Chapter XI: Letter XXI (1)

_MEANS BY WHICH INSECTS DEFEND
THEMSELVES._

When a country is particularly open to attack, or surrounded by numerous enemies, who from cupidity or hostile feelings are disposed to annoy it, we are usually led to inquire what are its means of _defence?_ whether natural, or arising from the number, courage, or skill of its inhabitants. The insect tribes constitute such a nation: with them infinite hosts of enemies wage continual war, many of whom derive the whole of their subsistence from them: and amongst their own tribes there are numerous civil broils, the strong often preying upon the weak, and the cunning upon the simple: so that unless a watchful Providence (which cares for all its creatures, even the most insignificant,) had supplied them with some mode of resistance or escape, this innumerable race must soon be extirpated. That such is the case, it shall be my endeavour in this letter to prove; in which I shall detail to you some of the most remarkable means of defence with which they are provided. For the sake of distinctness I shall consider these under two separate heads, into which indeed they naturally divide themselves:--_Passive_ means of defence, such as are independent of any efforts of the insect; and _active_ means of defence, such as result from certain efforts of the insect in the employment of those instincts and instruments with which Providence has furnished it for this purpose.

I. The principal _passive_ means of defence with which insects are provided, are derived from their colour and form, by which they either deceive, dazzle, alarm, or annoy their enemies; or from their substance, involuntary secretions, vitality, and numbers.

They often _deceive_ them by imitating various substances. Sometimes they so exactly resemble the soil which they inhabit, that it must be a practised eye which can distinguish them from it. Thus, one of our scarcest British weevils (_Curculio nebulosus_), by its gray colour spotted with black, so closely imitates the soil consisting of white sand mixed with black earth, on which I have always found it, that its chance of escape, even though it be hunted for by the lyncean eye of an entomologist, is not small. Another insect of the same tribe (_Thylacites scabriculus_), of which I have observed several species of ground-beetles, (_Harpalus_, &c.) make great havoc, abounds in pits of a loamy soil of the same colour precisely with itself; a circumstance that doubtless occasions many to escape from their pitiless foes.--Several other weevils, for instance _Chlorima nivea_ and _cretacea_, resemble chalk, and perhaps inhabit a chalky or white soil.

Many insects also are like pebbles and stones, both rough and polished, and of various colours; but since this resemblance sometimes results from their attitudes, I shall enlarge upon it under my second head: whether, however, it be merely passive, or combined with action, we may safely regard it as given to enable them to elude the vigilance of their enemies.

A numerous host of our little animals escape from birds and other assailants by imitating the colour of the plants, or parts of them, which they inhabit; or the twigs of shrubs and trees; their foliage, flowers, and fruit. Many of the mottled moths, which take their station of diurnal repose on the north side of the trunks of trees, are with difficulty distinguished from the gray and green lichens that cover them. Of this kind are _Miselia aprilina_ and _Acronycta Psi_. The caterpillar of _Pœcilia? Algæ_, when it feeds on the yellow _Lichen juniperinus_, is always yellow; but when upon the gray _Lichen saxatilis_ its hue becomes gray[289]. This change is probably produced by the colour of its food. _Leptocerus atratus_, a kind of may-fly, frequents the black flower-spikes of the common sedge (_Carex riparia_), which fringes the banks of our rivers. I have often been unable to distinguish it from them, and the birds probably often make the same mistake and pass it by.--A jumping bug, very similar to one figured by Schellenberg[290], also much resembles the lichens of the oak on which I took it.

The Spectre tribe (_Phasma_) go still further in this mimicry, representing a small branch with its spray. I have one from Brazil eight inches long, that, unless it was seen to move, could scarcely be conceived to be any thing else; the legs as well as the head, having their little snags and knobs, so that no imitation can be more accurate. Perhaps this may be the species mentioned by Molina[291], which the natives of Chili call "The Devil's Horse[292]."

