Amongst those which annoy their enemies by the emission of fluids from their anus are the larger Carabi. These, if roughly handled, will spirt to a considerable distance an acrid, caustic, stinking liquor, which if it touch the eyes or the lips occasions considerable pain[358].—The rose-scented capricorn (Cerambyx moschatus) produced a similar effect upon Mr. Sheppard by similar means. The fluid in this had a powerful odour of musk.—The acid of ants has long been celebrated, and is one of their most powerful means of defence. When the species that have no sting make a wound with their jaws, they insinuate into it some of this acid, the effluvia produced by which are so subtile and penetrating, that it is impossible to hold your head near the nest of the hill-ant (Formica rufa), when the ants are much disturbed, without being almost suffocated. This odour thus proceeding from myriads of ants, is powerful enough, it is said, to kill a frog, and is probably the means of securing the nest from the attack of many enemies.—Dr. Arnold observed a species of bug (Scutellera) abundant upon some polygamous plant which he could not determine, and in all their different states. They were attended closely by hosts of ants, and when disturbed emitted a very strong smell. One of these insects ejected a minute drop of fluid into one of his eyes, which occasioned for some hours considerable pain and inflammation. In the evening, however, they appeared to subside;—but on the following morning the inflammation was renewed, became worse than ever, and lasted for three days.
Other insects, when under alarm, discharge a fluid from the joints and segments of their body. You have often seen what has been called the unctuous or oil beetle (Meloe Proscarabæus), and I dare say, when you took it, have observed orange-coloured or deep-yellow drops appear at its joints. As these insects feed upon acrid plants, the species of crowfoot or Ranunculus, it is probable that this fluid partakes of the nature of their food and is very acrimonious—and thus may put to flight its insect assailants or the birds, from neither of which it could otherwise escape, being a very slow and sluggish and at the same time very conspicuous animal. Another beetle (Ellenophorus collaris) has likewise this faculty.—The lady-bird, we know, has been recommended as a cure for the tooth-ache. This idea may have taken its rise from a secretion of this kind being noticed upon it. I have observed that one species (Coccinella bipunctata) when taken ejects from its joints a yellow fluid which yields a powerful but not agreeable scent of opium.—Asilus crabroniformis, a dipterous insect, once when I took it, emitted a white milky fluid from its proboscis, the joints of the legs and abdomen, and the anus.—The common scorpion-fly, likewise, upon the same occasion ejects from its proboscis a brown and fetid drop[359]. Some insects have peculiar organs from which their fluids issue, or are ejaculated. Thus the larvæ of saw-flies when taken into the hand cover themselves with drops, exuding from all parts of their body, of an unpleasant penetrating scent[360]. That of Cimbex lutea, of the same tribe, from a small hole just above each spiracle, syringes a similar fluid in horizontal jets of the diameter of a thread, sometimes to the distance of more than a foot[361].—The caterpillar of the great emperor moth (Saturnia Pyri,) also spirts out, when the spines that cover them are touched, clear lymph from its pierced tubercles[362].—Willughby has remarked a curious circumstance with respect to a water-beetle (Acilius sulcatus), which ought not to be overlooked. A transverse line of a pale colour is observable upon the elytra of the male; where this line terminates certain oblong pores are visible, from which he affirms he has often seen a milky fluid exuding[363]; and what may confirm his statement, I have more than once observed such a fluid issue from the male of this genus.—The caterpillar of the puss-moth (Cerura vinula), as well as those of several other species, has a cleft in the neck between the head and the first pair of legs. From this issues, at the will of the animal, a singular syringe, laterally bifid; the branches of which are terminated by a nipple perforated like the rose of a watering-pot. By means of this organ, when touched, it will syringe a fluid to a considerable distance, which, if it enters the eyes, gives them acute but not lasting pain. The animal when taken from the tree on which it feeds, though supplied with its leaves, loses this faculty, with which it is probably endowed to drive off the ichneumons that infest it[364].—And, to name no more, the great tiger-moth (Euprepia Caja), when in its last or perfect state, has near its head a remarkable tuft of the most brilliant carmine, from amongst the hairs of which, if the thorax be touched, some minute drops of transparent water issue, doubtless for some similar purpose[365].
