captors as faithfully as if these were their own relatives: possibly they do not recognise that they are in unnatural conditions, and may be quite as happy as if they had never been enslaved. The servitors are by no means deficient in courage, and if the place of their enforced abode should be attacked by other ant-enemies they defend it bravely. The fact that _P. rufescens_ does not feed its larvae has been considered evidence of moral degeneration, but it is quite possible that the Insect may be unable to do so on account of some deficiency in the mouth-parts, or other similar cause. The larvae of ants are fed by nutriment regurgitated from the crop of a worker (or female), and applied to the excessively minute mouth of the helpless grub: for so delicate a process to be successfully accomplished, it is evident that a highly elaborated and specialised arrangement of the mouth-parts must exist, and it is by no means improbable that the capacity of feeding its young in true ant-fashion is absent in _Polyergus_ for purely mechanical reasons.

M‘Cook states that the North American ant, _Polyergus lucidus_, which some entomologists consider to be merely a variety of {152}the European species, makes slaves of _Formica schaufussi_, itself does no work, and partakes of food only when fed by its servitors. He did not, however, actually witness the process of feeding. When a migration takes place the servitors deport both the males and females of _P. lucidus_. M‘Cook adds that the servitors appear to be really mistresses of the situation, though they avail themselves of their power only by working for the advantage of the other species.

[Illustration: Fig. 62—_Myrmecocystus mexicanus._ Honey-pot ant, dorsal view.]

[Illustration: Fig. 63—_Myrmecocystus mexicanus._ Lateral view.]

The honey-ant of the United States and Mexico has been investigated by M‘Cook and others; the chief peculiarity of the species is that certain individuals are charged with a sort of honey till they become enormously distended, and in fact serve as leather bottles for the storage of the fluid. The species _Myrmecocystus hortideorum_ and _M. melliger_, are moderate-sized Insects of subterranean habits, the entrance to the nest of _M. hortideorum_ being placed in a small raised mound. The honey is the product of a small gall found on oak leaves, and is obtained by the worker-ants during nocturnal expeditions, from which they return much distended; they feed such workers left at home as may be hungry, and then apparently communicate the remainder of the sweet stuff they have brought back to already partly charged "honey-bearers" left in the nest. The details of the process have not been observed, but the result is that the abdomens of the bearers become distended to an enormous extent (Figs. 62, 63), and the creatures move but little, and remain suspended to the roof of a special chamber. It is considered by M‘Cook that these living honey-tubs preserve the food till a time when it is required for the purposes of feeding the community. The distension is produced entirely by the overcharging of the honey-crop, the other contents of the abdomen being {153}forced by the distention to the posterior part of the body. Lubbock has since described an Australian ant, _Melophorus inflatus_, having a similar peculiar habit, but belonging to the allied tribe Plagiolepisii. Quite recently a South African honey-tub ant belonging to the distinct genus _Plagiolepis_ (_Ptrimeni_ For.) has been discovered, affording a proof that an extremely specialised habit may arise independently of relation between the Insects, and in very different parts of the world.

Species of the genus _Lasius_ are amongst the most abundant of the ant-tribe in Britain. They are remarkable for their constructive powers. _L. niger_, the common little black garden-ant, forms extensive subterranean galleries, and is extremely successful in the cultivation of various forms of Aphidae, from the products of which the species derives a large part of its subsistence. The ants even transport the Aphidae to suitable situations, and thus increase their stock of this sugary kind of cattle, and are said to take the eggs into their own dwellings in the autumn so that these minute and fragile objects may be kept safe from the storms and rigours of winter. These little creatures are brave, but when attacked by other ants they defend themselves chiefly by staying in their extensive subterranean galleries, and blocking up and securing these against their assailants.

_L. fuliginosus_, another of our British species, has very different habits, preferring old trees and stumps for its habitation; in the hollows of these it forms dwellings of a sort of card; this it makes from the mixture of the secretions of its salivary glands with comminuted fragments of wood, after the fashion of wasps. It is a moderate-sized ant, much larger than the little _L. niger_, and is of a black colour and remarkably shining; it gives off a very strong but by no means disagreeable odour, and may be seen on the hollow trees it frequents, stalking about in large numbers in a slow and aimless manner that contrasts strikingly with the

## active, bustling movements of so many of its congeners. When this species

finds suitable trees near one another, a colony is established in each; the number of individuals thus associated becomes very large, and as the different colonies keep up intercommunication, this habit is very useful for purposes of defence. Forel relates that he once brought a very large number of _Formica pratensis_ and liberated them at the base of a tree in which was a nest of _L. fuliginosus_; these latter, finding {154}themselves thus assaulted and besieged, communicated in some way, information of the fact to the neighbouring colonies, and Forel soon saw large columns of the black creatures issuing from the trees near by and coming with their measured paces to the assistance of their _confrères_, so that the invaders were soon discomfited and destroyed. Although the European and North American representatives of the sub-family Camponotides live together in assemblies comprising as a rule a great number of individuals, and although the separate nests or formicaries which have their origin from the natural increase of a single original nest keep up by some means a connection between the members, and so form a colony of nests whose inhabitants live together on amicable terms, yet there is no definite information as to how long such association lasts, as to what is the nature of the ties that connect the members of the different nests, nor as to the means by which the colonies become dissociated. It is known that individual nests last a long time. Charles Darwin has mentioned in a letter to Forel that an old man of eighty told him he had noticed one very large nest of _Formica rufa_ in the same place ever since he was a boy. But what period they usually endure is not known, and all these points probably vary greatly according to the species concerned. It has been well ascertained that when some ants find their nests, for some unknown reason, to be unsuitable the inhabitants leave their abodes, carrying with them their young and immature forms, and being accompanied or followed by the various parasites or commensals that are living with them. Wasmann and other entomologists have observed that the ants carry bodily some of their favourite beetle-companions, as well as members of their own species. Forel observed that after a nest of _Formica pratensis_ had been separated into two nests placed at a considerable distance from one another so as to have no intercommunication, the members yet recognised one another as parts of the same family after the lapse of more than a month; but another observation showed that after some years of separation they were no longer so recognised.

Although it is now well ascertained that ants are able to distinguish the individuals belonging to their own nests and colonies from those that, though of their own species, are not so related to them, yet it is not known by what means the recognition is effected; there is, however, some reason to suppose that it {155}is by something of the nature of odour. One observer has noticed that if an ant fall into water it is on emerging at first treated as if it were a stranger by its own friends; but other naturalists have found this not to be the case in other species. Contact with corrosive sublimate deprives ants for a time of this power of recognising friends, and under its influence they attack one another in the most ferocious mariner.

The nests and colonies of the species of Camponotides we have considered are all constructed by societies comprising a great number of individuals; there are, however, in the tropics numerous species that form their nests on foliage, and some of these contain only a few individuals. The leaf-nests (Fig. 64) of certain species of _Polyrhachis_ are said to be formed of a paper-like material, and to contain each a female and about 8 or 10 worker ants. Forel[65] has examined nests of several Indian species, and finds they differ from those of other ants in consisting of a single cavity, lined with silk like that of a spider. These nests are further said to be constructed so as to render them either inconspicuous or like other objects on the leaves; _P. argentea_ covers its small dwelling with little bits of vegetable matter, and a nest of _P. rastella_ was placed between two leaves in such a manner as to be entirely hidden. All the species of the genus do not, however, share these habits, _P. mayri_ making a card-nest, like _Dolichoderus_ and some other ants. The species of the genus _Polyrhachis_ are numerous in the tropics of the Old World.

