Some lepidopterous larvæ, that fix the one half of the body and elevate the other, agitate the elevated part, whether it be the head or the tail, as if to strike what disturbs them[329]. The giant caterpillar of a large North American moth (Ceracampa regalis) is armed behind the head and at the back of the anterior segments with seven or eight strong curved spines from half to three-fourths of an inch in length. Mr. Abbot tells us that this caterpillar is called in Virginia the hickory-horned devil, and that when disturbed it draws up its head, shaking or striking it from side to side; which attitude gives it so formidable an aspect, that no one, he affirms, will venture to handle it, people in general dreading it as much as a rattle-snake. When, to convince the Negroes that it was harmless, he himself took hold of this animal in their presence, they used to reply that it could not sting him, but would them[330]. The species of a genus of beetles named Malachius, endeavour to alarm their enemies and show their rage by puffing out and inflating four vesicles from the sides of their body, which are of a bright red, soft, and of an irregular shape. When the cause of alarm is removed, they are retracted, so that only a small portion of them appears[331].
Insects often endeavour to repel or escape from assailants by their motions. Mr. White, mentioning a wild bee that makes its nest on the summit of a remarkable hill near Lewes in Sussex, in the chalky soil, says: "When people approach the place these insects begin to be alarmed, and with a sharp and hostile sound dash and strike round the heads and faces of intruders. I have often been interrupted myself while contemplating the grandeur of the scenery around me, and have thought myself in danger of being stung[332]."—The hive-bee will sometimes have recourse to the same expedient, when her hive is approached too near, and thus give you notice what you may expect if you do not take her warning and retire.—Humble-bees when disturbed, whether out of the nest or in it, assume some very grotesque and at the same time threatening attitudes. If you put your finger to them, they will either successively or simultaneously lift up the three legs of one side; turn themselves upon their back; bend up their anus and show their sting accompanied by a drop of poison. Sometimes they will even spirt out that liquor. When in the nest, if it be attacked, they also beat their wings violently and emit a great hum[333].
These motions menace vengeance; those of some other insects are merely to effect their escape. Thus I have observed that the species of the May-fly tribe (Trichoptera[334]), when I have attempted to take them, have often glided away from under my hand—without moving their limbs that I could discover—in a remarkable manner. I once observed a short-snouted weevil (Brachyrhynchus, Schön.) upon a rail, which, when it saw me, slided sideways, and then rolled off. To notice the ordinary motions of insects, which are often means by which they escape from danger, would here be premature, since they will be fully considered in a subsequent letter. I shall therefore only mention the zigzag flight of butterflies and the traverse sailing of humble-bees, which certainly render it more difficult for the birds to catch them while on the wing.
Noises are another mean of defence to which insects have occasional recourse. I have heard the lunar dung-beetle (Copris lunaris) when disturbed utter a shrill sound. Dynastes Oromedon, another of the lamellicorn insects, was observed by Dr. Arnold to make, when alarmed, a kind of creaking noise, which it produced by rubbing its abdomen against its elytra. A third of the same tribe, (Trox sabulosus) emits a small sibilant or chirping noise, as I once observed when I found several feeding in a ram's horn. The "drowsy hum" of beetles, humble-bees, and other insects, in their flight, may tend to preserve them from some of their aërial assailants. And the angry chidings of the inhabitants of the hive, which are very distinguishable from their ordinary sounds, may be regarded as warning voices to those from whom they apprehend evil or an attack. I have before observed that the death's-head hawk-moth (Acherontia Atropos), when menaced by the stings of ten thousand bees enraged at her depredations upon their property, possesses the secret to disarm them of their fury[335]. This insect, when in fear or danger, is known to produce a sharp, shrill, mournful cry, which with the superstitious has added to the alarm produced by the symbol of death which signalizes its thorax[336]. This cry, there is reason to believe, affects and disarms the bees, so as to enable her to proceed in her spoliations with impunity[337]. One of these insects being once brought to a learned divine, who was also an entomologist, when he was unwell, he was so much moved by its plaintive noise, that, instead of devoting it to destruction, he gave the animal its life and liberty. I might say more upon this subject of defensive noises: but I shall reserve what I have further to communicate, to a letter which I purpose devoting to the sounds produced or emitted by insects.
You are acquainted with the singular property of the skunk (Viverra putorius, L.), which repels its assailants by the fetid vapour that it explodes; but perhaps are not aware that the Creator has endowed many insects with the same property and for the same purpose—some of which exhale powerful or disagreeable odours at all times, and from the general surface of their body; while they issue from others only through particular organs, and when they are attacked.
