CHAPTER II.

WHAT IS A PUPA?

But it may now be asked, What is a pupa, and what are the differences between it and a larva, and between it and the perfect insect? It is very necessary that this should be clearly understood; and to that end we shall endeavour to render our explanation as simple as possible. But it will be far better than the best description, if the reader will be persuaded to watch these changes throughout himself. The butterfly tribe furnish the very best illustrations in the world; and by merely collecting a few caterpillars from the way-side, or from the kitchen-garden, a source of amusement will be opened which will a thousand-fold repay the trouble and time consumed in the occupation. Of all other ways, personal observation, when it is so readily to be effected as in the case of these insects, is the best and most impressive method of becoming acquainted with the "Life of an Insect." Such knowledge is far more entertaining than book-knowledge, and is much more agreeable to acquire, and more easy to retain.

We must guard our definition of what a pupa is, by reminding the reader that some insects with which he is very familiar do not pass through this change in the same manner that the majority of insects do; that is, in a state of torpor or sleep. If he were to rear up a spider from the egg, and were to watch for the time when it would become a still, lifeless-looking object, like that which we have called a pupa, he would assuredly be disappointed, and he might accuse this little work of leading him into error, because it declares that all insects must pass through the pupa state before they become perfect in their form and number of their parts. Yet that very spider has passed through both the larva and the pupa state under the observer's eye without his being able to recognise the fact, simply because in both these states it is very like the perfect insect, and can walk about and eat just as usual. In fact, it is more than probable that spiders of the same kind in these different conditions could scarcely be recognised so as to say that they were pupæ, or perfect insects, even by tolerable entomologists; and it is very likely that mistakes of this kind have often occurred.[I] We learn, therefore, from this statement, that some pupæ are active, and move about just as they did before, although they _are_ in the pupa state.

In a great number of cases, then, a pupa is a state in an insect's life when it rests from active exertion, and from taking food, and when, underneath the dry and withered skin, a series of great changes are taking place, which are preparing it for its future life in the perfect state. Thus it differs from the _larva_ state in not eating and moving, and in the important particular,--that it is receiving new parts and organs, which are added to it under the skin. It also differs from the _perfect insect_ in the same respects as in the first place from the larva, and also in the important circumstance, that the perfect insect the moment it enters that state, has no more organs added to it--it is, in fact, perfect, while the pupa is imperfect. Let us place these differences in a tabular form:--

The Larva The Pupa The Perfect Insect

Moves about and eats. Does not move about Moves about and eats. nor eat. Has no new organs Has no new organs added to it beyond Has several new organs added to it, beyond those acquired in the added to it, to prepare those obtained in egg. it for the perfect state. the pupa state.

Let us repeat our caution, that this definition is only applicable to _inactive_ pupæ. In the active pupæ the same development of new organs takes place, but it does not interfere with the usual actions of life. We must also add, that some of the pupæ which we must call inactive, nevertheless are not wholly without motion, but are capable of manifesting that life is in them, death-like though they appear, by slightly moving the lower part of the body.[J] All inactive pupæ, however, are without the power of moving about.

At the risk of being thought tedious, it has been indispensably necessary to be thus precise upon this point; a little careful study of these two or three pages will fix the distinctive characters of the pupa firmly in the reader's memory, and will enable him to find the account given of its history clear, easy, and interesting.

Having thus defined what the pupa state is, let us take up one of these withered objects, and by a little gentle treatment, with the assistance of a delicate scissors, a sharp pointed penknife of very keen edge, and two or three pins, we shall succeed in unrolling the insect mummy. In order to obtain the best sight of what the pupa case contains, it will be advisable to select as large a pupa as can be procured. Those of the butterfly tribe are well suited for this purpose. If we are pretty fortunate in our dissections, we shall succeed in discovering, that within the membrane-like skin there is exhibited a beautiful spectacle of order and neatness. The legs, and wings, and other external appendages, are folded down close to the body of the insect. The feet are often crossed smoothly over the breast, and the wings are flattened against the side of the body; the antennæ are also neatly arranged parallel with the legs; and altogether the insect presents a very singular appearance, from the fact of all its organs being thus smoothed down, compressed into the smallest compass, and enveloped by the external skin. The mummy appearance is very striking in some pupæ, as in the specimen figured. The appearance of the folded limbs is indistinctly exhibited in the companion pupa. All the parts of the perfect insect can be distinctly traced, if the pupa is sufficiently matured.

By gently using a fine needle, the wings, antennæ, and legs, can be separated from the side of the body, and made to exhibit somewhat of their natural appearance; but as yet every part is widely different from the corresponding parts in the perfect being. The legs are shapeless, the antennæ are imperfect, and the wings,--those glorious organs of the complete condition,--are as yet devoid of their splendid tints, being of a greyish colour, and exhibiting little resemblance to the elegant form afterwards to distinguish them.

Strange to say, every organ in this pupa is enclosed in a sheath of membrane. The head of the insect is covered by a case; the delicate antennæ, however long or fine, have their cases, or sheaths; even the eyes are provided with them. They exist also upon the trunk, wings, and legs, and _tongue_, or proboscis. These cases must not be mistaken for the general outer case which covers the whole insect; they are separate from that, and cover the organs in question closely, after the manner of a glove.

