Chapter XIX
Of Insects

We are not writing a system of natural history; therefore we have not attended to the classes into which the subjects of that science are distributed. What we had to observe concerning different species of animals, fell easily, for the most part, within the divisions which the course of our argument led us to adopt. There remain, however, some, remarks upon the insect tribe which could not properly be introduced under any of these heads; and which therefore we have collected into a chapter by themselves.

The structure, and the use of the parts of insects, are less understood than that of quadrupeds and birds, not only by reason of their minuteness, or the minuteness of their parts—for that minuteness we can, in some measure, follow with glasses—but also by reason of the remoteness of their manners and modes of life from those of larger animals. For instance, insects, under all their varieties of form, are endowed with antennae, which is the name given to those long feelers that rise from each side of the head: but to what common use or want of the insect kind a provision so universal is subservient, has not yet been ascertained; and it has not been ascertained, because it admits not of a clear, or very probable comparison with any organs which we possess ourselves, or with the organs of animals which resemble ourselves in their functions and faculties, or with which we are better acquainted than we are with insects. We want a ground of analogy. This difficulty stands in our way as to some particulars in the insect constitution which we might wish to be acquainted with. Nevertheless, there are many contrivances in the bodies of insects, neither dubious in their use, nor obscure in their structure, and most properly mechanical. These form parts of our argument.

I. The elytra, or scaly wings of the genus of scarabaeus or beetle, furnish an example of this kind. The true wing of the animal is a light, transparent membrane, finer than the finest gauze, and not unlike it. It is also, when expanded, in proportion to the size of the animal, very large. In order to protect this delicate structure, and perhaps, also, to preserve it in a due state of suppleness and humidity, a strong, hard case is given to it in the shape of the horny wing which we call the elytron. When the animal is at rest, the gauze wings lie folded up under this impenetrable shield. When the beetle prepares for flying, he raises the integument, and spreads out his thin membrane to the air.* And it cannot be observed without admiration, what a tissue of cordage, that is, of muscular tendons, must run in various and complicated, but determinate directions, along this fine surface, in order to enable the animal either to gather it up into a certain precise form, whenever it desires to place its wings under the shelter which nature has given to them, or to expand again their folds when wanted for action.

In some insects, the elytra cover the whole body; in others, half; in others, only a small part of it; but in all, they completely hide and cover the true winds. Also,

Many or most of the beetle species lodge in holes in the earth, environed by hard, rough substances, and have fre­quently to squeeze their way through narrow passages; in which situation, wings so tender, and so large, could scarcely have escaped injury, without both a firm covering to defend them, and the capacity of collecting themselves up under its protection.

II. Another contrivance, equally mechanical and equally clear, is the awl, or borer, fixed at the tails of various species of flies; and with which they pierce, in some cases, plants; in others, wood; in others, the skin and flesh of animals; in others, the coat of the chrysalis of insects of a different species from their own; and in others, even lime, mortar, and stone. I need not add, that having pierced the substance, they deposit their eggs in the hole. The descriptions which naturalists give of this organ are such as the following: It is a sharp­pointed instrument, which, in its inactive state, lies concealed in the extremity of the abdomen, and which the animal draws out at pleasure, for the purpose of making a puncture in the leaves, stem, or bark of the particular plant which is suited to the nourishment of its young. In a sheath, which divides and opens whenever the organ is used, there is inclosed a compact, solid, dentated stem, along which runs a gutter or groove, by which groove, after the penetration is effected, the egg, assisted in some cases by a peristaltic motion, passes to its destined lodgement.  In the oestrus or gad-fly, the wimble draws out like the pieces of a spy-glass: the last piece is armed with three hooks, and is able to bore through the hide of an ox. Can any thing more be necessary to display the mechanism, than to relate the fact?