Of the former description of defensive scents there are numerous examples in almost every order; for, next to plants and vegetable substances, insects, of any part of the creation, afford the greatest diversity of odours. In the Coleoptera order a very common beetle, the whirlwig (Gyrinus Natator), will infect your finger for a long time with a disagreeable rancid smell; while two other species, G. minutus and villosus, are scentless.—Those unclean feeders, the carrion beetles (Silpha, L.), as might be expected from the nature of their food, are at the same time very fetid.—Pliny tells us of a Blatta,—which, from his description, is evidently the darkling-beetle (Blaps mortisaga), and which he recommends as an infallible nostrum, when applied with oil extracted from the cedar, in otherwise incurable ulcers,—that was an object of general disgust on account of its ill scent, a character which it still maintains[338].—Numbers of the ground-beetles (Eutrechina) that are found under stones, and in places that have not a free circulation of air, exhale a most disagreeable and penetrating odour, which De Geer observes resembles that of rancid butter, and is not soon got rid of. It is produced, he says, from an unctuous matter that transpires through the body[339]; but I am rather inclined to think it proceeds from the extremity.—I have noticed that some small beetles of the Omalium genus—for instance O. rivulare, and another species that I once found in abundance on the primrose (O. Primulæ, K. Ms.), especially the latter—are abominably fetid when taken, and that it requires more than one washing to free the fingers from it. Every one knows that the cock-roach (Blatta orientalis), belonging to the Orthoptera order, is not remarkable for a pleasant scent;—but none are more notorious for their bad character in this respect than the bug tribe (Geocorisæ), which almost universally exhale an odour that mixes with the scent of cucumbers another extremely unpleasant and annoying. Some however are less disgusting, particularly Lygæus Hyoscyami, which yields, De Geer found, an agreeable odour of thyme[340].—Several lepidopterous larvæ are defended by their ill smell; but I shall only particularize the silk-worms, which on that account are said to be unwholesome.—Phryganea grandis, a kind of May-fly, is a trichopterous insect that offends the nostrils in this way; but a worse is Chrysopa Perla, a golden-eyed and lace-winged fly, of the next order, whose beauty is counterbalanced by a strong scent of human ordure that proceeds from it.—Numberless Hymenoptera act upon the olfactory nerves by their ill or powerful effluvia. One of them, an ant (Formica fœtida De Geer, fœtens Oliv.), has the same smell with the insect last mentioned[341]. Our common black ant (F. fuliginosa), whose curious nests in trees have been before described to you[342], is an insect of a powerful and penetrating scent, which it imparts to every thing with which it comes in contact; and Fabricius distinguishes another (F. analis, Latr., fœtens, F.) by an epithet (fœtidissima) which sufficiently declares its properties. Many wild bees (Andrena) are distinguished by their pungent alliaceous smell. Crabro U. flavum, a wasp-like insect, is remarkable for the penetrating and spirituous effluvia of ether that it exhales[343]. Indeed there is scarcely any species in this order that has not a peculiar scent.—Some dipterous insects—though these in general neither offend nor delight us by it—are distinguished by their smell. Thus Mesembrina mystacea, a fly that in its grub state lives in cow-dung, savours in this respect, when a denizen of the air, of the substance in which it first drew breath[344]. And another (Sepsis cynipsea,) emits a fragrant odour of baum[345].—I have not much to tell you with respect to apterous insects, except that Iulus terrestris, a common millepede, leaves a strong and disagreeable scent upon the fingers when handled[346]. Most of the insects I have here enumerated, probably, are defended from some enemy or injury by the strong vapours that exhale from them; and perhaps some in the list produce it from particular organs not yet noticed.
I shall next beg your attention to those insects that emit their smell from particular organs. Of these, some are furnished with a kind of scent-vessels, which I shall call osmateria; while in others it issues from the intestines at the ordinary passage. In the former instance the organ is usually retractile within the body, being only exerted when it is used: it is generally a bifid vessel, something in the shape of the letter Y. Linné, in his generic character of the rove-beetles (Staphylinidæ), mentions two oblong vesicles as proper to this genus. These organs,—which are by no means common to the whole genus, even as restricted by late writers,—are its osmateria, and give forth the scent for which some species, particularly Ocypus brunnipes, are remarkable. If you press the abdomen hard, you will find that these vesicles are only branches from a common stem; and you may easily ascertain that the smell of this insect, which mixes something extremely fetid with a spicy odour, proceeds from their extremity.—A similar organ, half an inch in length, and of the same shape, issues from the neck of the caterpillar of the swallow-tail-butterfly (Papilio Machaon)[347]. When I pressed this caterpillar, says Bonnet, near its anterior part, it darted forth its horn as if it meant to prick me with it, directing it towards my fingers; but it withdrew it as soon as I left off pressing it. This horn smells strongly of fennel, and probably is employed by the insect, by means of its powerful scent, to drive away the flies and ichneumons that annoy it. A similar horn is protruded by the slimy larva of P. Anchises, as also Parnassius Apollo and many other Equites[348].—Another insect, the larva of a species of saw-fly described by De Geer, is furnished with osmateria, or scent-organs, of a different kind. They are situated between the five first pair of intermediate legs, which they exceed in size, and are perforated at the end like the rose of a watering-pot. If you touch the insect, they shoot out like the horns of a snail, and emit a most nauseous odour, which remains long upon the finger; but when the pressure is removed they are withdrawn within the body[349].—The grub of the poplar-beetle (Chrysomela Populi) also is remarkable for similar organs. On each of the nine intermediate dorsal segments of its body is a pair of black, elevated, conical tubercles, of a hard substance; from all of these when touched the animal emits a small drop of a white milky fluid, the smell of which, De Geer observes, is almost insupportable, being inexpressibly strong and penetrating. These drops proceed at the same instant from all the eighteen scent-organs; which forms a curious spectacle. The insect, however, does not waste this precious fluid: each drop instead of falling, after appearing for a moment and dispensing its perfume, is withdrawn again within its receptacle, till the pressure is repeated, when it reappears[350].