Other insects, of various tribes, represent the leaves of plants, living, decaying, and dead; some in their colour, and some both in their colour and shape. The caterpillar of a moth (_Hadena Ligustri_) that feeds upon the privet, is so exactly of the colour of the underside of the leaf, upon which it usually sits in the day-time, that you may have the leaf in your hand and yet not discover it[293].--The tribe of grasshoppers, called _Locustæ_ by Fabricius, though the true _Locust_ does not belong to it, in the veining, colour, and texture of their elytra, resemble green leaves[294].--The tribe of _Phasmina_--named praying-insects and spectres--also of the _Orthoptera_ order, often exhibit the same peculiarity.--Others of them, by the spots and mixtures of colour observable in these organs, represent leaves that are decaying in various degrees.--Those of several species of _Mantidæ_ likewise imitate dry leaves, and so exactly, by their opacity, colour, rigidity, and veins, that, were no other part of the animal visible, even after a close examination, it would be generally affirmed to be nothing but a dry leaf. Of this nature is the _Phyllium siccifolium_, and two or three Brazilian species in my cabinet, that seem undescribed, which I will show you when you give me an opportunity. But these imitations of dry leaves are not confined to the _Orthoptera_ order solely. Amongst the _Hemiptera_, the _Acanthia paradoxa_, a kind of bug, surprised Sparrman not a little. He was sheltering himself from the mid-day sun, when the air was so still and calm as scarcely to shake an aspen leaf, and saw with wonder what he mistook for a little withered, pale, crumpled leaf, eaten as it were by caterpillars, fluttering from the tree. The sight appeared to him so very extraordinary, that he left his place of shelter to contemplate it more nearly; and could scarcely believe his eyes, when he beheld a living insect, in shape and colour resembling a fragment of a withered leaf with the edges turned up and eaten away as it were by caterpillars, and at the same time all over beset with prickles[295].--A British insect, one of our largest moths (_Gastropacha quercifolia_), called by collectors the _Lappet-moth_, affords an example from the _Lepidoptera_ order of the imitation in question, its wings representing, both in shape and colour, an arid brown leaf. Some bugs, belonging to the genus _Dictyonota_ of Mr. Curtis[296], simulate portions of leaves in a still further state of decay, when the veins only are left. For, the thorax and elytra of these insects being reticulated, with the little areas or meshes of the net-work transparent, this circumstance gives them exactly the appearance of small fragments of skeletons of leaves.

But you have probably heard of most of these species of imitation: I hope, therefore, you will give credit to the two instances to which I shall next call your attention, of insects that even mimic flowers and fruit. With respect to the former, I recollect to have seen in a collection made by Mr. Masson at the Cape of Good Hope, a species of the orthopterous genus _Pneumora_, the elytra of which were of a rose- or pink-colour, which shrowding its vesiculose abdomen, gave it much the appearance of a fine flower--A most beautiful and brilliant beetle, of the genus _Chlamys_, (_Ch. Bacca_,) found by Captain Hancock in Brazil, by the inequalities of its ruby-coloured surface, strikingly resembles some kinds of fruit.--And to make the series of imitations complete, a minute black beetle, with ridges upon its elytra, (_Onthophilus sulcatus_[297],) when lying without motion, is very like the seed of an umbelliferous plant. The dog-tick is not unlike a small bean; which resemblance has caused a bean, commonly cultivated as food for horses, to be called the _tick-bean_. The Palma Christi, also, had probably the name of _Ricinus_ given to it from the similitude of its seed to a tick.

Another tribe of these little animals, before alluded to, is secured from harm by a different kind of imitation, and affords a beautiful instance of the wisdom of Providence in adapting means to their end. Some singular larvæ, with a radiated anus[298], live in the nests of humble-bees, and are the offspring of a particular genus of flies, (_Volucella_,) many of the species of which strikingly resemble those bees in shape, clothing, and colour. Thus has the Author of nature provided that they may enter these nests and deposit their eggs undiscovered. Did these intruders venture themselves amongst the humble-bees in a less kindred form, their lives would probably pay the forfeit of their presumption. Mr. Sheppard once found one of these larvæ in the nest of _Bombus_[299] _Raiellus_, but we could not ascertain what the fly was. Perhaps it might be _Volucella bombylans_, which resembles those humble-bees that have a red anus[300].

The brilliant colours in which many insects are arrayed, may decorate them with some other view than that of mere ornament. They may _dazzle_ their enemies. The radiant blue of the upper surface of the wings of a giant butterfly, abundant in Brazil (_Morpho Menelaus_), which from its size would be a ready prey for any insectivorous birds, by its splendour (which I am told, when the insect is flying in the sunshine, is inconceivably bright,) may produce an effect upon the sight of such birds, that may give it no small chance of escape. Latreille has a similar conjecture with respect to the golden wasps (_Chrysis_, L.). These animals lay their eggs in the nests of such _Hymenoptera_, wasps, bee-wasps (_Bembex_), and bees,--as are redoubtable for their stings; and therefore have the utmost occasion for protection against these murderous weapons. Amongst other defences the golden wasps are adorned with the most brilliant colours, which by their radiance, especially in the sunny situations frequented by these insects, may dazzle the eyes of their enemies, and enable them to effect unhurt the purpose for which they were created[301].

