The Common Objects of the Country

Running in a straight line from head to tail is seen the digestive apparatus, consisting of throat, stomach, and intestines, with their modifications; and this apparatus is marked a a in the cut.

INTERIOR OF CATERPILLAR.

On the surface of the digestive apparatus, and straight along its centre, lies the nervous system, represented by tiny white threads dotted at regular distances by rather larger spots of the same substance. If the nerve is examined closely, it will be seen to be composed of two very slender threads, lying closely against each other, but easily separable: in which state they are shown. And the little knobs are called “ganglia,” each forming a nervous centre, from which smaller nerves radiate to the different portions of the body.

As for brains, the caterpillar dispenses with them almost entirely; and instead of wearing one large brain in the head, is furnished with a row of lesser brains, or ganglia, extending through its whole length. This is the reason why caterpillars are so tenacious of life. If a man loses his head, he dies immediately; but an insect is not nearly so fastidious, and continues to live for a long time without any head at all. Indeed, there are some insects, which, if beheaded, die, not so much on account of the head, but of the stomach: for, having then no mouth, they cannot eat, and so die of hunger. And some insects there are which positively live longer if decapitated than if left in possession of their head.

On the right hand may be seen a curiously twisted organ, marked c, swelling to a considerable size in the middle, and diminishing to a mere thread at each end. This is one of the vessels that contain the silk, or rather the substance which becomes silk when it is spun.

If this organ be cut open in the middle, it will be seen filled with a gummy substance of curious texture, partly brittle and partly tough. From this substance silk is spun, by passing up the tube, through the thread-like portion, and so at last into a tiny tube, called the spinneret, which opens from the mouth, and wherefrom it issues in a fine thread.

There are two of these silk-making organs, and both unite in the spinneret. Consequently, if silk is examined in the microscope, the double thread can clearly be made out, both threads adhering to each other, but still distinguishable. If the threads lie parallel to each other, the silk is good; if not so, it is of an inferior quality, and liable to snap.

Most caterpillars possess this silk-factory, but some have it much more largely developed than others—the silk-worm, for instance. It is of considerable size in the larva which we are examining, because the Woolly Bear has to spin for itself a silken hammock in which to swing while it is in the sleep of its pupal state. Just before it begins to spin, the organ is of very large size, and distended with the liquid silk; but after the hammock is completed, the organ diminishes to a mere thread, and is soon altogether absorbed.

At the left hand of the drawing may be seen a curious structure, marked b b. This is the chief portion of the respiratory system, and may be at once recognised by the ringed structure of the tube. Indeed it is quite analogous to that of the windpipe in animals.

The mode in which insects breathe differs much from that of the higher animals. In them the breathing apparatus is gathered into one mass, called lungs or gills, as the case may be; but with insects, the respiratory system runs entirely over, round, and through the body, even to the tips of the claws, and the end of the feelers or antennæ.

Every internal organ is also surrounded and enveloped by the breathing tubes; and this often to such an extent, that the dissector is sadly perplexed how to remove the tracheal tubes, as they are called, without injuring the organs to which they so tightly cling. Sometimes they are so strongly bound together, that they may be removed like a net, but mostly each must be taken away separately. The mode in which these tracheal tubes supply the digestive apparatus may be seen at b b; and as there is a double set of them, it may be seen how closely they envelop the organ to which they direct their course.

The ringed structure runs throughout the entire course of the air tubes, and is caused by a thread running spirally between the two membranes of which the tube is composed. The object of this curious thread is to keep the tube always distended, and ready for the passage of air. Otherwise, whenever the insect bends its flexible body, it would cut off the supply of air in every tube which partook of the flexure of the body.

The structure is precisely similar to that of a spiral wire bell-spring; and so strong is the thread, that I have succeeded in unwinding nearly two inches of it from the trachea of a humble bee.

The air obtains entrance into these tubes, not through the mouth or nostrils, but through a set of oval apertures arranged along the sides of the insect, which apertures are called “spiracles”; and two of them are indicated at b* b*.

In order to prevent dust, water, or anything but air, from entering, the spiracles are defended by an elaborate chevaux de frise of hair, or rather quill, so disposed as to keep out every particle that could injure. So powerful are these defences, that, even under the air-pump, I was unable to force a single particle of mercury through them, though a stick will be entirely permeated by the metal, so that if cut it starts from every pore. I kept the creature in a vacuum for three days, then plunged it under mercury, and let in the air. Even then no effect was produced, except that the whole of the stomach and intestinal canal were charged with mercury.