III. The stings of insects, though for a different purpose, are, in their structure, not unlike the piercer. The sharpness to which the point in all of them is wrought; the temper and firmness of the substance of which it is composed; the strength of the muscles by which it is darted out, compared with the smallness and weakness of the insect, and with the soft and friable texture of the rest of the body, are properties of the sting to be noticed, and not a little to be admired. The sting of a bee will pierce through a goatskin glove. It penetrates the human flesh more readily than the finest point of a needle. The action of the sting affords an example of the union of chemistry and mechanism, such as, if it be not a proof of contrivance, nothing is. First, as to the chemistry, how highly concentrated must be the venom, which, in so small a quantity, can produce such powerful effects! And in the bee we may observe that this venom is made from honey, the only food of the insect, but the last material from which I should have expected that an exalted poison could, by any process or digestion whatsoever, have been prepared.

In the next place, with respect to the mechanism, the sting is not a simple, but a compound instrument. The visible sting,* though drawn to a point exquisitely sharp, is in strictness only a sheath, for, near to the extremity, may be perceived by the microscope two minute orifices, from which orifices, in the act of stinging, and, as it should seem, after the point of the main sting has buried itself in the flesh, are launched out two subtile rays, which may be called the true or proper stings, as being those through which the poison is infused into the puncture already made by the exterior sting. I have said that chemistry and mechanism are here united; by which observation I meant, that all this machinery would have been useless, telum imbelle, if a supply of poison, intense in proportion to the smallness of the drop, had not been furnished to it by the chemical elaboration which was carried on in the insect's body; and that, on the other hand, the poison, the result of this process, could not have attained its effect, or reached its enemy, if, when it was collected at the extremity of the abdomen, it had not found there a machinery fitted to conduct it to the situations in which it was to operate—namely, an awl to bore a hole, and a syringe to inject the fluid. Yet these attributes, though combined in their action are independent in their origin. The venom does not breed the sting; nor does the sting concoct the venom.

IV. The proboscis, with which many insects are endowed, comes next in order to be considered. It is a tube attached to the head of the animal. In the bee, it is composed of two pieces, connected by a joint; for, if it were constantly extended, it would be too much exposed to accidental injuries; therefore, in its indolent state, it is doubled up by means of the joint, and in that position lies secure under a scaly penthouse. In many species of the butterfly, the proboscis, when not in use, is coiled up like a watch-spring. In the same bee, the proboscis serves the office of the mouth, the insect having no other; and how much better adapted it is than a mouth would be, for the collecting of the proper nourishment of the animal, is sufficiently evident. The food of the bee is the nectar of flowers; a drop of syrup, lodged deep in the bottom of the corollae, in the recesses of the petals, or down the neck of a monopetalous glove. Into these cells the bee thrusts its long narrow pump, through the cavity of which it sucks up this precious fluid, inaccessible to every other approach. It is observable also, that the plant is not the worse for what the bee does to it. The harmless plunderer rifles the sweets, but leaves the flower uninjured. The ringlets of which the proboscis of the bee is composed, the muscles by which it is extended and contracted, form so many microscopical wonders. The agility also with which it is moved can hardly fail to excite admiration. But it is enough for our purpose to observe in general, the suitableness of the structure to the use, of the means to the end, and especially the wisdom by which nature has departed from its most general analogy—for animals being furnished with mouths are such—when the purpose could be better answered by the deviation.

In some insects, the proboscis, or tongue, or trunk is shut up in a sharp-pointed sheath; which sheath being of a much firmer texture than the proboscis itself, as well as sharpened at the point, pierces the substance which contains the food, and then opens within the wound, to allow the inclosed tube, through which the juice is extracted, to perform its office. Can any mechanism be plainer than this is, or surpass this?

V. The metamorphosis of insects from grubs into moths and flies, is an astonishing process. A hairy caterpillar is transformed into a butterfly. Observe the change. We have four beautiful wings where there were none before; a tubular proboscis in the place of a mouth with jaws and teeth; six long legs instead of fourteen feet. In another case we see a white, smooth, soft worm turned into a black, hard, crustaceous beetle with gauze wings. These, as I said, are astonishing processes, and must require, as it should seem, a proportionably artificial apparatus. The hypothesis which appears to me most probable is, that in the grub there exist at the same time three animals, one within another, all nourished by the same digestion, and by a communicating circulation, but in different stages of maturity. The latest discoveries made by naturalists seem to favor this supposition. The insect already equipped with wings, is descried under the membranes both of the worm and nymph. In some species, the proboscis, the antennae, the limbs, and wings of the fly, have been observed to be folded up within the body of the caterpillar, and with such nicety as to occupy a small space only under the two first wings. This being so, the outermost animal, which, besides its own proper character, serves as an integument to the other two, being the farthest advanced, dies, as we suppose, and drops off first. The second, the pupa or chrysalis, then offers itself to observation. This also, in its turn, dies; its dead and brittle husk falls to pieces, and makes way for the appearance of the fly or moth. Now if this be the case, or indeed whatever explication be adopted, we have a prospective contrivance of the most curious kind; we have organizations three deep, yet a vascular system which supplies nutrition, growth, and life, to all of them together.