The next active means of defence with which Creative Wisdom has endowed these busy tribes, are those limbs or weapons with which they are furnished. The insect lately mentioned, the puss-moth, besides the syringes just described, is remarkable for its singular forked tail, entirely dissimilar to the anal termination of the abdomen of most other caterpillars. This tail is composed of two long cylindrical tubes moveable at their base, and beset with a great number of short stiff spines. When the animal walks, the two branches of the tail are separated from each other, and at every step are lowered so as to touch the plane of position; hence we may conclude that they assist it in this motion and supply the place of hind legs. If you touch or otherwise incommode it, from each of the above branches there issues a long, cylindrical, slender, fleshy, and very flexible organ of a rose colour, to which the caterpillar can give every imaginable curve or inflection, causing it sometimes to assume even a spiral form. It enters the tube, or issues from it, in the same manner as the horns of snails or slugs. These tails form a kind of double whip, the tubes representing the handle, and the horns the thong or lash with which the animal drives away the ichneumons and flies that attempt to settle upon it. Touch any part of the body, and immediately one or both the horns will appear and be extended; and the animal will, as it were, lash the spot where it feels that you incommode it. De Geer, from whom this account is taken, says that this caterpillar will bite very sharply[366].—Several larvæ of butterflies, distinguished at their head by a semicoronet of strong spines, figured by Madame Merian, are armed with singular anal organs[367], which may have a similar use. Rösel when he first saw the caterpillar of the puss-moth, stretched out his hand with great eagerness, so he tells us, to take the prize; but when in addition to its grim attitude he beheld it dart forth these menacing catapults, apprehending they might be poisonous organs, his courage failed him. At length, without touching the monster, he ventured to cut off the twig on which it was, and let it drop into a box[368]! The caterpillar of the gold-tail moth (Arctia chrysorhœa) has a remarkable aperture, which it can open and shut, surrounded by a rim on the upper part of each segment. This aperture includes a little cavity, from which it has the power of darting forth small flocks of a cottony matter that fills it[369]. This manœuvre is probably connected with our present subject, and employed to defend it from its enemies. It also ejects a fluid from its anus.
There is a moth in New Holland, the larva of which annoys its foes in a different way: from eight tubercles in its back it darts forth, when alarmed, as many bunches of little stings, by which it inflicts very painful and venomous wounds[370].
The caterpillar of the moth of the beech (Stauropus Fagi), called the lobster, is distinguished by the uncommon length of its anterior legs. Mr. Stephens, an acute entomologist, relates to me that he once saw this animal use them to rid itself of a mite that incommoded it. They are probably equally useful in delivering it from the ichneumon and its other insect enemies.—Dr. Arnold has made a curious observation (confirmed by Dr. Forsström with respect to others of the genus) on the use of the long processes or tails that distinguish the secondary wings of Thecla Iarbas. These processes, he remarks, resemble antennæ, and when the butterfly is sitting it keeps them in constant motion; so that at first sight it appears to have a head at each extremity; which deception is much increased by a spot resembling an eye at the base of the processes. These insects, perhaps, thus perplex or alarm their assailants.—Goedart pretended that the anal horn with which the caterpillars of so many hawk-moths (Sphingidæ) are armed, answers the end of a sting instilling a dangerous venom: but the observations of modern entomologists have proved that this is altogether fabulous, since the animal has not the power of moving them[371]. Their use is still unknown.
Whether the long and often threatening horns on the head, thorax, and even elytra, with which many insects are armed, are beneficial to them in the view under consideration, is very uncertain. They are frequently sexual distinctions, and have a reference probably rather to sexual purposes and the economy of the animal, than to any thing else. They may, however, in some instances deter enemies from attacking them, and therefore it was right not to omit them wholly, though I shall not further enlarge upon them.—Their mandibles or upper jaws, though principally intended for mastication,—and in the case of the Hymenoptera, as instruments for various economical and mechanical uses,—are often employed to annoy their enemies or assailants. I once suffered considerable pain from the bite of the common water-beetle (Dytiscus marginalis), as well as from that of the great rove-beetle (Goerius olens); but the most tremendous and effectual weapon with which insects are armed—though this, except in the case of the scorpion, is also a sexual instrument, and useful to the females in oviposition—is their sting. With this they keep not only the larger animals, but even man himself, in awe and at a distance. But on these I enlarged sufficiently in a former letter[372].
These weapons, fearful as they are, would be of but little use to insects if they had not courage to employ them: in this quality, however, they are by no means deficient; for, their diminutive size considered, they are, many of them, the most valiant animals in nature. The giant bulk of an elephant would not deter a hornet, a bee, or even an ant, from attacking it, if it was provoked. I once observed a small spider walking in my path. On putting my stick to it, it immediately turned round as if to defend itself. On the approach of my finger, it lifted itself up and stretched out its legs to meet it.—In Ray's Letters mention is made of a singular combat between a spider and a toad fought at Hetcorne near Sittinghurst[373] in Kent; but as the particulars and issue of this famous duel are not given, I can only mention the circumstance, and conjecture that the spider was victorious[374]! Terrible as is the dragon-fly to the insect world in general, putting to flight and devouring whole hosts of butterflies, may-flies, and others of its tribes, it instills no terror into the stout heart of the scorpion-fly (Panorpa communis), though much its inferior in size and strength. Lyonnet saw one attack a dragon-fly of ten times its own bigness, bring it to the ground, pierce it repeatedly with its proboscis; and had he not by his eagerness parted them, he doubts not it would have destroyed this tyrant of the insect creation[375].
When the death's-head-hawk-moth was introduced by Huber into a nest of humble-bees, they were not affected by it, like the hive-bees, but attacked it and drove it out of their nest, and in one instance their stings proved fatal to it[376].—A black ground-beetle devours the eggs of the mole cricket, or Gryllotalpa. To defend them, the female places herself at the entrance of the nest—which is a neatly smoothed and rounded chamber protected by labyrinths, ditches, and ramparts—and whenever the beetle attempts to seize its prey, she catches it and bites it asunder[377].
I know nothing more astonishing than the wonderful muscular strength of insects, which in proportion to their size exceeds that of any other class of animals, and is likewise to be reckoned amongst their means of defence. Take one of the common chafers or dung-beetles (Geotrupes stercorarius, or Copris lunaris), into your hand, and observe how he makes his way in spite of your utmost pressure; and read the accounts which authors have left us of the very great weights that a flea will easily move, as if a single man should draw a waggon with forty or fifty hundred weight of hay:—but upon this I shall touch hereafter, and therefore only hint at it now.
We are next to consider the modes of concealment to which insects have recourse in order to escape the observation of their enemies. One is by covering themselves with various substances. Of this description is a little water-beetle (Elophorus aquaticus), which is always found covered with mud, and so when feeding at the bottom of a pool or pond can scarcely be distinguished, by the predaceous aquatic insects, from the soil on which it rests. Another very minute insect of the same order (Limnius æneus) that is found in rivulets under stones and the like, sometimes conceals its elytra with a thick coating of sand, that becomes nearly as hard as stone. I never met with these animals so circumstanced but once; then, however, there were several which had thus defended themselves, and I can now show you a specimen.—A species of a minute coleopterous genus (Georyssus areniferus[378]), which lives in wet spots where the toad-rush (Juncus bufonius) grows, covers itself with sand; and another nearly related to it (Chætophorus cretiferus, K.) which frequents chalk, whitens itself all over with that substance. As this animal, when clean, is very black, were it not for this manœuvre, it would be too conspicuous upon its white territory to have any chance of escape from the birds and its other assailants.—No insect is more celebrated for rendering itself hideous by a coat of dirt than the Reduvius personatus, a kind of bug sometimes found in houses. When in its two preparatory states, every part of its body, even its legs and antennæ, is so covered with the dust of apartments, consisting of a mixture of particles of sand, fragments of wool or silk, and similar matters, that the animal at first would be taken for one of the ugliest spiders. This grotesque appearance is aided and increased by motions equally awkward and grotesque, upon which I shall enlarge hereafter. If you touch it with a hair-pencil or a feather, this clothing will soon be removed, and you may behold the creature unmasked, and in its proper form. It is an insect of prey; and amongst other victims will devour its more hateful congener the bed-bug[379]. Its slow movements, combined with its covering, seem to indicate that the object of these manœuvres is to conceal itself from observation, probably, both of its enemies and of its prey. It is therefore properly noticed under my present head.