The frightful aspect of certain insects is another passive mean of defence by which they sometimes strike beholders, especially children, often great insect tormentors, with _alarm_, and so escape. The terrific and protended jaws of the stag-beetle (_Lucanus Cervus_) in Europe, and of the stag-horn capricorn beetle (_Prionus cervicornis_) in America, may save them from the cruel fate of the poor cockchafer[302], whose gyrations and motions, when transfixed by a pin, too often form the amusement of ill-disciplined children. The threatening horns also, prominent eyes, or black and dismal hue of many other _Coleoptera_ belonging to Linné's genera _Scarabæus_, _Cicindela_, and _Carabus_, may produce the same effect.

But the most striking instances of armour are to be found amongst the homopterous _Hemiptera_. In some of these, the horns that rise from the thorax are so singular and monstrous, that nothing parallel to them can be found in nature. Of this kind is the _Cicada spinosa_, Stoll[303], the _Centrotus clavatus_[304], and more particularly the _Centrotus globularis_[305], so remarkable for the extraordinary apparatus of balls and spines, which it appears to carry erect, like a standard, over its head. What is the precise use of all the varieties of armour with which these little creatures are furnished it is not easy to say, but they may probably defend them from the attack of some enemies.

Under this head I may mention the long hairs, stiff bristles, sharp spines, and hard tubercular prominences with which many caterpillars are clothed, bristled, and studded. That these are means of defence is rendered more probable by the fact that, in several instances, the animals so distinguished, at their last moult, previous to their assuming the pupa, (in which state they are protected by other contrivances,) appear with a smooth skin, without any of the tubercles, hairs, or spines for which they were before remarkable[306]. Wonderful are the varieties of this kind which insects exhibit:--but upon these I shall treat more at large on a future occasion. I shall only here select a few facts more particularly connected with my present subject. The caterpillar of the great tiger-moth (_Euprepia Caja_), which is beset with long dense hairs, when rolled up--an attitude it usually assumes if alarmed--cannot then be taken without great difficulty, slipping repeatedly from the pressure of the fingers. If its hairs do not render it distasteful, this may often be the mean of its escape from the birds.--That little destructive beetle, _Anthrenus Musorum_, which so annoys the entomologist, if it gets into his cabinets, when in the larva state being covered with bunches of diverging hairs, glides from between your fingers as if it were lubricated with oil. The two tufts of hairs near the tail of this are most curious in their structure, being jointed through their whole length, and terminating in a sharp halberd-shaped point[307].--I have a small lepidopterous caterpillar from Brazil, the upper side of which is thickly beset with strong, sharp, branching spines, which would enter into the finger, and would probably render it a painful morsel to any minor enemy.

The powers of _annoyance_, by means of their hairs, with which the moth of the fir, and the procession-moth, before noticed[308], are gifted, are doubtless a defensive armour to them.--Madame Merian has figured an enormous caterpillar of this kind,--which unfortunately she could not trace to the perfect insect,--by the very touch of which her hands, she says, were inflamed, and that the inflammation was succeeded by the most excruciating pain[309]. The vesicatory beetles, likewise, (_Cantharis vesicatoria_, &c.) are not improbably defended from their assailants by the remarkable quality, so useful to suffering mortals, that distinguishes them.

Your own observation must have proved to you, that insects often escape great perils, from the crush of the foot, or of superincumbent weights, by the hardness of the _substance_ that covers great numbers of them. The elytra of many beetles of the genus _Hister_ are so nearly impenetrable, that it is very difficult to make a pin pass through them; and the smaller stag-beetle (_Dorcus parallelopipedus_) will bear almost any weight--the head and trunk forming a slight angle with the abdomen--which passes over it upon the ground. Other insects are protected by the toughness of their skin. A remarkable instance of this is afforded by the common forest-fly (_Hippobosca equina_), which, as was before observed[310], can scarcely be killed by the utmost pressure of the finger and thumb.

