Part 7

The larvæ and pupæ of the different kinds of insects which undergo a complete metamorphosis have not the same shape of body. Among the larvæ may be distinguished _caterpillars_, _grubs_, and _maggots_. The _caterpillars_ (Fig. 60) have a clearly marked head with hard covering, three pairs of jointed thoracic legs, and a varying number of unjointed pro-legs. They are usually variegated or green in colour, and are divided into _true caterpillars_ and _false caterpillars_ (Figs. 60, 63, and 64). The first, after the resting pupa stage, become butterflies or moths; the latter saw-flies. The true caterpillars have two to five pairs of pro-legs, the false caterpillars six to eight pairs. Reckoning in the thoracic legs, therefore, the true caterpillars have altogether five to eight, the false caterpillars nine to eleven pairs. The head of the latter is more rounded, while that of the former is more flattened. The way in which caterpillars walk depends upon the number of their legs. If this is fairly large so that most of the segments of the body are provided with legs, the whole body remains tolerably extended during progression. But if the number is small—as in the looper caterpillars, where there are three pairs of thoracic legs at the anterior end, and at the posterior end only a terminal pair of legs (the caudal pro-legs) and another pair in front of them—the middle legless region is strongly bent during locomotion (Fig. 63). Hence the name “looper.” The loopers often bend their bodies in a characteristic way. When at rest the hinder part is coiled up spirally; but as soon as the animals are alarmed they throw the hinder part of the body upwards and forwards and even over the head. The _grubs_ (Figs. 66 and 69, _left_) have indeed, like the caterpillars, a clearly visible hard head, but no characteristic abdominal legs, or at most a pair of sucker feet at the end of the body (wireworms). Thoracic legs are present in several grubs (cockchafer larvæ, wireworms, leaf beetles); in others (larvæ of weevils and fleas) they are entirely absent. _Maggots_ are those entirely footless insect larvæ which do not possess a head clearly marked off from the rest of the body, and the head-end of which is only to be recognized by the presence of the mouth and mouth-parts. _Pupæ_ are enclosed in a case which either only faintly indicates the outline of the various parts of the adult insect, or else closely surrounds every part of the body—wings, legs, antennæ, and even the mouth-parts and eyes. Pupæ of the first kind are termed _obtectate_ (Fig. 60); those of the second, _free_ (Figs. 61, 65).

Many pupæ are _naked_, others are surrounded by a web (cocoon) spun by the larva (Fig. 60). There are also pupæ distinguished by the peculiarity that when the insect has lived through the maggot-stage it does not strip off its integument, but turns into a pupa inside the shrivelled maggot-skin, from which the perfect insect later on breaks out (Fig. 67).

The class of insects can be divided into eleven orders: (1) _Coleoptera_ (Beetles); (2) _Orthoptera_ (Grasshoppers, Locusts); (3) _Neuroptera_ (Dragon-flies); (4) _Hymenoptera_ (Bees, Ants, Saw-flies); (5) _Lepidoptera_ (Butterflies and Moths); (6) _Hemiptera_ (Aphides, Bugs); (7) _Physopoda_ (Thrips); (8) _Diptera_ (Flies with two wings); (9) _Aphaniptera_ (Fleas); (10) _Pediculina_ (Lice); (11) _Collembola_ (Spring-tails and Tassel-tails).

ORDER I.: =Coleoptera= (BEETLES).

Beetles (Fig. 65) are insects with biting mouth-parts, and strongly developed prothorax united with the mesothorax so as to permit free movement. The fore wings are in the form of hard covers, leaving exposed only the head, neck-shield (_i.e._ the dorsal side of the prothorax), a three-cornered bit of the mesothorax (_scutellum_), and sometimes the tip of the abdomen. Flight is effected by the hind wings alone, which in a state of rest are drawn back under the wing-covers. The metamorphosis is complete; the larvæ are legless, or with thoracic legs only, and have a hard head with biting mouth-parts; change into free pupæ (p. 93).

Family: =Carabidæ= (_Ground Beetles_).

Usually elongated, slender; with long slender legs, five-jointed tarsi, eleven-jointed antennæ, powerful jaws (Figs. 68, 69). Run rapidly; usually keep on the ground; hide themselves during the day, but are very active at night; with very few exceptions feed entirely on other insects; when touched squirt an acrid stinking fluid out of the abdomen. Larvæ longish, six-legged, with short antennæ and sharp jaws, with a few exceptions live exclusively on other insects and lower animals.