I shall now introduce you to the true counterparts of the skunk, which explode a most fetid vapour from the ordinary passage. I have lately hinted that the scent of many Eutrechina is thus emitted. Anchomenus prasinus, a beetle of this tribe, combats its enemies with repeated discharges of smoke and noise: but the most famous for their exploits in this way are those, which on this account are distinguished by the name of bombardiers (Brachinus). The most common species (B. crepitans), which is found occasionally in many parts of Britain, when pursued by its great enemy, Calosoma Inquisitor, seems at first to have no mode of escape: when suddenly a loud explosion is heard, and a blue smoke attended by a very disagreeable scent, is seen to proceed from its anus, which immediately stops the progress of its assailant: when it has recovered from the effect of it, and the pursuit is renewed, a second discharge again arrests its course. The bombardier can fire its artillery twenty times in succession if necessary, and so gain time to effect its escape.—Another species (B. Displosor) makes explosions similar to those of B. crepitans: when irritated it can give ten or twelve good discharges; but afterwards, instead of smoke it emits a yellow or brown fluid. By bending the joints of its abdomen it can direct its smoke to any particular point. M. Leon Dufour observes that this smoke has a strong and pungent odour, which has a striking analogy with that exhaled by the Nitric Acid. It is caustic, reddening white paper, and producing on the skin the sensation of burning, and forming red spots, which pass into brown, and though washed remain several days[351].
Another expedient to which insects have recourse to rid themselves of their enemies, is the emission of disagreeable fluids. These some discharge from the mouth; others from the anus; others again from the joints of the limbs and segments of the body; and a few from appropriate organs.
You have doubtless often observed a black beetle crossing pathways with a slow pace, which feeds upon the different species of bedstraw (Galium), called by some the bloody-nose beetle (Timarcha tenebricosa). This insect, when taken, usually ejects from its mouth a clear drop or two of red fluid, which will stain paper of an orange colour. The carrion-beetles (Silpha and Necrophorus), as also the larger Carabi, defile us, if handled roughly, with brown fetid saliva. Mr. Sheppard having taken one of the latter (C. violaceus), applied it in joke to his son's face, and was surprised to hear him immediately cry out as if hurt: repeating the experiment with another of his boys, he complained of its making him smart: upon this he touched himself with it, and it caused as much pain as if, after shaving, he had rubbed his face with spirits of wine. This he observed was not invariably the case with this beetle, its saliva at other times being harmless. Hence he conjectures that its caustic nature, in the instance here recorded, might arise from its food; which he had reason to think had at that time been the electric centipede (Geophilus electricus).—Lesser having once touched the anal horn of the caterpillar of some sphinx, suddenly turning its head round it vomited upon his hand a quantity of green viscous and very fetid fluid, which, though he washed it frequently with soap and fumed it with sulphur, infected it for two days[352].—Lister relates that he saw a spider, when upon being provoked it attempted to bite, emit several times small drops of very clear fluid[353].—Mr. Briggs observed a caterpillar caught in the web of one of our largest spiders, by means of a fluid which it sent forth entirely dissolve the great breadth of threads with which the latter endeavoured to envelop it, as fast as produced, till the spider appeared quite exhausted[354].—The caterpillars also of a particular tribe of saw-flies, remarkable for the beautiful pennated antennæ of the males (Pteronus)[355], when disturbed eject a drop of fluid from their mouth. Those of one species inhabiting the fir-tree (Pt. Pini) are ordinarily stationed on the narrow leaves of that tree—which they devour most voraciously in the manner that we eat radishes—with their head towards the point. Sometimes two are engaged opposite to each other on the same leaf. They collect in groups often of more than a hundred, and keep as close to each other as they can. When a branch is stripped they all move together to another. If one of these caterpillars be touched or disturbed, it immediately with a twist lifts the anterior part of its body, and emits from its mouth a drop of clear resin, perfectly similar both in odour and consistence to that of the fir[356]. What is still more remarkable, no sooner does a single individual of the group give itself this motion, than all the rest, as if they were moved by a spring, instantaneously do the same[357]. Thus these animals fire a volley as it were at their annoyers, the scent of which is probably sufficient to discomfit any ichneumons, flies, or predaceous beetles that may be desirous of attacking them.