Part 11

_Poison-secretor_ (_Ioterium_). This organ, which is most conspicuous in the _Hymenoptera_ Order, has not received much notice, except in the case of the Hive-bee and the _Scolia_: in the former, it is an elliptical membranous vesicle or reservoir, furnished at its lower extremity with a tube which renders to the sting, and at the other by a blind, long, filiform, secretory, vessel, which according to Swammerdam divides into _two_ terminal blind branches[620], though Reaumur could detect but _one_[621]; in this vessel the poison is secreted and stored up. In _Scolia_ there are two secretory vessels, which enter the reservoir in the middle on each side[622]. In the _Scorpion_, we learn from Marcel de Serres that the poison-secretor is clothed externally with a horny thickish membrane, containing two yellowish glands, composed of an infinity of spherical glandules, terminating in a canal, enlarged towards its base so as to form a reservoir, and leading to the extremity of the sting[623]. Connected by a slender tube with each mandible in _spiders_ is a vessel with spiral folds, which seems properly to belong to _this_ head--though Treviranus calls it a _saliva_-vessel[624]--since in the _Mygale avicularia_ and other spiders, the effect of the bite is said to be so venomous as to occasion considerable inflammation, and sometimes death[625].

v. _Scent-secretors_ (_Osmateria_). Amongst other means with which insects are gifted for the annoyance of their foes and pursuers, are the powerful _scents_ which many of them emit when alarmed and in danger. Concerning the _internal_ organs by which these effluvia are _secreted_ we possess but little information, but more notice has been taken of the _external_ ones by which they are _emitted_. We may conclude in general, that the secretory organs are membranous sacs or vesicles, perhaps terminating in longer or shorter blind filiform vessels, sometimes secreting a fetid fluid, and at others a fetid gaseous effluvium. The _Iulidæ_, at least _Iulus_ and _Porcellio_[626], cover themselves when alarmed, with a _fluid_ of this kind, or emit one, for this faculty is not peculiar to the species noticed by Savi. I observed early in the year, when I handled _Iulus terrestris_, that it was covered with a slimy secretion, of a powerful scent, which stained my fingers of an orange colour. The spiraculiform pores that mark the sides of the animal are the outlets by which this fluid is emitted, and not spiracles as has been supposed: each of these orifices, as we learn from Savi, terminates internally in a black vesicle, which is the reservoir of the fluid[627]. The most remarkable insect for its powers of annoyance in this way, is one on that account called the _bombardier_ (_Brachinus crepitans_), which can fire numerous volleys of stinking vapour at its assailants before its ammunition is exhausted[628]. M. Dufour has given a very particular account of the organ that secretes this vapour;--it consists of a double apparatus, one on each side, in the cavity of the abdomen, both formed of two distinct vessels. The _first_, which is the innermost, presents itself under two different aspects, according as it is contracted or dilated: in the former case it is a whitish, irregularly rounded, soft body, apparently glandular, placed under the last abdominal segments; communicating at one end with the reservoir, and terminating constantly at the other in a very long and slender filament: in the second case, or when it is dilated, it resembles an oblong, membranous, diaphanous sac, filled with air, then occupying the whole length of the abdomen, and appearing free except where it communicates with the reservoir. The _second_ vessel or reservoir is a small, spherical, brown or reddish body, constant in its form, internally hollow, placed under the last dorsal segment, precisely above the _rectum_, and opening by a small pore into the _anus_[629]: so that the tail of this little beetle may be regarded as a battery mounted with two pieces of cannon, which our alert bombardier fires alternately without intermission till all his ammunition is expended. The ground-beetles (_Eutrech_in_a_) in general have a pair of these anal scent-secretors, which discharge an acrid and caustic fluid, and sometimes a volatile one[630]. The external organ of the scent-secretors in _Gyrinus_ consists of two minute hairy cylindrical retractile tubes, of a red colour[631]. Numerous insects of other tribes and genera emit _scents_ from their anus, and from various other parts of the body, of which having before given you a very full account[632], I shall proceed to the consideration of the secretions themselves: but first I must observe, that in many cases, as in some of the cottony and powdery _Aphides_, _Chermes_, &c., the substance secreted appears to be a transpiration through the pores of the body, a kind of excretion from the superabundance of its fluid contents[633]. In many, however, this secretion transpires through appropriate orifices: thus in _Chermes Abietis_, which produces those curious galls resembling the cone of a fir[634], the flocoons of seeming cotton that cover it proceed from little oval concavities on its back, four of which are arranged in a transverse line on each dorsal segment of the abdomen: these concavities have minute tubercles probably terminating in a pore[635]. In _Aphis Fagi_ the cottony flocoons are almost an inch long[636].