[Illustration: Fig. 64—Nest of _Polyrhachis_ sp. (After Smith.)]

Forbes noticed that a species of this genus, that makes its paper-like nest on the underside of bamboo-leaves produces a noise {156}by striking the leaf with its head in a series of spasmodic taps. The same observer has recorded a still more interesting fact in the case of another species of this genus—a large brown ant—found in Sumatra. The individuals were "spread over a space, perhaps a couple of yards in diameter, on the stem, leaves, and branches of a great tree which had fallen, and not within sight of each other; yet the tapping was set up at the same moment, continued exactly the same space of time, and stopped at the same instant; after the lapse of a few seconds all recommenced at the same instant. The interval was always of about the same duration, though I did not time it; each ant did not, however, beat synchronously with every other in the congeries nearest to me; there were independent tappings, so that a sort of tune was played, each congeries dotting out its own music, yet the beginnings and endings of the musical parties were strictly synchronous."

[Illustration: Fig. 65—_Polyrhachis pandurus_, worker. Singapore.]

Mr. Peal has also recorded that an ant—the name is not mentioned, but it may be presumed to be an Assamese species—makes a concerted noise loud enough to be heard by a human being at twenty or thirty feet distance, the sound being produced by each ant scraping the horny apex of the abdomen three times in rapid succession on the dry, crisp leaves of which the nest is usually composed. These records suggest that these foliage-ants keep up a connection between the members of different nests somewhat after the same fashion as do so many of the terrestrial Camponotides. Although the species of Camponotides have no special organ for the production of sound in the position in which one is found in Myrmicides and Ponerides, yet it is probable that they are able to produce a sound by rubbing together other parts of the abdomen.

{157}SUB-FAM. 2. DOLICHODERIDES.—_Hind body furnished with but one constriction so that only a single scale or node is formed; Sting rudimentary; the poison-sac without cushion._

[Illustration: Fig. 66—_Tapinoma erraticum_, worker. Britain. Upper side and profile.]

The Dolichoderides are similar to Camponotides in appearance, and are distinguished chiefly by the structure of the sting and the poison apparatus. To this we may add that Forel also considers the gizzard to be different in the two sub-families, there being no visible calyx in the Dolichoderides, while this part is largely developed in the Camponotides. This is one of the least extensive of the sub-families of ants, not more than 150 species being yet discovered. Comparatively little is known of the natural history of its members, only a very small number of species of Dolichoderides being found in Europe. The best known of these (and the only British Dolichoderid) is _Tapinoma erraticum_, a little ant of about the size of _Lasius niger_, and somewhat similar in appearance, but very different in its habits. _T. erraticum_ does not cultivate or appreciate Aphides, but is chiefly carnivorous in its tastes. Our knowledge of it is due to Forel, who has noticed that it is very fond of attending the fights between other ants. Here it plays the part of an interested spectator, and watching its opportunity drags off the dead body of one of the combatants in order to use it as food. Although destitute of all power of stinging, this Insect has a very useful means of defence in the anal glands with which it is provided; these secrete a fluid having a strong characteristic odour, and possessing apparently very noxious qualities when applied to other ants. The _Tapinoma_ has no power of ejecting the fluid to a distance, but is very skilful in placing this odorous matter on the body of an opponent by touching the latter with the tip of the abdomen; on this being done its adversary is usually discomfited. This {158}Insect is subterranean in its habits, and is said to change its abode very frequently. _T. erraticum_ occurs somewhat rarely in Britain. Forel has also noted the habits of _Liometopum microcephalum_, another small European species of Dolichoderides. It is a tree-ant, and by preference adopts, and adapts for its use, the burrows made by wood-boring beetles. It forms extremely populous colonies which may extend over several large trees, the inhabitants keeping up intercommunication by means of numerous workers. No less than twelve mighty oaks were found to be thus united into a colony of this ant in one of the Bulgarian forests. The species is very warlike, and compensates for the extreme minuteness of its individuals by the skilful and rapid rushes made by combined numbers on their ant-foes of larger size.

Fritz Müller has given a brief account, under the name of the Imbauba ant, of a Brazilian arboreal ant, that forms small nests in the interior of plants. The species referred to is no doubt an _Azteca_, and either _A. instabilis_, or _A. mulleri_. The nests are founded by fertilised females which may frequently be found in the cells on young _Cecropia_ plants. Each internode, he says, has on the outside, near its upper part, a small pit where the wall is much thinner, and in this the female makes a hole by which she enters. Soon afterwards the hole is completely closed by a luxuriant excrescence from its margins, and it remains thus closed until about a dozen workers have developed from the eggs of the female, when the hole is opened anew from within by the workers. It is said that many of the larvae of these ants are devoured by the grubs of a parasite of the family Chalcididae. This Insect is thought to protect the plant from the attacks of leaf-cutting ants of the genus _Atta_.

We may here briefly remark that much has been written about the benefits conferred on plants by the protection given to them in various ways by ants: but there is reason to suppose that a critical view of the subject will not support the idea of the association being of supreme importance to the trees.[66]

SUB-FAM. 3. MYRMICIDES.—_Pedicel of abdomen formed of two well-marked nodes (knot-like segments). Sting present (absent in the Cryptocerini and Attini). (It should be noted that the {159}workers of the genera Eciton and Aenictus of the subfamily Dorylides have, like the Myrmicides, two nodes in the pedicel.)_

This sub-family consists of about 1000 species, and includes a great variety of forms, but, as they are most of them of small size, they are less known than the Camponotides, and much less attention has been paid to their habits and intelligence. Forel, until recently, adopted four groups: Myrmicini, Attini, Pseudomyrmini and Cryptocerini; but he is now disposed to increase this number to eight.[67] They are distinguished by differences in the clypeus, and in the form of the head; but it must be noted that the characters by which the groups are defined are not in all cases fully applicable to the males. The Cryptocerini are in external structure the most highly modified of Hymenoptera, if not of all the tribes of Insecta.

[Illustration: Fig. 67—_Pheidologeton laboriosus_, large and small workers. East India.]

i. The Myrmicini proper are defined by Forel as having the antennae inserted near the middle, a little behind the front, of the head, which has carinae on the inner sides, but none on the outer sides, of the insertions of the antennae; the clypeus extends between the antennae.

[Illustration: Fig. 68—_Formicoxenus nitidulus_, male. (After Adlerz.)]

Certain genera of small European ants of the group Myrmicini display some most anomalous phenomena. This is especially the case in _Formicoxenus_, _Anergates_ and _Tomognathus_. The facts known have, however, been most of them only recently discovered, and some obscurity still exists as to many of even the more important points in these extraordinary life-histories.

{160}[Illustration: Fig. 69.—_Anergates atratulus_. Europe. A, male, with part of hind leg broken off; B, female, with wings: C, female, after casting the wings and becoming a queen.]