Several species are of service, both in the adult and larval conditions, since they destroy injurious insects, _e.g._ surface caterpillars, wireworms, cockchafers, grubs, crane-fly larvæ. The following do good in cultivated fields: =Golden Ground Beetle= (_Carabus auratus_), =Garden Ground Beetle= (_C. hortensis_), =Granulated Ground Beetle= (_C. granulatus_), =Cross-barred Ground Beetle= (_C. cancellatus_), =Field Ground Beetle= (_C. nemoralis_), =Large-headed Ground Beetle= (_Cephalotes vulgaris_), species of _Harpalus_, _Pterostichus_, etc.

[Illustration:

FIG. 68.—A Ground Beetle (_Carabus auronitens_). ]

[Illustration:

FIG. 69.—Corn Ground Beetle (_Zabrus gibbus_) and larva. ]

The only destructive form is the =Corn Ground Beetle= (_Zabrus gibbus_, Fig. 69); short, thick-set; back black; belly, legs, and antennæ dark brown. Larva cylindrical, slightly hairy, brown, with yellowish white belly; head broad and flattened, black. The beetles (June, July) usually remain hidden in the soil during the day, climbing up the stalks of barley, wheat, and rye during the evening and in dull weather, and eating the grain in the ear. The larvæ remain during the day in vertical holes which they dig out; but at night and during dull weather they devour the overground parts of the grain-plants mentioned above, especially the hearts of young plants. They are destructive both in autumn and spring, damaging winter and summer grain. The larval condition is maintained for three years, the animal then turning into a pupa during July. Its ravages are limited to special years. _Remedy_: Sowing oats, peas, or vetches, or planting potatoes in fields infested by the beetles or their larvæ; collecting the beetles in the evening when they are in the ears.

Family: =Staphylinidæ= (_Rove Beetles_).

[Illustration:

FIG. 70.—Rove Beetle (_Staphylinus erythropterus_). ]

[Illustration:

FIG. 71.—The Black Burying Beetle (_Silpha atrata_) and larva. ]

Usually elongated, small (Fig. 70). The short truncated wing-covers leave the whole of the abdomen exposed. The rove beetles resemble the earwigs in their appearance and in a way they have of frequently lifting up the hinder end of the body and turning it forwards. Tarsi five-jointed, jaws strongly developed. The six-legged larvæ resemble those of the ground beetles, but have a relatively large head. The beetles live through the winter; the metamorphosis takes place in autumn. Live on the ground under fallen leaves, also under the bark of trees; in carcases. Some chiefly eat insects living in the soil and noxious insects; others, dung and decomposing matter. (Species of _Staphylinus_, and of _Ocypus_, e.g. _O. olens_, the =Devil’s Coach Horse=.) Several are of service. A few devour the parts of plants. _Anthobium torquatum_ is found in large numbers in the flowers of rape, devouring the petals, stamens, and pollen.

Family: =Silphidæ= (_Burying_, or _Sexton Beetles_).

The antennæ either thicken gradually or have only the end-joints larger; body flat; head projecting; tarsi five-jointed. The burying beetles and their larvæ feed on dead animals. A few (sp. of _Necrophorus_) bury the whole animal in the earth, and lay their eggs in it. Failing carrion, some of them can live on vegetable food; these sometimes do harm. Others prefer living insects and snails. They are of service in the economy of nature by doing away with stinking bodies. The following are sometimes harmful: =Black Burying Beetle= (_Silpha atrata_, Fig. 71), the larvæ of which often do much damage in fields of beetroot; _Silpha opaca_ (=Beet Carrion Beetle=), and _S. reticulata_, which, in the adult condition, may do harm to several kinds of plants. Remedies need not be considered, as it is only rarely they increase so largely as to make the supply of carrion insufficient, and consequently attack plants.

Family: =Nitidulidæ= (_Shine Beetles_).