The _involuntary secretions_ of these little beings may also be regarded as means of defence, which either conceal them from their enemies, make them more difficult to be attacked, or render them less palatable. Thus, the white froth often observable upon rose-bushes, and other shrubs and plants, called by the vulgar frog-spittle,--but which, if examined, will be found to envelop the larva of a small hemipterous insect (_Cercopis spumaria_), from whose anus it exudes, although it is sometimes discovered even in this concealment by the indefatigable wasps, and becomes their prey,--serves to protect the insect, which soon dies when exposed, not only from the heat of the sun and from violent rains, but also to hide it from the birds and its other foes.--The cottony secretion that transpires through the skin of _Myzoxyla_[311], and some species of _Coccus_, and in which the eggs of the latter are often involved, may perhaps be of use to them in this view; either concealing them--for they look rather like little locks of cotton, or feathers, than any thing animated--or rendering them distasteful to creatures that would otherwise prey upon them.--The same remark may apply to the slimy caterpillars of some of the saw-flies (_Tenthredo Cerasi_, _Allantus Scrophulariæ_ &c.) The coat of slime of these animals, as Professor Peck observes[312], retains its humidity though exposed to the fiercest sun.--Under this head I shall also mention the phosphoric insects: the glow-worm (_Lampyris_); the lantern-fly (_Fulgora_); the fire-fly (_Elater_); and the electric centipede (_Geophilus electricus_); since the light emitted by these animals may defend them from the attack of some enemies. Mr. Sheppard once noticed a Carabus running round the last-mentioned insect, when shining, as if wishing but afraid to attack it.

Various insects, doubtless, find the wonderful _vitality_[313] with which they are endowed another mean of defence; at least of obviating the effects of an attack. So that, when to all appearance they are mortally wounded, they recover, and fulfil the end of their creation. Indeed female _Lepidoptera_, especially of the larger kinds, will scarcely die, do what you will, till they have laid their eggs.--Dr. Arnold, a most acute observer, relates to Mr. MacLeay, that having pinned _Scolia quadrimaculata_, a hymenopterous insect, down in the same box with many others, amongst which was the humming-bird hawk-moth (_Macroglossa stellatarum_), its proper food; it freed itself from the pin that transfixed it, and, neglecting all the other insects in the box, attacked the Sphinx, and pulling it to pieces devoured a large portion of its abdomen.

We often wonder how the cheese-mite (_Acarus Siro_) is at hand to attack a cheese wherever deposited; but when we learn from Leeuwenhoek, that one lived eleven weeks gummed on its back to the point of a needle without food, our wonder will be diminished[314]. Another species of mite (_Uropoda vegetans_) was observed by De Geer to live some time in spirits of wine[315]. This last circumstance reminds me of an event which befel myself, that I cannot refrain from relating to you, since it was the cause of my taking up the pursuit I am recommending to you. One morning I observed on my study window a little lady-bird yellow with black dots (_Coccinella_ 22-_punctata_)--"You are very pretty," said I to myself, "and I should like to have a collection of such creatures." Immediately I seized my prey, and not knowing how to destroy it, I immersed it in geneva. After leaving it in this situation a day and a night, and seeing it without motion, I concluded it was dead, and laid it in the sun to dry. It no sooner, however, felt the warmth than it began to move, and afterward flew away. From this time I began to attend to insects.--The chamæleon-fly (_Stratyomis Chamæleon_) was observed by Swammerdam to retain its vital powers after an immersion equally long in spirits of wine. Gœdart affirms that this fly, on which account it was called chamæleon, will live nine months without food; a circumstance, if true, more wonderful than what I formerly related to you with respect to one of the aphidivorous flies[316].--If insects will escape unhurt from a bath of alcohol, it may be supposed that one of water will be less to be dreaded by them. To this they are often exposed in rainy weather, when ruts and hollows are filled with water: but when the water is dried up, it is seldom that any dead carcases of insects are to be seen in them. Mr. Curtis submerged the fragile aphides for sixteen hours; when taken out of the water they immediately showed signs of life, and out of four, three survived the experiment:--an immersion of twenty-four hours, however, proved fatal to them[317].

The late ingenious, learned, and lamented Dr. Reeve of Norwich once related to me that he found in a hot fountain on the top of a mountain, near Leuk in the Valais in Switzerland, in which the thermometer stood at 205°, transparent larvæ, probably of gnats, or some such insect.--Lord Bute also, in a letter to my late revered friend, the Rev. William Jones of Nayland, imparts a similar observation made by His Lordship at the baths of Abano, near the Euganian mountains, on the borders of the Paduan states. They are strong, sulphureous, boiling springs, oozing out of a rocky eminence in great numbers, and spreading over an acre of the top of a gentle hill. In the midst of these boiling springs, within three feet of five or six of them, rises a tepid one about blood warm. But the most extraordinary circumstance which he relates is, that not only confervas were found in the _boiling_ springs, but numbers of small black beetles, that died upon being taken out and plunged into cold water[318].--And once, having taken in the hot dung of my cucumber-bed a small beetle (_Synchita Juglandis_), I immersed it in boiling water; and after keeping it submerged a sufficient time, as I thought, to destroy it, upon taking it out, and laying it to dry, it soon began to move and walk. Its native station being of so high a temperature, Providence has fitted it for it, by giving it extraordinary powers of sustaining heat. Other insects are as remarkable for bearing any degree of cold. Some gnats that De Geer observed, survived after the water in which they were was frozen into a mass of ice: and Reaumur relates many similar instances[319].