* * * * *

The _secretions_ of insects may be considered under the following heads--_Silk_; _Saliva_; _Varnish_ or _Gum_; _Jelly_; _Oils_; _Milk_; _Honey_; _Wax_; _Poisons_ and _Acids_; _Odorous fluids_ and _Vapours_; and _Luminous matter_.

i. _Silk._ This valuable product of insects, while in the silk-secretor, assumes in the _Lepidoptera_ the appearance of a viscid gum, but the moment it is exposed to the air it hardens into a silken thread. It is remarkable for the following qualities:--it dries the instant it comes in contact with the air; it is then insoluble not only in water but in the most active solvents, and even _heat_ has no effect upon it to melt or soften it: indeed, without these qualities it would be of no use to us[637]. As soon as it leaves the spinneret it becomes the thread we call silk, which being drawn through _two_ orifices is necessarily _double_ through its whole length. This thread varies considerably in colour and texture, as has been before stated[638], and sometimes resembles cotton or wool rather than silk. In spiders it is of a much softer and more tender texture than that of other spinning insects; and Mr. Murray seems to have proved that it is imbued, in the case of the gossamer, with negative electricity: in the _sericterium_ the fluid that produces it is sometimes white or grey, and at others yellow[639]. A remarkable gnat (_Ceroplatus tipuloides_), living on an agaric, carpets its station of repose and its paths with something between silk and varnish, which it spins, not in a _thread_, but in a _broad_ riband[640].

ii. _Saliva._ Many insects have the power of discharging from their mouth a fluid which seems in some degree analogous to the _saliva_ of larger animals. Thus many, as _Lepidoptera_, _Hemiptera_, _Diptera_, &c., can dilute their food, and render it fitter for deglutition. I have seen a common fly when not employed in eating, emit a globule of fluid as big as a grain of mustard-seed from its proboscis, and retract it again. On a former occasion I observed to you that many predaceous, carnivorous, and some herbivorous beetles, when alarmed emit a drop of coloured acrid fluid from the mouth[641]. That this is not secreted in any of the ordinary salival vessels is evident from Ramdohr's dissections of those beetles[642], who, had there been such an organ, would doubtless have discovered it: but as the stomach of all of them is distinguished by those minute _cœca_ or blind vessels, which he denominates shags (_zotten_)[643], perhaps these may be the secretors of this fluid, probably analogous to the gastric juice[644]; in which case its _primary_ office would be the _digestion_ of the food. We are not however warranted in considering _every_ fluid effused from the mouth as saliva. The glutinous material with which wasps cement the woody fibres for their paper edifices[645]; that with which some sand-wasps moisten the sand which they scrape away, of which they form the singular tubes that lead to their nests[646]; and that with which the aphidivorous larvæ fix themselves previously to their becoming pupæ[647],--may be a secretion distinct from saliva; possibly intermediate between it and gum or the matter of silk, and secreted by peculiar organs. In the wasp, however, Ramdohr discovered nothing of the kind[648]; and in _Syrphus_, as before observed, the saliva-secretors are very peculiar in their structure, as if appropriated to the secretion of a peculiar fluid[649]. Something similar has been observed by Reaumur with regard to the larva of _Crioceris merdigera_, which forms its cocoon with a kind of froth produced from the mouth[650].

iii. _Varnish_ or _Gum_. The eggs of various insects, when they leave the oviduct, are covered with a kind of varnish or gum by which they adhere to the substances that the young larvæ are to feed upon, or are placed in a proper position for their hatching in an appropriate station. Several instances of this have been already mentioned[651]; I shall therefore not enlarge further upon the subject. With regard to the secretion itself, little has been recorded except its _colour_, which has been before noticed. Some _Lepidoptera_ also as we learn from Reaumur and Bonnet[652], use a varnish in the construction of their cocoons.

iv. _Jelly_ or _Gluten_. This secretion is particularly conspicuous in the _Trichoptera_ and some _Diptera_, serving as a bed or _nidus_ for those eggs that are committed to the water,--upon which I have nothing to add to what has been before said[653]. Under this head also may be noticed the fluid, secreted in peculiar vesicles, that lubricates the oviduct and the passages of the sexual organs[654].

v. _Oils._ Oily substances are sometimes produced by insects. The common oil-beetle (_Meloe Proscarabæus_) when touched sends forth a drop of this kind of fluid, of an orange colour, from each joint of its legs[655]: something similar I have observed in _Coccinella bipunctata_: Ray mentions a locust taken in Spain which emits a yellow oleaginous fluid from between the claws of its fore legs[656]; but the precise nature of these substances has not been ascertained, nor whether they are secreted by peculiar organs.

vi. _Milk._ A milky fluid is produced by the larva of _Chrysomela Populi_. Willughby observed a similar effusion from pores in the upper surface of the body of _Acilius sulcatus_; and other insects emit it from other parts of their body[657].

vii. _Honey._ It is certain that honey is not an _animal_ secretion; yet the saccharine matter collected from the nectaries of flowers, from which it is derived, seems to undergo some _alteration_ in the stomach; for the consistence of honey is greater than that of any vegetable nectar, and its taste does not vary greatly, while that of the nectar in different plants is probably not the same. Reaumur also has observed, that each honey-cell in a bee-hive is always covered by a cream-like layer of a thicker consistence than the rest, which apparently serves to prevent the more liquid honey, which from time to time is introduced under it, from running out[658]. Now if honey were the unaltered nectar of plants, it is difficult to conceive how this cream could be collected in proper proportions. The last-mentioned naturalist likewise ascertained, that if bees, in a season in which the fields afford a scarcity of food, be supplied with _sugar_, they will from this substance fill their cells with _honey_ which differs in no respect from the common sort, except that its flavour is a little heightened[659]:--a similar argument may be deduced from the circumstance of the bees imbibing the juices of _fruits_ of various kinds as they are well known to do[660]. It seems therefore evident that the honey collected by bees undergoes some modification in their honey-stomach before it is regurgitated into the cells, and therefore may be regarded in some degree as a peculiar secretion.

Huber says that he has ascertained by a great number of observations that electricity is singularly favourable to the secretion of the substance of which honey is formed by flowers; the bees never collect it in greater abundance, nor is the formation of wax ever more

## active, than when the wind is in the south, the air humid and warm,

and a storm gathering[661].

viii. _Wax_ generally transpires through the pores of the skin of those insects that produce it, either partially or generally, and it is secreted from honey or other saccharine substances taken into the stomach. In the hive-bee, as has been before stated, it is produced _partially_[662], but in many other insects it is a _general_ transudation of the body. This is particularly the case with a large number of the _Homopterous Hemiptera_; and those flocoons that look like cotton, and cover the body of several _Chermes_ and _Aphides_, if closely examined will be found of the nature of _wax_: this I have

## particularly noticed with respect to _Chermes Fagi_, in which the

cotton-like flocoons are often so long as to cause the insect to look like a feather, and a leaf covered by them exhibits a very singular appearance, as if clothed with the fine down of a swan[663]. Probably the white powder or threads that appear to transpire through the skin of many other insects is of a waxy nature. In the larva of a beetle described by Reaumur, the flocoons are so arranged as to give the animal some resemblance to a hedgehog, and when rubbed off they are reproduced in twelve hours[664]. Gyllenhal, speaking of _Peltis limbata_, observes, that when alive it is covered with a white powder resembling mould, which if rubbed off returns again as long as the animal lives[665].

It will not be improper to include under this head what further account I have to give of _Lac_, which though regarded as a _resin_, since _Cocci_ sometimes certainly produce _wax_[666], probably has some analogy with the latter substance. When the females of this _Coccus_ (_C. Lacca_) have fixed themselves to a part of the branch of the trees on which they feed (_Ficus religiosa_ and _indica_, _Butea frondosa_, and _Rhamnus Jujuba_[667]), a pellucid and glutinous substance begins to exude from the margins of the body, and in the end covers the whole insect with a cell of this substance, which when hardened by exposure to the air becomes lac. So numerous are these insects, and so closely crowded together, that they often entirely cover a branch; and the groups take different shapes, as squares, hexagons, &c., according to the space left round the insect which first began to form its cell. Under these cells the females deposit their eggs, which after a certain period are hatched, and the young ones eat their way out. Though indisputably an _animal_ secretion, many of the properties of lac are not very different from those of the juices of the trees on which the animal feeds, and which therefore would seem to undergo but little alteration.

Wax seems also to form a constituent part of some insects which are not found to secrete it. The yellow substance deposited in vessels containing _spiders_ in alcohol is said to be a true _wax_, and may be obtained from these animals by gently heating them[668].

ix. _Poisons_ and _Acids_. The _bite_ as well as the _sting_ of many insects is followed by inflamed tumours, so that the _sialisteria_ of some _bugs_, _Diptera_, _Aptera_ and _spiders_, may be regarded as producing a poisonous fluid; but we know nothing of the real nature of it, nor of that of other venomous insects, except the _ant_--whose celebrated _acid_ may be considered under the present head,--the _bee_, the _wasp_, and the _scorpion_.

Contrary to the once received doctrine that no _acid_ was to be found in any animal, except as the effect of disease in the alimentary canal, many insects secrete peculiar and powerful ones. I have on a former occasion related an instance in which an acid of this description, secreted in its _sialisteria_, is employed by a moth to soften its cocoon[669]; and Lister mentions a species of _Iulus_ which produced one resembling that of ants[670]; but this last is the most powerful of all. The fact that blue flowers when thrown into an ant-hill become tinged with red has been long known; but Mr. Fisher of Sheffield, about 1670, seems to have been the first who ascertained that this effect is caused by an _acid_ with which ants abound, and which may be obtained from them by distillation or infusion in water[671]. Margraff and other chemists confirmed this discovery[672]; and concluding that this acid was of a peculiar kind, they gave it the name of the _Formic acid_. This name, however, is now exploded; the subsequent experiments of Deyeux, Fourcroy and Vauquelin having ascertained that the acid of ants is not of a distinct kind, but a mixture of the _Acetic_ and _Malic_[673]. These acids are in such considerable quantities, and so concentrated in these animals, that, when a number of _Formica rufa_ are bruised in a mortar, the vapour is so sharp that it is scarcely possible to endure it at a short distance. It also transpires from them, for they leave traces of it on the bodies which they traverse: and hence, according to the experiments of Mr. Coleridge, the vulgar notion that ants cannot pass over a line of chalk is correct; the effervescence produced by the contact of the acid and alkaline being so considerable, as in some degree to burn their legs[674]. The circumstance of much of the food of ants being of a saccharine nature may account for this copious secretion of acid, the use of which is probably to defend themselves and their habitations from the attack and intrusion of their enemies: if a frog be put into a nest of _Formica rufa_ that has been deranged, it will be suffocated in five minutes[675]. That which they _ejaculate_ from their _anus_ when attacked, as formerly stated[676], must be secreted in an _ioterium_; but their very _blood_ seems of an acid nature. It is very probable, as Dr. Thomson has observed[677], that acids may be obtained from many other insects, and that they are various modifications of the acetic.

From the circumstance that water is absorbed by _greasy_ moths, that crystals of a salt are occasionally found adhering to them, that they change blue litmus paper _red_,--it has been inferred that their supposed _oiliness_ is in fact an _acid_ or acid salt, having the property of attracting moisture from the air, the infected moths being in fact not greasy, but _wet_; hence the application of chalk and clay, usually recommended in this case, can have only a temporary and superficial effect. The only effectual remedy, is steeping the body in spirits of wine till all the acid is extracted[678]. This acid is probably the same as Chaussier obtained from silkworms, since called _Bombic Acid_[679].

The _poison_ of _bees_ and _wasps_, as to its chemical qualities, is a transparent fluid, at first sweet to the taste, but immediately afterwards hot and acrid like the milky juice of the _spurge_[680]; soluble in water, but not in alcohol; and separable from the former in the state of white powder, when the latter is added giving a slight _red_ tinge to paper stained with vegetable blue, and when dry and chewed appearing tenacious, gummy and elastic. This last property, as well as solubility in water and not in alcohol, is common also to the poison of the _viper_, which however differs in being tasteless, and not affecting vegetable blues. From hence Fontana concludes that this fluid is united with an _acid_, but in a very small proportion, and not with an _alkali_[681]. The venom of bees is extremely active; a grain in weight, it is conjectured, would kill a pigeon in a few seconds[682]. It is remarkable, however, that while in some constitutions the sting of a single bee or wasp is sufficient sometimes to induce alarming symptoms, in others numerous punctures will produce little or no pain or inflammation. That this fluid, and not the puncture of the sting, is the sole cause of the inflammation that usually follows the wound inflicted by one of these animals, is proved by the facts, that if it be introduced into one made by a needle, the same effect ensues, and that when the whole contents of the poison-bag have been exhausted by the insect's stinging three or four times in succession, its weapon then becomes harmless[683].

The venom of _scorpions_, though much more potent, probably resembles that of bees, &c., in many of its chemical qualities: it issues from two pores in the sting before described[684], where, when the animal is irritated, it accumulates under the form of two little drops of a whitish colour: spread upon paper this fluid produces a spot like what would be caused by oil or grease, and this part of the paper becomes by desiccation firmer and transparent[685].

x. _Odorous fluids_ and _Vapours_[686]. The powerful scents which different insects emit are extremely numerous, much more so indeed than the generality of Entomologists have been aware, for there is scarcely a scent odious or agreeable that may not be met with in the insect world. This you will be convinced of, by following a practice which I would recommend to you--that of smelling the insects you take. Some of these scents are peculiar to particular parts or organs, and some are exhaled generally by the whole body; some are emitted by a fluid secretion, and others are gaseous effluvia. On a former occasion I gave you a rather full account of these scents and their organs[687]; I shall relate here only what I there omitted. To begin with _sweet_ odours. Many beetles emit an agreeable scent. The rose-scented Capricorn or musk-beetle (_Cerambyx moschatus_) has long been noted for the delicious scent of roses which it exhales; this is so powerful as to fill a whole apartment, and the insect retains it long after its death. Captain Hancock also informed me that another species of the same genus, _C. sericeus_, has in a high degree a scent resembling that of the cedar[688] on which they feed. Though most of the micropterous tribes (_Brachyptera_) have a _fetid_ smell, yet there are some exceptions to this amongst them. One species (_Philonthus suaveolens_ K. MS.) related to _P. micans_, which I once took, smelt precisely like a fine high-scented ripe pear; another, _Oxytelus morsitans_, like the water-lily; a third, _O. rugosus_, like water-cresses; and lastly, a fourth (_P. fuscipes_) like saffron[689]: _Trichius Eremita_, one of the Petalocerous beetles, is stated to have the scent of Russia leather; _Geotrupes vernalis_, in spite of its stercorarious food, of lavender-water[690]. Mr. Sheppard has observed that _Dytiscus marginalis_ when recently taken smells not unlike liquorice: Bonnet mentions a caterpillar that had the scent of new hay. A little gall-fly (_Cynips Quercus Ramuli_) has the remarkable odour of Fraxinella: the larva of another species of this genus (_C. Rosæ_) has an odour which seemed to Reaumur as attractive to cats as that of _Nepeta cataria_ or _Teucrium Marum_[691]: some _Phalangia_ smell like walnut leaves[692]; and the various species of the genus _Prosopis_ (_Melitta_ * b. K.) have a very agreeable scent of _Dracocephalum moldavicum_[692].