Small. Antennæ club-shaped, eleven-jointed. Tarsi five-jointed. A few species live on carrion and on fungi, others under the bark of trees, a few in flowers. To these last belongs the =Turnip Flower Beetle= (_Meligethes æneus_); somewhat convex, elongated oval; shining metallic greenish black, finely dotted. Occurs in the inflorescences of turnip, rape, and allied species; also in the flowers of mustard, charlock, and similar crucifers, and species of buttercup (_Ranunculus_). At the beginning of spring, the turnip-flower beetle bores into the buds of turnip, rape, etc., and, later on, attacks the flowers. It perforates the petals, devours the stamens and pollen, and, lastly, the pistil. The infested flowers wither. Three to four beetles are often found in a single flower. The female soon lays her eggs, separately, in the ovary of the flower. One to two weeks later the larvæ may be found in the flowers, one or more in each. The larvæ, one-fiftieth of an inch long to begin with, are, when ready to become pupæ, about one-fifth of an inch long, cylindrical, yellowish white with blackish brown head; they have three pairs of short thoracic legs, as well as a pair of caudal pro-legs. Each segment of the body has two dark blotches on its upper side. On an average, the larvæ reach their full size in four to five weeks. They are first found at the bottom of the flower, where they gnaw the stamens and ovary. They then wander from flower to flower, until ready to become pupæ. If there are no more flowers in the neighbourhood they attack the developing pods, first gnaw the green husk, then bore through it and devour the young seeds. Become pupæ in the soil. The beetle emerges after a fourteen days’ pupa rest. At least two, usually three, sometimes four generations. _Remedy_: Rooting out charlock and the species of buttercup. Selection of strongly growing varieties of turnip, rape, etc., which blossom late (and therefore soon finish blooming). Drill-culture.

Family: =Cryptophagidæ= (_Secret_-_eating Beetles_).

Very minute. Antennæ composed of eleven joints, of which the three last form a club. Legs wide apart; tarsi five-jointed. Live in flowers, fungi, dead parts of plants, under bark, in the earth, in humblebees’ and ants’ nests, etc. The =Beet Beetle= (_Atomaria linearis_) is harmful: longish, egg-shaped, strongly convex; neck-shield as long as broad. Brownish black or dark brown. In fields where beet is cultivated for several years in succession, the beetles often increase in a prodigious way. They attack the seedlings, and devour the base of the stalk just below the surface of the soil, sometimes biting it half through. The attacked seedlings often die even before the cotyledons appear above the surface of the soil. Looking, therefore, in spring at fields infested by the beet beetle, the seedlings will appear quite normally developed in some few places, while in some other places there may be no plants at all: in many spots, again, small plants will be seen bearing only seed-leaves, withered and yellow. These cannot be pulled out of the ground, for they break off at the place gnawed by the beetle. It is often necessary to give two or three successive sowings, as the young crop is attacked again and again. The larva of the beet beetle is still unknown, though this undoubtedly develops in the beet-fields. _Remedy_: Suitable rotation. When the conditions will not permit this, the seed must be sown thickly, so that as many seedlings as possible may remain sound, should the beetles exert their destructive influence in the spring.

Family: =Lamellicornia= (_Chafers_).

[Illustration:

FIG. 72.—_a_, Antennæ of male; _b_, of female Cockchafer. ]

Body strong, stout (Fig. 65). The first joints of the antennæ have the usual shape; the last, three to seven, are very short, but broadened out on the inner side into leaf-like appendages, so that the end of the antennæ is fan-shaped (Fig. 72). The little leaves are laid together when at rest, so as to form a club-shaped thickened end; in flight, and when the attention of the beetle is excited, they are spread out like a fan. Legs strong; feet five-jointed. Flight rapid, somewhat awkward. Larvæ thick; body cylindrical, but curved; head hard, brown; rest of the body thin-skinned and yellowish white. The first three segments of the body bear legs. The curved larvæ can move about in the soil, but not on the surface. The beetles and larvæ devour vegetable substances; a comparatively small number of species feed on dung.

[Illustration:

FIG. 73.—_a_, abdomen of Common; _b_, of Horse-chestnut Cockchafer. ]