The last passive means of defence that I mentioned, was the _multiplication_ of insects. Some species, the Aphides for instance, and the Grasshoppers and Locusts, have such an infinite host of enemies, that were it not for their numbers the race would soon be annihilated.--But as passive means of defence have detained us sufficiently long, it is enough to have touched upon this head. Let us then now proceed to such as may be called active; in which the volition of the animal bears some part.

II. The _active_ means of defence, which tend to secure insects from injury or attack, are much more numerous and diversified than the passive; and also more interesting, since they depend, more or less, upon the efforts and industry of these creatures themselves. When urged by danger, they endeavour to repel it either by having recourse to certain attitudes or motions; producing particular noises; emitting disagreeable scents or fluids; employing their limbs; or weapons, and valour; concealing themselves in various ways; or by counteracting the designs and attack of their enemies by contrivances that require ingenuity and skill.

The _attitudes_ which insects assume for this purpose are various. Some are purely imitative, as in many instances detailed above. I possess a diminutive rove-beetle (_Aleochara complicans_, K. Ms.) to which my attention was attracted as a very minute, shining, round, black pebble. This successful imitation was produced by folding its head under its breast, and turning up its abdomen over its elytra; so that the most piercing and discriminating eye would never have discovered it to be an insect.--I have observed that a carrion beetle (_Silpha thoracica_) when alarmed has recourse to a similar manœuvre. Its orange-coloured thorax, the rest of the body being black, renders it particularly conspicuous. To obviate this inconvenience, it turns its head and tail inwards till they are parallel with the trunk and abdomen, and gives its thorax a vertical direction, when it resembles a rough stone.--The species of another genus of beetles (_Agathidium_) will also bend both head and thorax under the elytra, and so assume the appearance of shining globular pebbles.

Related to the defensive attitude of the two last-mentioned insects, and precisely the same with that of the Armadillo (_Dasypus_) amongst quadrupeds, is that of one of the species of woodlouse (_Armadillo vulgaris_). This insect when alarmed rolls itself up into a little ball. In this attitude its legs and the underside of the body, which are soft, are entirely covered and defended by the hard crust that forms the upper surface of the animal. These balls are perfectly spherical, black, and shining, and belted with narrow white bands, so as to resemble beautiful beads; and could they be preserved in this form and strung, would make very ornamental necklaces and bracelets. At least so thought Swammerdam's maid, who, finding a number of these insects thus rolled up in her master's garden, mistaking them for beads, employed herself in stringing them on a thread; when to her great surprise, the poor animals beginning to move and struggle for their liberty, crying out and running away in the utmost alarm she threw down her prize[320].--The golden-wasp tribe also, (_Chrysis_ and _Parnopes_,) all of which I suspect to be parasitic insects, roll themselves up, as I have often observed, into a little ball when alarmed, and can thus secure themselves--the upper surface of the body being remarkably hard, and impenetrable to their weapons--from the stings of those _Hymenoptera_ whose nests they enter with the view of depositing their eggs in their offspring. Latreille noticed this attitude in _Parnopes carnea_, which, he tells us, _Bembex rostrata_ pursues, though it attacks no other similar insect, with great fury; and, seizing it with its feet, attempts to dispatch it with its sting, from which it thus secures itself[321].