But, though the spiracles are such excellent defences against obnoxious substances, they are not capable of throwing off any substance that may choke them. Consequently, nothing is easier than to kill an insect humanely, if one only knows how; and few things more difficult, if one does not know.

For example, if ladies catch a wasp they proceed to immolate it by snipping it in two with their scissors; a dreadfully cruel process, for the poor creature has still some four or five brains left intact, and lives for many hours. But if a feather is dipped in oil and swept across the body of the creature, it collapses, turns on its back, and dies straightway. For the oil has stopped up the spiracles, and so the supply of air is cut off from every portion of the body at once. The same rule holds good with all insects.

There is yet one more organ to which I must draw attention, and that is the curious bag-shaped object marked e.

Just as the silk is contained in the vessel c, so the saliva is contained in e, and is developed according to the character and habits of the insect. Some insects require a large supply of that liquid, which is used for various purposes, and others require comparatively little. The caterpillar in which these receptacles may be found best developed is the larva of the Goat-moth, which may be easily found within the substance of decaying trees. Of the Goat-moth we may speak in a future page.

If the reader will again refer to the engraving on p. 100 (#x4_x_4_i150), he will see that between the tracheal tube and the digestive apparatus is a curiously waved line, forming two loops in its upper portion, and running into a confused entanglement below. This entanglement, however, is only apparent, for in nature there is no entangling; all is perfect in order.

This wavy line represents one of the numerous thread-like vessels that surround this portion of the digestive apparatus, and are called the biliary vessels, being, in fact, the insect’s liver. There is a large mass of these biliary vessels, and they are found so closely entwined among each other, and so encircled with the air tubes, that to separate them is no easy matter. Their microscopic structure is curious, and will repay a careful examination.

In examining the creature for the first time, the dissector will be tolerably sure to damage the organs and unfit it for preservation, and therefore it is best to take such a course for granted, and to make the best of it.

Removing all these vital organs, he should then examine the wonderful and most complicated muscular structure, by which the caterpillar is enabled to lengthen, shorten, twist, and bend its body in almost any direction, and that with such power that many caterpillars are enabled to stretch themselves horizontally into the air, and there to keep themselves motionless for hours together.

Few people have any idea of the wonders that they will find inside even so lowly a creature as a caterpillar—wonders, too, that only increase in number and beauty the more closely they are examined. When the outer form has been carefully made out, there yet remains the microscopical view, and after that the chemical, in either of which lie hidden innumerable treasures.

A very forcible and unsophisticated opinion was once expressed to me, after I had dissected and explained the anatomy of a silk-worm to an elderly friend. He remained silent for some time, and then uttered disconnected exclamations of astonishment.

I asked him what had so much astonished him.

“Why,” said he, “it’s that caterpillar. It is a new world to me. I always thought that caterpillars were nothing but skin and squash.”

Having now seen something of the exterior and interior of the caterpillar, we will watch it as it prepares for its next state of existence.

Hitherto it has been tolerably active, and if alarmed while feeding, it curls itself round like a hedgehog and falls to the ground, hoping to lie concealed among the foliage, and guarded from the effects of the fall by its hairy armour, which stands out on all sides, and secures it from harm. But a time approaches wherein it will have no defence and no means of escape, so it must find a means of lying quiet and concealed. This object it achieves in the following manner.

It leaves its food, and sets off on its travels to find a retired spot where it may sling its hammock and sleep in peace. Having found a convenient spot, it sets busily to work, and in a very short time spins for itself a kind of silken net, much like a sailor’s hammock in shape, and used in the same manner. It is not a very solid piece of work, for the creature can be seen through the meshes; but it is more than sufficiently strong to bear the weight of the inclosed insect, and to guard it from small foes.

On plate B (#x7_plateB), and fig. 5 b, the silken hammock is represented, the form of the pupa inside being visible. It casts off its skin for the last time, and instead of being a hirsute and active caterpillar, becomes a smooth and quiescent chrysalis. In this state it abides for a time that varies according to the time of year and the degree of temperature, and at last bursts its earthly holdings, coming to the light of the sun a perfect insect.

When first the creature becomes a chrysalis, its colour is white, and its surface is bathed in an oily kind of liquid, which soon hardens in the air, and darkens in the light.

On one occasion, I watched a Woolly Bear changing its skin, and, seizing it immediately that the task was accomplished, put it into spirits of wine, intending to keep it for observation.

Next day, the spirit was found to have dissolved away the oily coating, and all the limbs and wings of the future moth were standing boldly out.

Before closing this chapter, I must just remark that the absence of scientific terms throughout the work will be intentional, from a wish to make the subject intelligible, instead of imposing. It would have been easy enough to speak of the Woolly Bear as the larva of Arctia Caja; to describe it as a chilognathiform larva, with a subcylindrical body, and no thoracic shield: passing through an obtected metamorphosis, and becoming a pomeridian lepidopterous imago; and to have proceeded in the same style throughout. But as nearly every one who has taken a country walk has seen Woolly Bears, and hardly any one knows what is meant by “chilognathiform,” the subject is treated of for the benefit of the many, even at the risk of incurring the contempt of the few.

CHAPTER VI

THE PUSS-MOTH—CURIOUS CATERPILLAR—A STRONG FORTRESS—THE BURNET-MOTH—OAK EGGER—HOW TO KILL INSECTS—TWOFOLD LIFE—VICTIMS OF LOVE—ACUTE SENSES—THE STORY OF INSECT LIFE—DRINKER MOTH—CATERPILLAR BOX—EMPEROR MOTH—TYPE OF THE MOUSE-TRAP.

Just at the right hand of the Tiger-moth, on plate B (#x7_plateB), may be seen a caterpillar of a very strange and eccentric form, and marked by the number 4 a. This is the larva or caterpillar of the Puss-moth, and is no less beautiful in colouring than fantastic in form. Its attitude, too, when it is at rest, is quite as curious as its general appearance.

While eating, it sits on the leaves and twigs much as any other caterpillar; but when it ceases to feed, and reposes itself, it grasps the twig firmly with the claspers with which the hinder portion of its body is furnished, and raises the fore-part of its body half upright. In this attitude it much resembles that of the Egyptian Sphinx, and from this circumstance the moth itself is called a Sphinx. An old gardener was once quite put out of temper by seeing several of these caterpillars for the first time, because they had so consequential an air.

The colouring of this creature varies according to the time of year; but it may be easily recognised by its form alone, which is very peculiar.

One of the most remarkable points in the creature is the forked apparatus at the end of the tail, and which frightens people who do not know the habits of the caterpillar. These forks are black externally, and rather stiff, but are only sheaths for two curious rose-coloured tentacles, which are usually kept hidden, but which may be seen by touching the caterpillar with the point of a needle. When the creature is thus irritated, it will protrude these tentacles from their sheath, and will then strike the part that had been touched.

It is supposed that this apparatus is intended as a kind of whip, wherewith to drive away the ichneumon flies, and other parasites, that inflict such annoyance on many caterpillars.

When this caterpillar proceeds to its pupal state, it makes itself a wonderful fortress—not suspended like that of the Tiger-moth, nor hidden in a dark spot; but it boldly fixes its residence on the exterior of the tree on which it feeds, trusting to its similitude to the bark for concealment, and to the strength of its habitation for safety, even if discovered.

It is furnished with a gummy substance, something after the manner of the silk of the Tiger-moth; but instead of spinning that substance into threads, it uses it in the following manner.

Biting little chips of wood from the bark of the tree, the caterpillar glues them together with this natural cement; and so builds an arched house for itself, much about the size and shape of half a walnut-shell. So strongly compacted is this residence, that rain and wind have no effect on it, and a penknife does not find an easy entrance.

One or two of these caterpillars which I brought home modified their dwellings in a curious manner. One of them nibbled to pieces a portion of a cardboard box, and so made a kind of papier-maché house; while others, who were placed under a glass tumbler, and upon a stone surface, simply made their house of the hardened gum. In this state, it appeared as if it had been made of thin horn, and was so transparent that the chrysalis could be seen through the walls.

The caterpillar is common enough, and may be found on the willow or poplar. And a sharp eye will soon learn to detect the winter house, which to an unpractised eye looks as if it were merely a natural excrescence on the bark.

If one of these habitations is found, the best mode of removing it is to avoid touching the dwelling itself, but to cut away the bark round it; and then, by inserting the point of a stout knife, gently raise up the house, together with the bark on which it is placed. This is one of the modes by which an entomologist may find employment even during the winter months, and others will be mentioned in the course of this work.

The moth itself may be seen figured on plate B (#x7_plateB), fig. 4. It is called the Puss-moth, on account of the soft furry down with which its body is covered, and it is fancifully thought to resemble the fur of the cat.

It is rather a difficult moth to preserve effectually, as it is apt to become “greasy”—that is, to have its whole beauty destroyed by an oiliness that exudes from the body, and gradually creeps even over the wings. The best preservative is to remove the contents of the abdomen, and stuff it with cotton-wool that has been scented with spirits of turpentine. But even that plan is rather precarious, and the delicate, downy plumage is apt to be sadly damaged during the process of stuffing.