VI. Almost all insects are oviparous. Nature keeps her butterflies, moths, and caterpillars locked up during the winter in their egg-state; and we have to admire the various devices to which, if we may so speak, the same nature has resorted for the security of the egg. Many insects inclose their eggs in a silken web; others cover them with a coat of hair torn from their own bodies; some glue them together, and others, like the moth of the silk-worm, glue them to the leaves upon which they are deposited, that they may not be shaken off by the wind, or washed away by rain. Some, again, make incisions into leaves, and hide an egg in each incision; while some envelope their eggs with a soft substance, which forms the first aliment of the young animal; and some, again, make a hole in the earth, and having stored it with a quantity of proper food, deposit their eggs in it. In all which we are to observe, that the expedient depends not so much upon the address of the animal, as upon the physical resources of his constitution.

The art also with which the young insect is coiled up in the egg presents, where it can be examined, a subject of great curiosity. The insect, furnished with all the members which it ought to have, is rolled up into a form which seems to contract it into the least possible space; by which contraction, notwithstanding the smallness of the egg, it has room enough in its apartment, and to spare. This folding of the limbs appears to me to indicate a special direction; for if it were merely the effect of compression, the collocation of the parts would be more various than it is. In the same species, I believe, it is always the same.

These observations belong to the whole insect tribe, or to a great part of them. Other observations are limited to fewer species, but not perhaps less important or satisfactory.

I. The organization in the abdomen of the silk-worm or spider, whereby these insects form their thread, is as incontestably mechanical as a wire-drawer's mill. In the body of the silk-worm are two bags, remarkable for their form, position, and use. They wind round the intestine; when drawn out they are ten inches in length, though the animal itself be only two. Within these bays is collected a glue; and communicating with the bags are two paps or outlets, perforated like a grater by a number of small holes. The glue or gum being passed through these minute apertures, forms hairs of almost imperceptible fineness; and these hairs, when joined, compose the silk which we wind off from the cone in which the silkworm has wrapped itself up: in the spider, the web is formed from this thread. In both cases, the extremity of the thread, by means of its adhesive quality, is first attached by the animal to some external hold; and the end being now fastened to a point, the insect, by turning round its body, or by receding from that point, draws out the thread through the holes above described, by an operation, as has been observed, exactly similar to the drawing of wire. The thread, like the wire, is formed by the hole through which it passes. In one respect there is a difference. The wire is the metal unaltered, except in figure. In the animal process, the nature of the substance is somewhat changed as well as the form; for as it exists within the insect, it is a soft, clammy gum or glue. The thread acquires, it is probable, its firmness and tenacity from the action of the air upon its surface in the moment of exposure; and a thread so fine is almost all surface. This property, however, of the paste is part of the contrivance.

The mechanism itself consists of the bags or reservoirs into which the glue is collected, and of the external holes communicating with these bags; and the action of the machine is seen in the forming of a thread, as wire is formed, by forcing the material already prepared through holes of proper dimensions. The secretion is an act too subtile for our discernment, except as we perceive it by the produce. But one thing answers to another—the secretary glands to the quality and consistence required in the secreted substance, the bag to its reception. The outlets and orifices are constructed not merely for relieving the reservoirs of their burden, but for manufacturing the contents into a form and texture of great external use, or rather, indeed, of future necessity to the life and functions of the insect.