Other insects endeavour to protect themselves from danger by simulating death. The common dung-chafer (_Geotrupes stercorarius_) when touched, or in fear, sets out its legs as stiff as if they were made of iron-wire--which is their posture when dead--and remaining perfectly motionless, thus deceives the rooks which prey upon them, and like the ant-lion before celebrated[322] will eat them only when alive. A different attitude is assumed by one of the tree-chafers (_Hoplia pulverulenta_) probably with the same view. It sometimes elevates its posterior legs into the air, so as to form a straight vertical line, at right angles with the upper surface of its body.--Another genus of insects of the same order, the pill-beetles (_Byrrhus_), have recourse to a method the reverse of this. They pack their legs, which are short and flat, so close to their body, and lie so entirely without motion when alarmed, that they look like a dead body, or rather the dung of some small animal.--Amongst the weevil tribe, most of the species of Germar's genus _Cryptorynchus_, including several modern genera or subgenera, when an entomological finger approaches them, as I have often experienced to my great disappointment, applying their rostrum and legs to the underside of their trunk, fall from the station on which you hope to entrap them, to the ground or amongst the grass; where, lying without stirring a limb, they are scarcely to be distinguished from the soil around them. Thus also, doubtless, they often disappoint the birds as well as the entomologist.--A little timber-boring beetle (_Anobium pertinax_), (and others of the genus have the same faculty,) which, when the head is withdrawn somewhat within the thorax, much resembles a monk with his hood, has long been famous for a most pertinacious simulation of death. All that has been related of the heroic constancy of American savages, when taken and tortured by their enemies, scarcely comes up to that which these little creatures exhibit. You may maim them, pull them limb from limb, roast them alive over a slow-fire[323], but you will not gain your end; not a joint will they move, nor show by the least symptom that they suffer pain. Do not think, however, that I ever tried these experiments upon them myself, or that I recommend you to do the same. I am content to believe the facts that I have here stated upon the concurrent testimony of respectable witnesses, without feeling any temptation to put the constancy of the poor insect again to the test.--A similar apathy is shown by some species of saw-flies (_Serrifera_), which when alarmed conceal their antennæ under their body, place their legs close to it, and remain without motion even when transfixed by a pin.--Spiders also simulate death by folding up their legs, falling from their station, and remaining motionless; and when in this situation, they may be pierced and torn to pieces without their exhibiting the slightest symptom of pain[324].

There is a certain tribe of caterpillars called surveyors (_Geometræ_), that will sometimes support themselves for whole hours, by means of their posterior legs, solely upon their anal extremity, forming an angle of various degrees with the branch on which they are standing, and looking like one of its twigs. Many concurring circumstances promote this deception. The body is kept stiff and immoveable with the separations of the segments scarcely visible; it terminates in a knob, the legs being applied close, so as to resemble the gem at the end of a twig; besides which, it often exhibits intermediate tubercles which increase the resemblance. Its colour too is usually obscure, and similar to that of the bark of a tree. So that, doubtless, the sparrows and other birds are frequently deceived by this manœuvre, and thus balked of their prey. Rösel's gardener, mistaking one of these caterpillars for a dead twig, started back in great alarm when upon attempting to break it off he found it was a living animal[325].

But insects do not always confine themselves to attitudes by which they meditate escape or concealment; they sometimes, to show their courage, put themselves in a posture of defence, and even have in view the annoyance as well as the repelling of their foes. The great rove-beetle (_Goerius olens_) presents an object sufficiently terrific, when with its large jaws expanded, and its abdomen turned over its head, like a scorpion, it menaces its enemies, some of which this ferocious attitude may deter from attacking it. Mr. Bingley informs us that the giant earwig (_Labidura gigantea_), a rare species that his researches have added to the catalogue of British insects, turns up over its head, in a similar manner, its abdomen, which being armed at the end with a large forceps must give it an appearance still more alarming[326].

The caterpillars of some hawk-moths (_Sphinx_), particularly that which feeds upon the privet, when they repose, holding strongly with their prolegs the branch on which they are standing, rear the anterior part of their body so as to form nearly a right angle with the posterior; and in this position it will remain perfectly tranquil,--thus eluding the notice of its enemies, or alarming them,--perhaps for hours. Reaumur relates that a gardener in the employment of the celebrated Jussieu used to be quite disconcerted by the self-sufficient air of these animals, saying they must be very proud, for he had never seen any other caterpillars hold their head so high[327]. From this attitude, which precisely resembles that which sculptors have assigned to the fabulous monster called by that name, the term _Sphinx_ has been used to designate this genus of insects.--The caterpillar of a moth (_Lophopteryx camelina_) noticed by the author just quoted, whenever it rests from feeding, turns its head over its back, then become concave, at the same time elevating its tail, the extremity of which remains in a horizontal position, with two short horns like ears behind it. Thus the six anterior legs are in the air, and the whole animal looks like a quadruped in miniature; the tail being its head--the horns its ears--and the reflexed head simulating a tail curled over its back[328]. In this seemingly unnatural attitude it will remain without motion for a very long time.

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.

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.