It has long been known that the little _Formicoxenus nitidulus_ lives as a guest in the nests of _Formica rufa_, the wood-ant; and another similar ant, _Stenamma westwoodi_, which shares the same life, was declared by Nylander and Smith to be its male; it was however shown some years ago by André that this is a mistake, and that _S. westwoodi_ is really the male of another ant that had till then been called _Asemorhoptrum lippulum_. This correction left the workers and females of _Formicoxenus nitidulus_ destitute of a male, but Adlerz has recently discovered that the male of this species is wingless and similar to the worker, the female being a winged Insect as usual. It is very curious that the characters by which the male is distinguished from the worker should vary in this species; but according to Adlerz this is the case, individuals intermediate in several points between the males and workers having been discovered. This phenomenon of quite wingless males in species where the female is winged is most exceptional, and is extremely rare in Insects; but it occurs, as we shall see, in one or two other Myrmicides. Charles Darwin made the very reasonable suggestion that winged males may be developed occasionally as an exceptional phenomenon, and it is very probable that this may be the case, though it has not yet been demonstrated. _Formicoxenus nitidulus_ occurs in England in the nests of _Formica rufa_ and of _F. congerens_, but we are not aware that the male has ever been found in this country. The genus _Anergates_ is allied to _Formicoxenus_, and occurs in Central Europe, but has not been found in Britain; the female, as in _Formicoxenus_, is winged and the male wingless, but there is no worker-caste; the male is a rather helpless creature, and incapable of leaving the nest. The species lives in company with _Tetramorium caespitum_ a little ant very like _Myrmica_, and not uncommon in South-East England. The female _Anergates_ is at {161}first an active little creature with wings, but after these are lost the body of the Insect becomes extremely distended as shown in Fig. 69, C; the creature is in this state entirely helpless, and as there are no workers, the _Anergates_ is completely dependent, for the existence of itself and its larvae, on the friendly offices of the _Tetramorium_ that lives with it. The mode of the association of these two Insects is at present both unparalleled and inexplicable, for only workers of the _Tetramorium_ are found in company with the ♂ and ♀ _Anergates_; the community, in fact, consisting of males and females of one species and workers of another. The nests of _Anergates_ are so rare that only a few naturalists have been able to observe them (Schenk, von Hagens, and Forel may be specially mentioned), but in the spots where they occur, nests of the _Tetramorium_, containing all the forms of that species, are numerous, and it therefore seems probable that a young fertile female of the _Anergates_ may leave a nest in which it was born, enter a nest of the _Tetramorium_, and, destroying the queen thereof, substitute herself in the place of the victim; but if this be really the case, the larvae and pupae of the _Tetramorium_ must also be destroyed, for no young of the _Tetramorium_ are ever found in these strange associations. It is very difficult to believe that the _Tetramorium_ workers should be willing to accept as their queen a creature that commenced her acquaintance with them by destroying their own queen or queens and a number of their young sisters; especially as the _Tetramorium_ is a more powerful ant than the _Anergates_, and could readily dispose of the murderous intruder if it were disposed to do so. It is known, however, that colonies of _Tetramorium_ completely destitute of queens sometimes occur, and Wasmann has suggested that the female _Anergates_ may seek out one of these, and installing herself therein as a substitute, may be accepted by the orphaned colony. This plausible hypothesis has still to be verified.

The genus _Cardiocondyla_ also exhibits the phenomenon of apterous, worker-like males, while in one species, _C. emeryi_, a winged male is also known to exist.

_Tomognathus sublaevis_ is a little Myrmicid ant, found rarely in Denmark and Sweden, where its habits have recently been studied by Adlerz. A band of the _Tomognathus_ attack the nest of another little Myrmicid, _Leptothorax acervorum_, and succeed by their own pertinacity and the fears of the _Leptothorax_ in {162}obtaining possession of it; the legitimate owners disappear, leaving the _Tomognathus_ in possession of their larvae and pupae; these complete their development only to find themselves the slaves of _Tomognathus_. The subsequent relations of the two ants are friendly, the slaves even preventing their masters from wandering from the nest when they wish to do so. If an established mixed community of this nature is in want of additional servitors, the _Tomognathus_ secure a supply by raids after the fashion of the Amazon-ant, bringing back to their abode larvae and pupae of _Leptothorax_ to be developed as slaves. It was formerly supposed that the _Tomognathus_ continued its species by perpetual parthenogenesis of the workers, for neither males nor females could be found. Adlerz[68] has, however, now discovered the sexual individuals. The male is an ordinary winged ant, and is so like that sex of the _Leptothorax_, that Adlerz had failed to distinguish the two before he reared them. The females are apterous, and in fact like the workers. It would perhaps be more correct to say that the workers of this species vary greatly but never become winged; some of them have ocelli and a structure of the thorax more or less similar to that of winged females, though none have been found with wings. Certain of these females possess a receptaculum seminis, and Adlerz treats this as the true distinction between female and worker. In accordance with this view the female of _Tomognathus_ may be described as a worker-like individual possessing a receptaculum seminis, and having more or less of the external structures of winged females, though never being actually winged. It is probable that other workers reproduce parthenogenetically. The males of this species will not unite with females from the same nest, thus differing from many other ants, in which union between individuals of the same nest is the rule. Finally, to complete this curious history, we should remark that the larvae of the _Tomognathus_ are so similar to those of the _Leptothorax_ that Adlerz is quite unable to distinguish the two.

_Strongylognathus testaceus_ and _S. huberi_ live in association with _Tetramorium caespitum_, and are cared for by these latter ants; it is notable that as in the case of the slave-making _Polyergus rufescens_ the mandibles of the _Strongylognathus_ are cylindrical and pointed, and therefore unsuitable for industrial occupations. {163}_S. testaceus_ is a weak little ant, and lives in small numbers in the nests with _T. caespitum_, which it is said to greatly resemble in appearance. The proportions of the forms of the two species usually associated is peculiar, there being a great many workers of _T. caespitum_ both in the perfect and pupal states, and also all the sexes of the _Strongylognathus_, of which, however, only a few are workers. This would seem to suggest that _S. testaceus_ attacks and pillages the nests of _T. caespitum_ in order to carry off worker pupae, just as _Polyergus rufescens_ does. But the facts that _S. testaceus_ is a weaker Insect than the _Tetramorium_, and that only a few of its worker-caste are present in a community where there are many workers of the _Tetramorium_, seem to negative the view that the latter were captured by the former; and the mode in which the associated communities of these two species are started and kept up is still therefore in need of explanation.

_Strongylognathus huberi_ is a much stronger Insect than its congener, _S. testaceus_, and Forel has witnessed its attack on _Tetramorium caespitum_. Here the raid is made in a similar manner to that of _Polyergus rufescens_ on _Formica_; the _Tetramorium_ is attacked, and its pupae carried off to the abode of the _Strongylognathus_ to serve in due time as its slaves. The mandibles of _S. huberi_, being similar in form to those of _Polyergus rufescens_ are used in a similar manner.

Although _T. caespitum_ is common enough in South-East England, it is to be regretted that none of the guests or associates we have mentioned in connection with it occur in this country. It is a most variable species, and is distributed over a large part of the globe.