If we were to open a pupa within a few hours after it had assumed this state, we should find its interior filled with a milky fluid, in the midst of which its future limbs and organs are seen very distinctly, but are as yet in a most fragile, or even half fluid state. At a little later period this fluid disappears, and hardens into a sort of glue, which partly fastens down the tender limbs into their proper position until the appointed time comes for the insect to burst from its sleep and live, and from which the case which covers them is formed. From the account thus given of the contents of the pupa-case, it will be apparent that the pupa possesses, when perfect, all the organs of the complete insect, head, eyes, antennæ, wings, legs, &c., and is in fact only different from it in that it is still inactive to a great extent, and still a prisoner within its cell of membrane. In a little while the bonds which keep it in the tomb will be broken, and the slumberer shall rise a glorious creature to the enjoyment of all the happiness of a new condition of existence.

Perhaps few things would cause a person ignorant of insect life more amazement than if we were to hold before his eyes some of the varieties of pupæ in one hand, and the perfect insect in the other, and were then seriously to assure him that both were the same creatures in reality. "Can it be possible?" he might exclaim. "This dry, brown little mass, with these singular knobs, and this elegant insect with its gaudy wings and delicate figure--these the same being!" Nor when we look at the various figures of pupæ, should we be much surprised at his exclamation. In one of the cases at the British Museum is a very large pupa which we have had engraved, and which is here presented to the reader. In this curious creature the folding up of the limbs is very obvious; and some idea of its strange aspect may be formed from the representation of it here given. The pupæ of several moths are very singular in shape. In some there is a sort of little hook, which sticks out from the head, and seems as if it were intended to hang up the creature by. In others there is a kind of nose attached to the head, giving it a droll appearance. The cause of these protuberances is the long tongue of these moths, which, as it is much longer than their bodies, could not of course be contained in the pupa case, unless it was folded up; it is, therefore, neatly folded up and packed into these receptacles, where it is stowed away until, by the insect awakening to active life, this singular instrument becomes necessary to them, when it is withdrawn. The older naturalists, who loved to find out mimicries of all kinds in nature, used to be fond of painting pupæ with human faces, on account of the frequent resemblance to a Roman nose which is found among them. Goedart, a celebrated naturalist, has drawn several, which we are sure will excite the merriment of our readers, and we have therefore shown these remarkable creatures _as represented by him_ in the adjoining cut. One is a respectable-looking old gentleman's face, with his hair brushed up very primly off his forehead. Another resembles a mermaid, for it has the head of a lady, and something like a cap, but its tail is more like that of a fish. The others are quite caricatures. It is the introduction of a dot, to represent the eye, which gives the resemblance to the face in these figures; without it they are by no means strikingly like the face. Madame Merian has favoured us also with some very curious drawings of pupæ of the insects of Surinam, which appear more natural than those of the last author, and present a very fantastic aspect, by reason of the curious projections which stick out from their heads. A few of these are represented below.

As in the case of the larva, so with the pupa; if it is found in a dark situation, it will probably be destitute of colour, or, at any rate, it will only be of a yellowish white: such pupæ, when taken out of their natural hiding-place, and exposed to the sunlight, become of a dark colour. Indeed the majority of pupæ are without any of the gay colouring which distinguishes the previous condition of the insect. It seems as if it had been thought unnecessary to deck in gorgeous raiment the cerements of what we might call "the tomb" of the insect. But there are some beautiful exceptions to this rule. The pupæ of most butterflies, which are suspended in open day, are of a green or yellowish brown colour. Some, however, are painted in fairer colours; and a still greater number are speckled with glittering spots of golden hue, and shine as though gilded with the purest leaves of that precious metal, and burnished. Hence, as before explained, the Latin and Greek terms of _aurelia_ and _chrysalis_ for the pupæ of these insects. The gilding makes them very attractive objects, being applied now in streaks, now in spots, and occasionally,--and this in the very common pupa of the butterfly whose caterpillar, or larva, feeds on the nettle,--they are entirely covered with this splendid coat. The shade of gilding ranges in the depth of its tone from a very pale yellow to the full lustre of virgin gold. No wonder that those who mistook the object of chemistry, in trying to turn all things into gold, were attracted by these glittering things, and actually believed these spots to be of real gold, and hence imagined that they had found out an argument in nature for the transmutation of common metals into that coveted one. But a little experiment, which it is in the power of any one to perform, would soon have undeceived them, and taught them the truth of the proverb, "All is not gold that glitters." By infusing a portion of saffron in hot water, and straining it off after a little time, and adding to the rich yellow liquor thus obtained a few lumps of pure gum Arabic, a sort of gilding varnish will be obtained, which, if applied to a bright shilling, will give it very much of a golden appearance, owing to the shining of the metal showing through a transparent film of a golden colour. The gilded look of the pupa was found by Réaumur to be produced in the same way by the shining white membrane of the inner skin showing through the outer skin, which is of a transparent yellow.

In the Transactions of the Linnæan Society for 1833, the Rev. L. Guilding describes a very curious pupa, the case of which resembles pearl. These little bodies are found in abundance in the island of Antigua, and are often sent home to Europe, under the name of "ground-pearl," as distinguished from the ordinary fishery-pearl. They are devoured by turkeys, and fowls, until the birds are nearly choked with them, when the remedy is to pour vinegar down the throat, which dissolves the pearls, and sets the poor bird at ease. They are strung into necklaces and purses by the ladies of the Bahamas. They long caused much perplexity to naturalists; but they were ultimately found to be really only the pupæ of a little insect which appears to infest the ants, those voracious creatures, and thus to keep down their numbers. A representation of the ground-pearl, and the insect within, is annexed.