The =Common Cockchafer= (_Melolontha vulgaris_) will serve as a type of the lamellicorns (Fig. 65). The last segment of the body forms a gradually tapering process. The club of the antennæ with seven large leaflets in the male, and six smaller leaflets in the female (Fig. 72). Head, neck-shield, entire ventral surface, and legs, black; although these parts, with the exception of the head, may be reddish brown. Many specimens are thickly clothed with numerous white hairs; others are almost hairless. The beetles usually appear during May, but sometimes by mid April, and sometimes not till the beginning of June. In the evening they leave the soil and seek the neighbouring trees. They devour the leaves and especially the buds of oak, horse-chestnut, beech, poplar, willow, cherry, and other forest and fruit trees, but spare the lime and generally the morel cherry. Of coniferous trees it only devours the needles of larch and the young shoots of pine. Among cabbage-like plants it only devours rape. In “chafer years” the cockchafer becomes a veritable scourge to the farmer. For the purpose of laying her eggs (about forty in number), the female selects by preference a fertile soil rich in humus, but will also put up with a dry sandy soil. The grubs devour the grass and clover-roots in meadows, and, in cultivated fields, the roots of grain-plants, peas, and beans, rape, cabbage, etc., also turnips and potatoes; in gardens the roots of many vegetables and flowers, and, in particular, the underground parts of strawberry plants. If, on poor sandy soil, they can get nothing else, they devour the bark of oak and fir. Cockchafers take three to four years for their development: four in England, North Germany, and Central Germany; three in South France, Switzerland, the Rhine district, and Holland. In regions where the insect is abundant, every third or fourth year is a “chaferyear,” when the beetles appear in millions, while scarcely a cockchafer can be found in the intervening years. In districts less infested there is not the same marked distinction. It therefore appears that cockchafers and their larvæ are to be reckoned as injurious insects: their occurrence, however, is local. _Natural enemies_: moles, shrews, bats, foxes, crow-like birds, starlings, sparrows, owls, and the large species of ground-beetle. Winter floods do no harm to the grubs, which are then deep in the ground,—but this is not the case with floods occurring in summer, when they are near the surface eating the roots of the plants. _Remedies_: Collecting the grubs turned up during ploughing. Catching the cockchafers; this is very expensive, since it has to be done very energetically if most of them have left the pupastage. A part of the expense may, however, be recouped by using the cockchafers as manure.

The =Horse-chestnut Cockchafer= (_Melolontha hippocastani_) has a short slender caudal process, somewhat broader at the tip (Fig. 73). Its habits are in no way different from those of the preceding species.

The =Buckwheat Beetle= (_Phyllopertha horticola_), one-third to one-fifth of an inch long, without a caudal process. Shining blackish green, with yellowish brown elytra. Dark-coloured specimens are also found. The beetles appear in June; in some years they occur, like cockchafers, in large numbers. Habits of the beetle and of the small grub not markedly different from those of the cockchafer.

The =Rye Chafer= (_Anisoplia fruticola_), somewhat larger than the buckwheat beetle, in other respects very like it, but with a snout-like projection of the thickened skin of the head. Dark bronzy green, whitish on the under side. Wing-covers yellowish brown. On poor sandy soil, on the flowering ears of rye. The beetles gnaw the flowers.

[The =Garden Chafer= (_Anisoplia horticola_) is closely related to the preceding. The grub is very harmful to pastures.]

Family: =Elateridæ= (_Click Beetles_).

[Illustration:

FIG. 74.—The Skipjack (_Agriotes lineatus_): 1, magnified larva, below it the under side of the tip of the abdomen and the larva, natural size; 2, the beetle; 3, under side of the head of the larva, strongly magnified. _a_, maxilla; _b_, lower lip; _d_, labial palp; _e_, _k_, inner and outer maxillary palps; _f_, antennæ. ]

The Click Beetles (Fig. 74) are longish, of equal breadth all along, tolerably blunt at the hind end. Neck-shield strongly developed. Antennæ “serrated,” _i.e._ made up of three-cornered joints. Feet five-jointed. Looking at the under side a spine may be seen on the hinder margin of the prothorax (Fig. 75, _b_), and on the mesothorax (_c_) a furrow which receives the spine when the body is extended, but the spine is drawn out of it if the prothorax and mesothorax are lifted up from anything they happen to rest on (Fig. 75). A skipjack that has fallen upon its back first draws its antennæ and legs close to its body, and then bends this in such a way that the head and prothorax make an angle with the rest of the thorax and the abdomen. In this way the junction of the prothorax and mesothorax is lifted up, and the spine drawn as far as possible out of the furrow. As soon as the beetle has taken up this attitude, it can spring back into its usual position by lifting the two ends of the body and pressing the spine forcibly back into the furrow, whereby it is jerked against the ground with such a shock that its elasticity makes it spring into the air, where it turns round and comes down again ventral side below. The larvæ (“wireworms,” Fig. 74, 1) are like meal-worms, elongated, always flattened on the ventral side, and sometimes on the dorsal side as well. The head is dark brown, the twelve remaining segments of the body yellow to yellowish brown; the first three segments of the body bear three pairs of very small legs; the last segment has a pair of caudal pro-legs.