Our British species of Myrmicides, about ten in number, all belong to the group Myrmicini; none of them are generally common except _Myrmica rubra_, which is a most abundant Insect, and forms numerous races that have been considered by some entomologists to be distinct species; the two most abundant of these races are _M. ruginodis_ and _M. scabrinodis_, which sometimes, at the time of the appearance of the winged individuals, form vast swarms.

The tiny _Monomorium pharaonis_ is a species that has been introduced into Britain, but now occurs in houses in certain towns; it sometimes accumulates on provisions in such numbers as to be a serious nuisance. Seventeen thousand {164}individuals weigh 1 gramme, and it is probable that a nest may include millions of specimens.

The genus _Aphaenogaster_[69] and its immediate allies include the harvesting ants of Europe and North America: they form subterranean nests consisting of isolated chambers connected by galleries; some of the chambers are used as store-houses or granaries, considerable quantities of corn, grass, and other seeds being placed in them. _A. structor_ and _A. barbarus_ have been observed to do this in Southern Europe, by Lespès, Moggridge, and others.

[Illustration: Fig. 70—_Aphaenogaster (Messor) barbarus._ Algeria. A, male; B, winged female; C, large worker or soldier; D, small worker. × 3/2.]

In the deserts about Algeria and Tunis a harvesting ant, _Aphaenogaster (Messor) arenarius_, is an important creature: its subterranean dwellings are very extensive, and are placed at a depth of several feet from the surface. Entrance to these dwellings is obtained by small holes, which are the orifices of galleries many feet in length: the holes are surrounded by pellets of sand projecting somewhat above the general surface, and consequently making the places conspicuous. The subterranean works occupy an area of fifty or a hundred square yards excavated at a depth of three to six feet. In these immense nests there exists a form of worker, of very small size, that never comes to the surface.[70]

_Pogonomyrmex barbatus_ and other species have been observed to do harvesting in North America. After the workers of _P. barbatus_ have taken the seeds into the nest they separate the husks and carry them out, depositing them on a heap or {165}kitchen-midden, formed near by. M‘Cook has witnessed and described the process of stripping the seeds.

Certain genera—e.g. _Aphaenogaster_, _Pheidole_—exhibit great disparity in the forms of the workers, some of which are of size much superior to the others, and possess disproportionately large heads; these large individuals are found in the same nest as the smaller forms. All the intermediate forms may frequently be found, and at the same time, in the genus _Aphaenogaster_; but in _Pheidole_ intermediates are of the utmost rarity.

The genus _Cremastogaster_ is remarkable on account of the shape of the hind body and its articulation, which give the abdomen the appearance of being put on upside down. This mode of articulation may allow the Insect to threaten its enemies when they are in front of it; but it is doubtful whether the _Cremastogaster_ possesses an effective sting.

[Illustration: Fig. 71—_Cremastogaster tricolor_, worker. A, with abdomen extended; B, uplifted.]

ii. The group Attini is distinguished by the presence of a carina near the eye, by the antennae being inserted at a moderate distance from one another, by the clypeus being prolonged backwards between them; and by the absence of a sting. The group is not represented in Europe, but in Tropical America the ants belonging to it are amongst the most important of natural objects. The species of the genus _Atta_ (usually styled _Oecodoma_) are the formidable leaf-cutting ants of America. They occur in enormous colonies in certain places, and will in a short time completely strip a tree of its leaves. As they appear to prefer trees of a useful kind, especially those planted by man, their ravages are often of the most serious nature. The natives, feeling it hopeless to contend with these Insect hordes, only too frequently abandon all attempts to cultivate the trees and vegetables the Insects are fond of. Both Bates and Belt have {166}given accounts of some points in the economy of these ants. They are amongst the largest of the Formicidae, the females in some cases measuring about two and a half inches across their expanded wings; the males are much smaller, but are less dissimilar to their partners than is usual among ants. The workers, on the other hand, are so extremely different, that no one would suppose them to be at all related to the males and females (see vol. v. Fig. 339).

The mode of operation of these ants is to form paths from their formicary extending for a considerable distance in various directions, so that they have a ready access to any spot in a district of considerable extent; when a tree or bush is found bearing leaves suitable for their purposes, the worker ants ascend it in large numbers and cut up the leaves by biting out of them pieces similar in size and shape to a small coin; these pieces are then carried back in the jaws of the ants to their nests; the ant-paths are therefore constantly traversed by bands of little creatures carrying burdens homewards, or hurrying outwards in search of suitable trees.

The formicaries are of considerable size, and are described as consisting of low mounds of bare earth of considerable extent. Bates speaks of as great a circumference as forty yards; these accumulations of earth have frequently an appearance different from the adjoining soil, owing to their being formed of subsoil brought up from below; they are kept bare by the ants constantly bringing to and depositing on the surface fresh material resulting from their subterranean excavations. The true abodes, beneath the earth, are of greater extent than the mounds themselves, and extend to a considerable depth; they consist of chambers connected by galleries.

The leaf-cutting ants extend their range to North America, and M‘Cook has recently called attention to a case there in which _A. fervens_ made an underground route at an average depth of 18 inches, and at an occasional depth of 6 feet, extending 448 feet entirely beneath the earth, after which it was continued for 185 feet to reach a tree which the ants were engaged in defoliating. This route, extending altogether to a length of more than 600 feet, presented only a very slight deviation from a straight line drawn between the point of departure and the object to be attained. By what sense this ant was enabled {167}to make a subterranean tunnel in a straight line to a desired object situated at so great a distance, we know not.

The use the leaf-cutting ants make of the enormous amount of material they gather was for long a subject of debate, and has only recently been ascertained by the observations of Möller. After being carried to the nest the pieces of leaves are cut into small fragments by another set of workers and formed into balls, which are packed in various parts of the nest, and amongst which the mycelium of a fungus—_Rozites gongylophora_—ramifies. This fungus the ants cultivate in the most skilful manner: they manage to keep it clear from mouldiness and bacterial agents, and to make it produce a modified form of growth in the shape of little white masses, each one formed by an agglomeration of swellings of the mycelium. These form the chief food of the colony. Möller ascertained by experiment that the results were due to a true cultivation on the part of the ants: when they were taken away from the nests, the mycelium produced two kinds of conidia instead of the ant-food.

Many details of the economy of these leaf-cutting ants are still very imperfectly known. The large-headed forms, called soldiers, have been the subject of contradictory statements; Bates having concluded from his own observations that they are harmless, while Mr. J. H. Hart assures us that they are very fierce and vindictive, and inflict very serious wounds by biting (the Attini do not sting). We anticipate that the observations of both these naturalists will prove to be substantially correct, and that the differences in habits will be found to be owing to distinctions in the conditions of the community. In connection with this point we may remark that the function of the excessively large heads of certain kinds of soldier-ants is still obscure. In the East Indian _Pheidologeton diversus_ the big soldiers are quite one hundred times as large as the smaller workers. As these latter bite viciously it would naturally be supposed that their gigantic _confrères_ with enormous heads would be warriors of a most formidable nature; but, as a matter of fact, the giants are unable to bite even when they try to do so. Aitken has somewhere suggested that these enormous individuals play the part of state elephants; and we have been informed by Colonel Bingham that the small ants may frequently be seen riding in numbers on their unwieldy fellows. We anticipate {168}however, that some other function will be found to exist for these forms with enormous heads. An examination of their organs of sense and of voice is very desirable.

Details of the modes in which the great communities of the leaf-cutting Attidae are maintained, are still wanting. The females do not, we have been informed by Mr. Hart, possess any considerable powers of aftergrowth, so that there is no reason to suppose them to be unusually prolific. At certain seasons great swarms of winged individuals are produced, and after leaving the nests pair in the manner of our European _Myrmica_. Possibly the females may, after losing their wings, again enter the large communities. Von Ihering states that the workers of _Atta lundi_ are fertile.

iii. The group Pseudomyrmini includes the genera _Pseudomyrma_ and _Sima_, which are by some entomologists treated as but a single genus. The antennae are inserted near together on the front of the head; there is no carina on the head external to their insertion, and the clypeus does not extend forwards between them. The Insects are usually of elongate form, possess a sting, and have a naked pupa. The group occurs in both hemispheres, but is exclusively exotic, and but little is known of the habits of its members. Forel has recently observed that numerous species live inside dried stems of grass or in hollow twigs, and are beautifully adapted for this mode of life by their elongate form, some of them being as slender as needles. Some interesting observations have been made in Nicaragua by Belt on _Pseudomyrma bicolor_ and its relations with an acacia-tree, in the thorns of which it lives. The acacia in question is called the bull's-horn thorn, because the branches and trunk are armed with strong curved spines, set in pairs, and much resembling the horns of the quadruped whose name they bear. The ant takes possession of a thorn by boring a small hole near the distal extremity, and forms its nest inside. The leaves of this plant are provided with glands that secrete a honey-like fluid, which it appears forms the chief, if not the sole, subsistence of the ant. Belt considers that the presence of the ant is beneficial to the acacia; he supposes that the ants assume the rights of proprietors, and will not allow caterpillars or leaf-cutting ants to meddle with their property; the leaves are, he thinks, so preserved to the benefit of the tree.

{169}[Illustration: Fig. 72—_Sima rufo-nigra_ and its associates. A, winged female; B, worker, of the ant; C, _Rhinopsis ruficornis_; a fossorial wasp of the sub-family _Ampulicides_; D, a spider, _Salticus_ sp. The coloration is extremely similar in all these creatures.]

Rothney has given some particulars of the habits of _Sima rufo-nigra_, an ant of this group that appears to be not uncommon near Calcutta, where it lives on the trunks of trees in company with a spider and a wasp that greatly resemble it in form and in colour. The three creatures seem to associate together on amicable terms; indeed the wasp and the ant occasionally indulge in wrestling matches without doing one another any serious harm. In connection with this fact we may observe that other species of ants have been observed to indulge in sports and feats of agility.

_S. leviceps_, an Australian species of this genus, is furnished with a stridulating file that has the appearance of being constructed so as to produce two very different kinds of sounds.

[Illustration: Fig. 73—Stridulating file of _Sima leviceps_.]

iv. The Cryptocerini are distinguished from other ants by their antennae being inserted at the sides of the head, where they are placed between ridges or in a groove into which they can be withdrawn; when in some cases they are entirely concealed. These ants assume a great variety of shapes and forms, some of which look almost as if they were the results of an extravagant imagination. The skeleton is usually much harder than it is in other {170}ants; the abdomen consists almost entirely of one very large segment, there being, however, three others visible at its extremity; these segments can be only slightly protruded, and the ants have no power of stinging. They are probably most of them arboreal in their habits. Nearly all of the known forms are exotic. According to the observations of Bates the species of the genus _Cryptocerus_ in the Amazons Valley may frequently be observed in dry open places on low trees and bushes, or running on branches of newly felled trees; they also visit flowers abundantly. The species generally are wood-borers, usually perforating the dead branches of trees. _C. atratus_ has been observed to construct its nests in the dead, suspended branches of woody climbers; a number of neatly drilled holes are all that can be seen externally; but, inside, the wood is freely perforated with intercommunicating galleries. Each community appears to consist of a single female and two kinds of workers; the latter in some species are quite unlike each other, differing in the form of the head, and in the armature of the thorax and nodes of the peduncle. The species of _Cryptocerus_ appear to be omnivorous, and are frequently attracted by the excrement of birds. The pupae are not enclosed in a cocoon. In the South of Europe two very minute ants, of the genera _Strumigenys_ and _Epitritus_, belonging to this family, are met with under very large stones partly embedded in the earth. They are of the greatest rarity.

[Illustration: Fig. 74—_Cyrptocerus atratus_, worker. Amazons. The compressed first joint of the hind foot is shown at _a_ and _b_ in different positions.]

SUB-FAM. 4. PONERIDES.—_Hind body elongate, furnished with one node at the base, and having also great capacity of movement between the first and second segments, between which there is usually a slight constriction. Sting well developed._

This sub-family includes numerous genera and about 400 species. The Ponerides have an elongate hind-body; the second segment behind the node is capable of great movement in and out of the preceding segment, and for this purpose is furnished with a basal portion slightly more slender than the apical part; this {171}basal part is usually concealed within the more anterior segment, the hind margin of which embraces it very closely. On the middle of the dorsal aspect of this articulation there is usually placed a stridulating organ, consisting of an elongate band or patch of very fine lines; this gives out a sound when the second segment is moved in and out of the first at a time when the posterior edge of the latter is slightly depressed.

We follow Forel in including the Australian bull-dog ants—_Myrmecia_—in Ponerides, as well as the Odontomachi. The former have, however, a definite pedicel, consisting of two nodes (Fig. 76). In the Odontomachi the mandibles are approximate at their bases, being inserted on the middle of the front of the head (Fig. 77).

This sub-family includes a considerable number of species, and is found in all parts of the world. Extremely little is known as to the habits, but the true Ponerides do not, so far as is known, occur in large communities, and it seems probable that they are destitute of the powers of combined action that are so remarkable in the Camponotides, and in some of the Myrmicides and Dorylides. Most of the species that have been described are known by only one sex, so that very little knowledge exists as to the sexual distinctions; but from the little that is known it would appear that the three sexual forms are not so differentiated as they are in most of the Camponotides and Myrmicides.

[Illustration: Fig. 75—_Dinoponera grandis_, worker. Amazons.]

The species of the genus _Leptogenys_ are believed by Emery and Forel to possess an apterous female. Mr. Perkins has observed that the Hawaiian _L. falcigera_ has workers with different kinds of sting, but no true female. Males of this species are, however, abundant. Wroughton has recently discovered that one member of this genus is of Termitophagous habits, but this is not the case with _L. falcigera_. _Dinoponera grandis_ (Fig. 75) is the largest of the Ponerides, its {172}workers attaining an inch and a quarter in length. This Insect, according to Bates, marches in single file in the thickets at Pará; its colonies consist of a small number of individuals, and are established at the roots of slender trees. The effects of its powerful sting are not so serious as is the case with some of the smaller ants.

In Britain we have only two representatives of the sub-family, viz. _Ponera contracta_, a small ant of dirty-yellow colour, found rarely in the Southern counties, living in moss or under stones. Its colonies consist of only a few individuals; Forel giving fifty as the highest number he has observed. The second species, _P. punctatissima_, presents the almost unique peculiarity of possessing two forms of the male sex, one of them resembling the worker in most of its peculiarities, and in being destitute of wings, while the other is winged, as is usual in male ants. In the island of St. Vincent another species of _Ponera_ has been discovered having an apterous and worker-like male, and was named by Forel _P. ergatandria_.[71] The discovery of this form has led him to express some doubt as to whether _Ponera punctatissima_ has two forms of males; but it seems probable that it really is so, the ergatoid males being produced under somewhat different circumstances from the normal males. We shall subsequently see that _Cardiocondyla_ and a few other Myrmicides exhibit an analogous peculiarity.

The genus _Myrmecia_ is confined to the Australian continent and Tasmania, and includes a considerable number of species of large and moderate-sized ants, the classification of which has been a subject of difference of opinion. This has arisen from the fact that the nodes of the abdominal pedicel are more similar to those existing in the Myrmicides than to those of the typical Ponerides. There are, however, some American members of the latter sub-family (_Paraponera clavata_, _e.g._) that differ but little in this point from _Myrmecia_, and, moreover, the pupae of _Myrmecia_ are enclosed in a cocoon, while in the Myrmicides they are usually naked. On the other hand the nests are, it appears, very large and populous, more like what exists in the Myrmicides; there is no true stridulating organ on the first abdominal segment. The genus is therefore one of those interesting anomalies that form so large a proportion of the Australian {173}fauna, and will probably be ultimately treated as a distinct sub-family. There are about thirty species.

The ants of this genus are well known to the residents in Australia, where they are called "bull-dog ants." They form large mounds of earth for their nests. The workers, and females (Fig. 76) are much alike except during the period when the latter are still carrying their wings. The males, however, differ considerably, being of more slender form, and possessing only insignificant mandibles, and straight antennae with a quite short basal joint.

[Illustration: Fig. 76—_Myrmecia pyriformis._ Australia. Female after casting wings.]

Forel considers _Myrmecia_ to be the most formidable of all the ants; the hills are said to be sometimes five feet high, and the colonies are immense in numbers, while the Insect is an inch or more in length, and armed with a very powerful sting, the use of which on the human body is said to give rise in some cases to serious symptoms. On the other hand, we have seen statements to the effect that the sting of _Myrmecia_ has only very evanescent sequelae; it is also said that the ant-hills have only a slight elevation, so that probably both these points differ according to the species. It appears from a communication of Miss Shepherd's that the formidable _Myrmecia forficata_ has its larvae destroyed by a parasitic Hymenopteron (_Eucharis myrmeciae_) of brilliant colour and considerable size, so that we have the curious fact of the hordes of this most formidably armed ant, which possesses also large eyes, falling a victim to a brilliant and very conspicuous Insect. Particulars of this case of parasitic attack are still wanting. There are other cases known of the larvae of ants being destroyed by parasitic Diptera and Hymenoptera, but in none of them have any sufficient observations been made as to the mode in which the attack is made. Lowne says that _M. gulosa_ itself attacks large beetles of the genus _Anoplognathus_ and buries them; and he also adds the very curious statement that _M. nigrocincta_, when running, is able to take leaps of a foot in length.

The Odontomachi were formerly considered a distinct sub-family, distinguished by the peculiar mandibles (Fig. 77). {174}Many of the Ponerides have elongate mandibles, but they are inserted at the sides of the front of the head, not in the middle of the front. These organs in some species of Odontomachi serve as levers, by aid of which the Insect can execute considerable leaps. In only a few species are the males known; Mayr and Forel state that they are destitute of the peculiar mandibles characteristic of the worker.

[Illustration: Fig. 77—_Anochetus ghiliani_, worker. Tangier.]

The unique European representative of the Odontomachi, _Anochetus ghiliani_, occurs in Andalusia. Near Tangier Mr. George Lewis found it to be not uncommon; but the sexes are not known, and it even appears doubtful whether there exists any well-marked division between workers and female. Lewis observed, among the ordinary forms, individuals with longer bodies, usually one in a nest, and he supposed these to be females; Saunders, on examining these examples, found them to possess distinct ocelli, and therefore agreed with Lewis as to their being the female sex. Dr. Emery subsequently examined these same specimens, and took what is scarcely a different view, viz. that they are not females but an intermediate form; and he also expressed the opinion that "the true female may not exist." The male of _Anochetus_ is not known. The female of _A. mayri_, a Neotropical species, has rudimentary wings.

SUB-FAM. 5. DORYLIDES.—_Clypeus extremely small, the antennae inserted very near the front margin of the head. Hind body usually elongate and subcylindrical, with an imperfect pedicel formed by the constriction of the back of the first segment, but occasionally there are two nodes in the workers. Distinctions between the two sexes, and between the workers and sexed forms, enormous, the queens truly wingless. The females and workers usually blind, or at any rate destitute of facetted eyes. (In Ecitonini the antennae are not inserted quite at the front of the head, and there are two nodes in the pedicel.)_

{175}We have reserved to the end of the ants the consideration of the two groups Dorylides and Amblyoponides, recent investigations having rendered it somewhat doubtful whether they can be maintained as distinct from Ponerides. The chief character of the Dorylides is that the males are much less ant-like in form than they are in the other groups, and that the distinction between the females and workers are enormous. The little that is known as to the males and females of this group suggests the view that these sexes may offer sufficient reason for keeping the Dorylides as a group distinct from the other ants; but it must be admitted that it is very difficult to find satisfactory characters to distinguish the workers of the Dorylides in some cases from the Ponerides, in others (_Eciton_) from the Myrmicides.[72]

[Illustration: Fig. 78—Various forms of worker of _Eciton hamatum_. Guatemala.]

The Dorylides are of great interest, for they exhibit the remarkable phenomenon of a nomadic social life, accompanied by imperfect sight in the wanderers. The sub-family includes two apparently distinct groups: (1) the Ecitonini, peculiar to the New World, and having a close relationship with the Myrmicides; and (2) the Dorylini existing chiefly in the eastern hemisphere, and related closely by its workers to the Ponerides and Amblyoponides. (i.) The Ecitonini consist of the species of the genus _Eciton_, the wandering ants of America, and of _Labidus_, which there is now good reason for believing to consist of the males of _Eciton_. The female is still uncertain. The _Eciton_ are nomad ants having no fixed abode, but wandering from place to place in search of prey, and forming temporary resting-places. The {176}species are rather numerous, and the habits of several have been described by Bates, who, however, was not acquainted with some of the most peculiar features in their biology, these having been since revealed by Belt and W. Müller.

These ants are predaceous in their habits, and some of the species travel in vast hordes; they occasionally enter houses and clear them of much of the vermin with which they may be infested. They have no facetted eyes, some of the forms being quite blind, while others have a pair of peculiar lenses in the position normally occupied by the compound eyes. Usually there are two castes of the workers, and in some species these are very different from one another, the mandibles being in the larger form very elongate, cylindrical and unfit for industrial purposes, while the individuals of the smaller caste have the outer jaws shorter, with their edges apposed and coadapted: in other species individuals with mandibles differentiated from the normal form do not exist. The nomad habits of these ants were described by Bates, but the detection of their temporary resting-places was reserved for Belt, who found that, after their plundering raids, they retired to a place of concealment, and there clustered together in a compact mass like a swarm of bees. Belt says: "They make their temporary habitations in hollow trees and sometimes underneath large fallen trunks that offer suitable hollows. A nest that I came across in the latter situation was open at one side. The ants were clustered together in a dense mass, like a great swarm of bees, hanging from the roof, but reaching to the ground below. Their innumerable long legs looked like brown threads binding together the mass, which must have been at least a cubic yard in bulk, and contained hundreds of thousands of individuals, although many columns were outside, some bringing in the pupae of ants, others the legs and dissected bodies of various Insects. I was surprised to see in this living nest tubular passages leading down to the centre of the mass, kept open, just as if it had been formed of inorganic materials. Down these holes the ants who were bringing in booty passed with their prey. I thrust a long stick down to the centre of the cluster and brought out clinging to it many ants holding larvae and pupae."

Turning now to the _Labidus_ question: many American species of this genus have long been known, though all of them {177}by the male sex only. The discoveries (to be subsequently alluded to) made in the Old World as to the relations between the driver ants and _Dorylus_ raised a suspicion that _Labidus_ might be the male of _Eciton_, the distinctions in the two cases being very analogous: this conjecture has been almost proved to be correct by the recent observations of Hetschko and W. Müller. The latter, who observed the temporary nests of _Eciton hamatum_, confirms Belt's statements as to the ants hanging together in clumps, like swarms of bees; he also states that the change from one temporary abode to another takes place at night, though, as is well known, the hunting forays of this ant are carried on in the daytime. The periods of migration appear to be determined by the time at which all the larvae have assumed the pupal state, this at any rate being the time chosen in the case observed by Müller. This naturalist bagged a part of one of the nests by the aid of ether, and found the larger portion to consist of pupae; there were also some larvae and eggs; a specimen of _Labidus_ (_L. burchelli_) was also found on friendly terms with the _Eciton_-workers; and myrmecophilous Coleoptera were discovered. The pupae are enclosed in cocoons. Persistent search failed to reveal any female, but the examination was made under great difficulties. Müller also states that the earliest pupated larvae yield soldiers, the latest the smallest forms of workers. From observations made by Forel on a pupa, it seems probable that a wingless form of male may be found to exist. If therefore, as appears practically certain, _Labidus_ is the winged male of _Eciton_, it is probable also that males of more or less worker-like form exist, as is now known to be the case in some other Formicidae.

We may here notice a peculiar apterous female ant recently described by André under the name of _Pseudodicthadia incerta_. He thought this might prove to be the female of _Eciton-Labidus_; but his description and figure are imperfect, and do not greatly support his idea of a connection between _Eciton_ and _Pseudodicthadia_.

ii. The group Dorylini includes the genus _Dorylus_, which was founded many years ago for Insects very like _Labidus_. As in the case of the American Insect named, males only were known; two or three allied genera, consisting exclusively of individuals of the sex mentioned, were subsequently described. In the {178}regions inhabited by these males numerous species of blind ants are known, but only in the worker form, and were, or still are, referred to genera called _Typhlopone_ and _Anomma_. Nothing that could be considered to be a female pertaining to any of these Insects was discovered until Gerstaecker described under the generic name _Dicthadia_ an extraordinary apterous female ant found in Java, and it was suspected that it might be the long-expected female of the male _Dorylus_ and of the worker _Typhlopone_ or _Anomma_. This remained for many years without confirmation, but in 1880 Trimen announced the discovery in South Africa of an enormous apterous female ant, allied to _Dicthadia_; it had been disinterred from a nest of small red ants believed (wrongly) to be _Anomma_. As _Dorylus_ had been previously found in connection with allied worker ants it has since then been clear that notwithstanding the enormous differences existing between these three forms they may all pertain to one (or to closely allied) species. From this summary the student should understand that he will find in myrmecological literature many references to two or three genera that really belong to one species.

[Illustration: Fig. 79—_Dorylus helvolus._ Africa. A, male; B, female (_Dicthadia_); C, worker major (_Typhlopone_); D, worker minor. (After Emery.)]

The workers of the Dorylini at present known are without exception quite blind, and are believed to be all of predaceous habits; it is thought by some that they have no fixed abodes, but, like the Ecitonini, frequently change their residence, and it has been suggested that in doing so they make use of the nests of other ants as temporary abodes; all these points are, however, still unsettled, and as there are several genera it is not unlikely that considerable variety will be found to prevail. The driver ants of Africa, belonging to the genus _Anomma_, are in some {179}respects similar to _Eciton_ in habits, as they enter human habitations and cause nearly everything else to quit; it is probable that they are also exclusively carnivorous. Savage detected the nests of _A. arcens_, but the account he has given of them is too vague to permit one to decide whether the assemblages he saw were of a nomad kind. The workers of this species vary greatly in size, and Emery has recently stated that he believes all the supposed species of the genus to be merely varieties of _A. burmeisteri_. The female of the driver ants is still quite unknown. A _Dorylus_ has been ascertained to be the male of _Typhlopone_. The male _Dorylus_ (Figs. 79, A, and 80) is of great interest, for the propodeum is in a more primitive form than it is in any other petiolate Hymenopteron known to us, while at the same time the pronotum and mesonotum are very highly developed. The genus _Typhlatta_ Sm. has been recently identified by Wroughton and Forel as the worker-condition of which _Aenictus_ is the winged male. The genus _Alaopone_ will probably be found to have some species of _Dorylus_ as its male.

[Illustration: Fig. 80—Body of male of _Dorylus_ sp. Delagoa Bay. _a_, pronotum; _b_, _c_, divisions of mesonotum; _d_, metanotum; _e_, propodeum; _f_, first abdominal segment; _g_, _h_, points of insertion of anterior and posterior wings.]

The females of the Dorylides are amongst the rarest of Insects, and are also amongst the greatest of natural curiosities. Although worker ants and female ants are merely forms of one sex—the female—yet in this sub-family of ants they have become so totally different from one another in size, form, structure, and habits that it is difficult to persuade oneself they can possibly issue from similar eggs. In the Insect world there are but few cases in which males differ from females so greatly as the workers of Dorylides do from the females, the phenomena finding their only parallel in the soldiers and females of Termites; the mode in which this difference is introduced into the life of the individuals of one sex is unknown. The largest of all the Dorylides are the African Insects of the genus _Rhogmus_. Only the male is known.

{180}The specimens of female Dorylides that have been detected may, after fifty or sixty years of research, be still counted on the fingers. As the greatest confusion exists in entomological literature owing to the forms of a single species having been described as two or three genera, the following summary of the principal names of genera of Dorylides may be useful:—

_Eciton_ = the workers, _Labidus_ = male: ♀ unknown.

_Pseudodicthadia_: female only known, possibly that of _Eciton_.

_Cheliomyrmex_: workers and soldiers only known.

_Aenictus_ = the male, _Typhlatta_ = worker: ♀ unknown.

_Rhogmus_: male; female unknown. (According to Emery the worker is very small and like _Alaopone_.)

_Anomma_: only worker known; male probably a _Dorylus_.

_Dorylus_ = male; _Dicthadia_ = ♀: _Alaopone_ and _Typhlopone_ = workers.

SUB-FAM. 6. AMBLYOPONIDES.—_Abdomen destitute of distinct pedicel; the articulation between the first and second segments behind the true petiole being broad._

[Illustration: Fig. 81—_Amblyopone_, worker. Tasmania.]

We follow Forel in separating _Amblyopone_ and a few allies from the Ponerides, because the abdominal pedicel is more imperfect than in any other ants. It is, indeed, very difficult to frame a definition that will include the Amblyoponides among ants, and at the same time separate Formicidae and Scoliidae. Forel considers the Amblyoponides to approach closely to certain divisions of the Scoliidae (Thynnides, _e.g._). Little is known of these Insects, though they are widely distributed. _Amblyopone_ is found in Australia and New Zealand; the allied genus _Stigmatomma_ has a wide distribution, occurring even in Europe. The social life is believed to be imperfect, and the habits subterranean and sedentary. The males and females are winged; the latter much resemble the workers, which are nearly blind, and have a considerable general resemblance to _Anomma_ in Dorylides.

ASSOCIATION OF ANTS WITH OTHER KINDS OF INSECTS.—We have already alluded to the fact that a few species of ants are {181}used by other species as attendants, and that the two kinds then live together quite amicably; and we have also seen that a few ants live in association with other species on terms that are not yet understood. One little ant, _Formicoxenus nitidulus_, lives only in the large nests of _Formica rufa_; these ants tolerate the little _Formicoxenus_, which so far as is known does them neither good nor harm. There are also a considerable number of species of small ants that are in the habit of choosing the neighbourhood of larger species for their dwelling-places; in some cases the nests are constructed actually within a portion of the edifice of the more powerful species, and the rule then appears to be that these neighbours do not molest one another. Notwithstanding the militant lives that many of them lead, ants cannot be considered as of generally ferocious disposition.

But the most remarkable point in connection with their toleration consists in the fact that the nests of many species are inhabited by quite a colony of foreign Insects of various Orders; many of these, being found nowhere else, are spoken of as ants'-nest or Myrmecophilous Insects.[73] The relations of ants with other Insects are of the most varied and complex character; some of their guests live with them on terms of the most intimate association, being indeed absolutely dependent for their existence on the good offices of their hosts; others of the ants'-nest Insects are enemies, while others are neutral or indifferent to the ants. We have already mentioned that the guests migrate in company with their hosts.

Many species of ants derive a considerable portion of their sustenance from the sweet substances excreted by Aphidae. Ants may constantly be seen occupied with clusters of Aphidae, and it is said that the ingenious little creatures defend from enemies the manufacturers of the sweet-stuff they are so fond of, even going so far as to form barricades and covered places for the isolation and protection of this peculiar kind of cattle; a few ants keep some of the root-feeding Aphidae in their nests. Coccidae and other Homoptera, which also excrete much matter of a sugary nature, are likewise consorted with by ants; as are also the larvae of some butterflies of the family Lycaenidae; these latter being believed to furnish to the ants some substance of a nutritious kind.

{182}[Illustration: Fig. 82—The beetle, _Atemeles_, soliciting food from an ant. (After Wasmann.)]

The Insects we have spoken of are, however, rather of the nature of ant-cattle, and the fondness of the ants for them is not very remarkable. The relations of the ants to the peculiar species of Insects that live only in or around their nests are much more extraordinary. The greater number of these guests belong to the Order Coleoptera, and of these there are many hundreds—probably many thousands—of species that depend on ants for their existence. The family Pselaphidae furnishes a large number of ants'-nest beetles, and it appears probable that most of them excrete some sugary substance of which the ants are fond. Many of these Pselaphidae are of the most fantastic shapes, more especially the members of the sub-family Clavigerides. But the most curious of all the ant's-nest beetles are the Paussidae, a family exclusively dependent on ants, and having the curious faculty, when disturbed, of bombarding—that is, of discharging a small quantity of vapour or liquid in a state of minute subdivision accompanied by a detonation. Many species of _Staphylinidae_ are peculiar to ant's-nests, and most of them are indifferent or inimical to their hosts, but some of them, such as _Atemeles_ (Fig. 82) and _Lomechusa_, are doubtless producers of sweet stuff that is liked by the ants. The ants feed some of their special favourites amongst these guests in the same manner as they feed one another, viz. by opening the mouth, causing a drop of liquid to appear on the lip, and remaining passive while the guest partakes of the proffered _bonne bouche_. This way of giving food to other individuals is a most remarkable feature in the character of ants; it is not the same system that they adopt in feeding the larvae, for they then make a series of actual movements, and force the nutriment into the mouths of the grubs. Besides the Insects we have mentioned there are also Orthoptera, Hemiptera, Poduridae and Thysanura, Acari, and small Isopod crustaceans that live exclusively in company with ants. We have mentioned that a few Hymenopterous and Dipterous parasites have been detected living at the expense of ants; it is probable that closer observation of the ant larvae and pupae in their nests {183}will disclose a greater number of the parasites of this latter class.

Much attention has been given to the relations between ants and their guests by Wasmann.[74] He arranges them in four categories; 1, "Symphily" for the true guests, which are fed and tended by the ants, the guests often affording some substance the ants delight in; 2, "Metochy," the class of tolerated guests, being so far as is known not disagreeable to the hosts; 3, "Synecthry," including those Insects, etc., to which the ants are hostile, but which nevertheless maintain themselves in the midst of their foes; 4, Parasites, dwelling in the bodies of the adult, or of the young ants. Many of these ants'-nest Insects present a more or less perfect resemblance to the ants in one or more points, such as sculpture, colour, size, or form. To these resemblances Wasmann attaches great importance. We should, too, notice that some of the inquilines[75] have become acquainted with the movements and habits of the ants, and stroke them (as the ants do one another) to induce them to disgorge food in the manner we have alluded to. According to Janet, ants of the genus _Lasius_ are infested by Acari of the genus _Antennophorus_. The ants carry the mites, which assume positions so as not to cause greater inconvenience than is inevitable. Moreover, the ants give food to the mites when requested, and behave in a most obliging way to them, though there is not any reason for supposing that in this case the ants derive any benefit from the Symphily.

The relations between ants and plants have been of late years much discussed. We have already briefly alluded to the subject when speaking of the Pseudomyrmini. We will here only remark that ants frequent plants not only for the purpose of securing the sweet stuff excreted by the Aphidae that live on them, but also for the sake of getting the sweet products the plants themselves afford. Mr. Aitken, speaking of ants in India, says: "I have come to the conclusion that one of the most important sources of food-supply which ants have is the sacchariferous glands to be found at the bases of so many leaves." It is supposed that the ants are on the whole beneficial to the plants that thus afford them supply; and this fact is considered by many to afford an adequate explanation of the existence of these interesting relations.

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