II. Bees, under one character or other, have furnished every naturalist with a set of observations. I shall in this place confine myself to one, and that is the relation which obtains between the wax and the honey. No person who has inspected a beehive can forbear remarking how commodiously the honey is bestowed in the comb, and among other advantages, how effectually the fermentation of the honey is prevented by distributing it into small cells. The fact is, that when the honey is separated from the comb and put into jars, it runs into fermentation with a much less degree of heat than what takes place in a hive. This may be reckoned a nicety; but independently of any nicety in the matter, I would ask, what could the bee do with the honey if it had not the wax; how, at least, could it store it up for winter? The wax, therefore, answers a purpose with respect to the honey, and the honey constitutes that purpose with respect to the wax. This is the relation be­tween them. But the two substances, though together of the greatest use, and without each other of little, come from a different origin. The bee finds the honey, but makes the wax. The honey is lodged in the nectaria of flowers, and probably undergoes little alteration—is merely collected; whereas the wax is a ductile, tenacious paste, made out of a dry powder, not simply by kneading it with a liquid, but by a digestive process in the body of the bee. What account can be rendered of facts so circumstanced, but that the animal being intended to feed upon honey, was by a peculiar external configuration enabled to procure it? That, moreover, wanting the honey when it could not be procured at all, it was farther endued with the no less necessary faculty of constructing repositories for its preservation? Which faculty, it is evident, must depend primarily upon the capacity of providing suitable materials. Two distinct functions go to make up the ability. First, the power in the bee, with respect to wax, of loading the farina of flowers upon its thighs. Microscopic observers speak of the spoon-shaped appendages with which the thighs of bees are beset for this very purpose; but inasmuch as the art and will of the bee may be supposed to be concerned in this operation, there is, secondly, that which does not rest in art or will—a digestive faculty, which converts the loose powder into a stiff substance. This is a just account of the honey and the honey­comb; and this account, through every part, carries a creative intelligence along with it.

The sting also of the bee has this relation to the honey, that it is necessary for the protection of a treasure which invites so many robbers.

III. Our business is with mechanism. In the panorpa tribe of insects, there is a forceps in the tail of the male insect, with which he catches and holds the female. Are a pair of pincers more mechanical than this provision in its structure; or is any structure more clear and certain in its design?

IV. St. Pierre tells us,* that in a fly with six feet—I do not remember that he describes the species—the pair next the head and the pair next the tail have brushes at their extremities, with which the fly dresses, as there may be occasion, the anterior or the posterior part of its body; but that the middle pair have no such brushes, the situation of these legs not admitting of the brushes, if they were there, being converted to the same use. This is a very exact mechanical distinction.

V. If the reader, looking to our distributions of science, wish to contemplate the chemistry as well as the mechanism of nature, the insect creation will afford him an example. I refer to the light in the tail of a glowworm. Two points seem to be agreed upon by naturalists concerning it: first, that it is phosphoric; secondly, that its use is to attract the male insect. The only thing to be inquired after is the singularity, if any such there be, in the natural history of this animal, which should render a provision of this kind more necessary for it than for other insects. That singularity seems to be the difference which subsists between the male and the female, which difference is greater than what we find in any other species of animal whatever. The glow­worm is a female caterpillar, the male of which is a fly, lively, comparatively small, dissimilar to the female in appearance, probably also as distinguished from her in habits, pursuits, and manners, as he is unlike in form and external constitution. Here then is the diversity of the case. The caterpillar cannot meet her companion in the air. The winged rover disdains the ground. They might never therefore be brought together, did not this radiant torch direct the volatile mate to his sedentary female.

In this example we also see the resources of art anticipated. One grand operation of chemistry is the making of phosphorus; and it was thought an ingenious device to make phosphoric matches supply the place of lighted tapers. Now this very thing is done in the body of the glowworm. The phosphorus is not only made, but kindled, and caused to emit a steady and genial beam, for the purpose which is here stated, and which I believe to be the true one.

VI. Nor is the last the only instance that entomology affords, in which our discoveries, or rather our projects, turn out to be imitations of nature. Some years ago a plan was suggested of producing propulsion by reaction in this way: by the force of a steam-engine, a stream of water was to be shot out of the stern of a boat, the impulse of which stream upon the water in the river was to push the boat itself forward; it is in truth the principle by which skyrockets ascend in the air. Of the use or practicability of the plan I am not speaking; nor is it my concern to praise its ingenuity; but it is certainly a contrivance. Now, if naturalists are to be believed, it is exactly the device which nature has made use of for the motion of some species of aquatic insects. The larva of the dragonfly, according to Adams, swims by ejecting water from its tail—is driven forward by the reaction of water in the pool upon the current issuing in a direction backward from its body.

VII. Again, Europe has lately been surprised by the elevation of bodies in the air by means of a balloon. The discovery consisted in finding out a manageable substance, which was, bulk for bulk, lighter than air; and the application of the discovery was to make a body composed of this substance bear up, along with its own weight, some heavier body which was attached to it. This expedient, so new to us, proves to be no other than what the Author of nature has employed in the gossamer spider. We frequently see this spider's thread floating in the air, and extended from hedge to hedge, across a road or brook of four or five yards width. The animal which forms the thread has no wings wherewith to fly from one extremity to the other of this line, nor muscles to enable it to spring or dart to so great a distance; yet its Creator has laid for it a path in the atmosphere, and after this manner. Though the animal itself be heavier than air, the thread which it spins from its bowels is specifically lighter. This is its balloon. The spider, left to itself, would drop to the ground; but being tied to its thread, both are supported. We have here a very peculiar provision; and to a contemplative eye it is a gratifying spectacle to see this insect wafted on her thread, sustained by a levity not her own, and traversing regions which, if we examined only the body of the animal, might seem to have been forbidden to its nature.

 

I must now crave the reader's permission to introduce into this place, for want of a better, an observation or two upon the tribe of animals, whether belonging to land or water, which are covered by shells.

I. The shells of snails are a wonderful, a mechanical, and, if one might so speak concerning the works of nature, an original contrivance. Other animals have their proper retreats, their hybernacula also, or winter-quarters, but the snail carries these about with him. He travels with his tent; and this tent, though, as was necessary, both light and thin, is completely impervious either to moisture or air. The young snail comes out of its egg with the shell upon its back; and the gradual enlargement which the shell receives, is derived from the slime excreted by the animal's skin. Now the aptness of this excretion to the purpose, its property of hardening into a shell, and the action, whatever it be, of the animal, whereby it avails itself of its gift, and of the constitution of its glands—to say nothing of the work being commenced before the animal is born—are things which can, with no probability, be referred to any other cause than to express design; and that not on the part of the animal alone—in which design, though it might build the house, it could not have supplied the material. The will of the animal could not determine the quality of the excretion. Add to which, that the shell of the snail, with its pillar and convolution, is a very artificial fabric; while a snail, as it should seem, is the most numb and unprovided of all artificers. In the midst of variety, there is likewise a regularity which could hardly be expected. In the same species of snail, the number of turns is usually, if not always, the same. The sealing up of the mouth of the shell by the snail, is also well calculated for its warmth and security; but the cerate is not of the same substance with the shell.

II. Much of what has been observed of snails belongs to shell-fish, and their shells, particularly to those of the univalve kind, with the addition of two remarks, one of which is upon the great strength and hardness of most of these shells. I do not know whether, the weight being given, art can produce so strong a case as are some of these shells; which defensive strength suits well with the life of an animal that has often to sustain the dangers of a stormy element and a rocky bottom, as well as the attacks of voracious fish. The other remark is upon the property, in the animal excre­tion, not only of congealing, but of congealing—or, as a builder would call it, setting—in water, and into a cretaceous substance, firm and hard. This property is much more extraordinary, and, chemically speaking, more specific, than that of hardening in the air, which may be reckoned a kind of exsiccation, like the drying of clay into bricks.

III. In the bivalve order of shell-fish, cockles, muscles, oysters, etc., what contrivance can be so simple or so clear as the insertion, at the back, of a tough tendinous substance, that becomes at once the ligament which binds the two shells together, and the hinge upon which they open and shut?

IV. The shell of a lobster's tail, in its articulations and overlappings, represents the jointed part of a coat of mail; or rather, which I believe to be the truth, a coat of mail is an mutation of a lobster's shell. The same end is to be answered by both; the same properties, therefore, are required in both, namely, hardness and flexibility—a covering which may guard the part without obstructing its motion. For this double purpose, the art of man, expressly exercised upon the subject, has not been able to devise any thing better than what nature presents to his observation. Is not this therefore mechanism, which the mechanics having a similar purpose in view, adopts? Is the structure of a coat of mail to be referred to art?  Is the same structure of the lobster, conducing to the same use, to be referred to any thing less than art?

Some who may acknowledge the imitation, and assent to the inference which we draw from it in the instance before us, may be disposed, possibly, to ask, why such imitations are not more frequent than they are, if it be true, as we allege, that the same principle of intelligence, design, and mechanical contrivance was exerted in the formation of natural bodies as we employ in the making of the various instruments by which our purposes are served? The answers to this question, are, first, that it seldom happens that precisely the same purpose, and no other, is pursued in any works which we compare of nature and of art; secondly, that it still more seldom happens that we can imitate nature, if we would. Our materials and our workmanship are equally deficient. Springs and wires, and cork and leather, produce a poor substitute for an arm or a hand. In the example which we have selected, I mean a lobster's shell compared with a coat of mail, these difficulties stand less in the way than in almost any other that call be assigned; and the consequence is, as we have seen, that art gladly borrows from nature her contrivance, and imitates it closely.

 

But to return to insects.  I think it is in this class of animals, above all others, especially when we take in the multitude of species which the microscope discovers, that we are struck with what Cicero has called "the insatiable variety of nature." There are said by St. Pierre to be six thousand species of flies; seven hundred and sixty butterflies; each different from all the rest. The same writer tells us, from his own observation, that thirty-seven species of winged insects, with distinctions well expressed, visited a single strawberry-plant in the course of three weeks.* Ray observed, within the compass of a mile or two of his own house, two hundred kinds of butterflies, nocturnal and diurnal. He likewise asserts, but I think without any grounds of exact computation, that the number of species of insects, reckoning all sorts of them, may not be short of ten thousand.† And in this vast variety of animal forms—for the observation is not confined to insects, though more applicable perhaps to them than to any other class—we are sometimes led to take notice of the different methods, or rather of the studiously diversified methods, by which one and the same purpose is attained. In the article of breathing, for example, which was to be provided for in some way or other, besides the ordinary varieties of lungs, gills, and breathing-holes—for insects in general respire, not by the mouth, but through holes in the sides—the nymphs of gnats have an apparatus to raise their backs to the top of the water, and so take breath. The hydrocanthari do the like by thrusting their tails out of the water.‡ The maggot of the eruca labra has a long tail, one part sheathed within another—but which it can draw out at pleasure—with a starry tuft at the end; by which tuft, when expanded upon the surface, the insect both supports itself in the water, and draws in the air which is necessary. In the article of natural clothing, we have the skins of animals invested with scales, hair, feathers, mucus, froth, or itself turned into a shell or crust.  In the no less necessary article of offence and defence, we have teeth, talons, beaks, horns, stings, prickles, with—the most singular expedient for the same purpose—the power of giving the electric shock, and, as is credibly related of some animals, of driving away their pursuers by an intolerable foetor, or of blackening the water through which they are pursued. The consideration of these appearances might induce us to believe that variety itself, distinct from every other reason, was a motive in the mind of the Creator, or with the agents of his will.

To this great variety in organized life the Deity has given, or perhaps there arises out of it, a corresponding variety of animal appetites. For the final cause of this we have not far to seek. Did all animals covet the same element, retreat, or food, it is evident how much fewer could be supplied and accommodated than what at present live conveniently together, and find a plentiful subsistence. What one nature rejects, another delights in. Food which is nauseous to one tribe of animals becomes, by that very property which makes it nauseous, an alluring dainty to another tribe. Carrion is a treat to dogs, ravens, vultures, fish. The exhalations of corrupted substances attract flies by crowds. Maggots revel in putrefaction.

* Vol. 1, p. 3

† Wisdom of God, p. 23

‡ Derham, p. 7