[Illustration:

FIG. 75.—A Skipjack lying on its back and about to spring up. _a_, head; _b_, spine of the prothorax; _c_, mesothorax; _d_, metathorax; _e_, abdomen. ]

[Illustration:

FIG. 76.—Grain-plants sown deep and shallow; a wireworm is devouring the underground part of the stem of the first. ]

Many species of click beetle are quite harmless, since they only devour decaying vegetable matter, either in humus or in the rotting substance of dying trees. There are also species, however, the larvæ of which feed on the living roots of plants. The wireworms of _Lacon murinus_, which are tolerably thick and have a flattened tip to the abdomen, devour the roots of fruit trees, rose-bushes, various vegetables (lettuce, cabbage, onions, turnips) and flowers; they are principally to be found in garden soils rich in humus. The relatively small hairless wireworms which do great damage, especially to grain-plants, but also to potatoes, carrots, turnips, rape, hops, and almost all the plants of our arable land, belong to _Agriotes lineatus_ or _A. obscurus_; the larger and more hairy wireworms destructive in cultivated land almost all belong to _Athous hæmorrhoidalis_ or a related species. The species named above also do much damage in meadows and grass land. Those fields are most infested which bore grass or clover the preceding year. Wireworms are usually more destructive in dry soil than in wet. They devour all underground parts, but specially prefer fleshy organs (potatoes, turnips), as well as the underground stem-parts of grain-plants, working themselves up from the soil into the inside of the lower part of the haulm, where they destroy the plant by gnawing its base. They also often destroy, in young grain-plants, the region of the stem which extends from the remains of the seed to the surface (Fig. 76, _left_). In both cases the plant is killed by the wireworms; the injuring of the roots is less fatal. It is obvious that in shallow sowing only a small piece of underground stem is exposed to the attacks of wireworms, in deep sowing a much larger piece; besides this, a plant which has been sown shallow develops earlier a strong mass of roots, and in its young state can therefore offer a greater resistance to the destructive influence. Since wireworms require four or five years for their development, the same field is infested by them the whole year. The greatest damage is done in spring and autumn. When wireworms have gnawed into the lower part of the haulm, the lower leaves first turn yellow, and the death of the whole plant soon follows. _Remedies_: Repeated ploughing of fields infested by wireworms, so that rooks, starlings, wagtails, gulls, etc., can devour them. Perhaps, too, many larvæ are frozen. Sowing the seed as shallow as possible on infested fields (Fig. 76). Waste potatoes may be used as a means of drawing them from the crop.

Family: =Curculionidæ= (_Weevils_).

Most species are small. Head lengthened into a proboscis (Fig. 79, 3); the jaws are found at the front end of the proboscis, the eyes at its base. The antennæ, which in most species are bent like a knee, and are always thickened at the tip, are attached to the front end, middle, or hinder end of the proboscis. The wing-covers usually extend to the tip of the abdomen, and clasp it in several species. Feet four-jointed. Weevils are mostly sluggish; many kinds do not fly at all; others only during the breeding season. When disturbed they let themselves fall to the ground as if dead. Almost without exception the females lay their eggs within plants, boring a hole by means of their proboscis, and shoving in the egg. The whitish larvæ (Fig. 66) are more or less curved and limbless, with hard brownish heads.

[Illustration:

FIG. 77.—The Bean Beetle (_Bruchus rufimanus_) and beans gnawed by it. ]

The =Seed Beetles= (_Bruchus_) have a very short snout. Body short, thick-set, almost four-cornered. The wing-covers leave the hinder part of the body exposed. The female lays her eggs in the seeds of leguminous plants. The larva hollows out one or several, becoming a pupa in the one last inhabited. Here belong the =Pea Beetle= (_B. pisi_), the two =Bean Beetles= (_B. rufimanus_ and _B. granarius_), of which the last-named also lives in vetches and chickling peas, and the =Lentil Beetle= (_B. lentis_). The =Pea Beetle= (_B. pisi_) is black, with brown hairy covering flecked with white. Like all other species of seed beetle, it becomes a pupa in the last seed inhabited by the larva, and the pupa changes into a beetle in autumn. A pea inhabited by such an insect can be recognized by a black translucent patch, since the beetle has become a pupa immediately under the seed-coat. Late the following spring the beetle crawls out. As the beetles are usually still in the peas at the time of sowing, the process brings them into the fields. Later on, when the beetles crawl out, they lay their eggs in the ovaries of the flowers of the pea-plants, which have meanwhile developed. The _remedies_ are, consequently,—late sowing of the peas, or killing the beetles in them by exposure (for two minutes) to a temperature of 122° Fahr., or for ten minutes to sulphur dioxide fumes in a closed space. The remaining three species of Bruchus have the same habits as the bean beetle, but the insect often creeps out much earlier, so that the seeds do not require treatment.

[Illustration: