CHAPTER IV.

VARIETIES AND AGE OF THE PUPA.

Although we are anxious not to attach too much importance to mere names in this little work, and rather to keep the reader's attention fixed upon the really essential truths of the "Life of an Insect," it is expedient that we should mention that while all pupæ may be divided into the two classes, _active_ and _inactive_, yet there are several very striking variations in them, which are more remarkable than those of larvæ. These it is proper here to mention, in order that the reader may be spared the perplexity which would otherwise ensue, were he to imagine that all inactive, or all active pupæ, were pretty much alike. Let it never, however, be forgotten, that it is no matter what the variation in form may be, nor does it matter whether the insect is active or inactive, while in this state of passage from the larva to the perfect form, it is always neither more nor less than a pupa. Through this stage all perfect insects pass, although they may put on various forms and aspects while they are in it, and may possess various, and, perhaps, very opposite faculties during its continuance. If this important fact is borne in mind, there will be no risk of being misled by the confusion of sounds and names, which some have been pleased to encumber insect history with.

In order to form a clear conception of these variations, reference may be made to the engraving on the next page, in which we have caused to be represented the five different kinds of pupæ, as they were named and classified by Linnæus. This plate will sufficiently manifest the necessity of an explanation upon the subject of the variations of pupæ; for few persons in examining it would form the remotest idea, that all the insects there represented are really and truly in the pupa state. Some look so like the perfect insect, that it would be almost impossible for any one only slightly acquainted with insect history to believe them to be in what is in reality a transition stage from the larva to the perfect form.

I. The insect, No. 1, is a pupa called the _Complete_, because it is _active_, and has many of the parts of the perfect insect. The pupa of the spider is an instance.

II. The insect, No. 2, is a pupa called the _Half-complete_, or semi-complete. It is also active, resembles the perfect insect, but has only the rudiments of wings. The grasshopper is an instance of this kind of pupa.

III. The insect, No. 3, is a pupa called the _Incomplete_. It is _inactive_, but possesses rudiments of legs and wings. The common wasp is represented as an example of this kind.

IV. The insect, No. 4, is a pupa called the _Obtected_.[K] This pupa has its upper portion encased in the peculiar manner represented, the chest and lower portion being distinct. The butterfly pupa belongs to this division.

V. The insect, No. 5, is a pupa called the _Coarctate_.[L] In this case the pupa is enclosed within its larva skin, which forms a globular or oval case, the pupa lying loosely in it as if it had shrunk to a smaller size. The pupa of the blow-fly is an example.

Such are the five variations of pupæ, as they were recognised by Linnæus--the _Complete_, _Half-complete_, _Incomplete_, _Obtected_, and _Coarctate_. They are sufficiently minute for ordinary purposes: and it will possibly save the reader some confusion of ideas to endeavour to fix them in the memory; so that when looking at an insect whose pupa state may not be so very characteristic as that of the blow-fly, or butterfly, he may still be able to say with confidence, that although it is unlike these, it is nevertheless a pupa. On all subjects nothing is of so much importance as clearness of ideas. It is better to know only a few things, and to understand them clearly, than to have a confused and indistinct knowledge of a great number. It has been, therefore, simply and entirely with a view to obviate this state of things in the mind, that these definitions of the different kinds of pupæ, which may have appeared not altogether interesting, have been given.

Having fulfilled this duty, we may now proceed to the more agreeable task of ascertaining some interesting facts relative to the insect's life and age in the pupa state. We have already seen that the insect in the larva state often arrives at a very respectable old age; indeed, in this state insects live longer than either in the pupa or perfect states. But pupæ also attain to a very fair number of days, sometimes living as long as two years in that state. Often, however, they are not more than a few days in this condition, and the insect, after a short repose, springs forth a new and active being. But it has been found that insects live a longer or shorter period in the pupa state according as the temperature of the air is cold or hot. Thus, for example, when the larva of a moth has become a pupa in the early part of summer, the pupa state will generally not last beyond a fortnight. But if, on the other hand, the larva becomes a pupa late in the autumn, the pupa state will last until June in the next year: thus manifestly teaching us that according as the weather is mild and genial the pupa state will be shortened; or according as it is cold and rigorous it will be increased in duration. The ingenious Réaumur determined to put these singular facts to an experimental test; and as his results are in the highest degree interesting and important, we shall proceed to submit an abstract of them to the reader's notice.

In casting about for the means of exposing the pupæ he was about to experiment on, to a warm and equable temperature, Réaumur determined to conduct his first experiments in the Royal Conservatories, which were always carefully heated, and in which, as he with French _naïveté_ expresses it, "summer reigned in the depths of winter." In the month of January he carried thither a number of boxes containing pupæ of different species. The result was precisely what he had expected:--in the midst of a severe winter a number of butterflies appeared in his boxes, many of which would not naturally have made their appearance until the months of May, August, or even September; thus shortening the pupa state from four, seven, or eight months, to a fortnight, or to five, or to six weeks in different instances. Five or six days seemed to be equal to a month of the natural temperature. The butterflies thus developed were in no respect different from those which are brought into activity at the natural period. They were as active and perfect, as if their time and place of birth had been the green fields, instead of amidst the strange vegetation of these splendid Conservatories. Several of the mother insects deposited their eggs, accomplishing the last act of their existence as if summer had come, and died while the frosts and snow held all external nature yet in bondage. Not only, therefore, was the duration of the pupa state in these insects shortened, but their whole life was thus abridged by several months.

In November of the same year Réaumur recommenced his experiments, and again exposed a number of pupæ to the genial influence of these hot-houses. The result was the same. In the first week in December butterflies appeared, which would not, in natural circumstances, have been developed earlier than the May of the next year. There were some pupæ, in particular, whose development he watched with great interest. These pupæ belonged to a beautiful species of moth, which has two broods in a year; that is, it lays eggs in May which become butterflies in July, and then again lays eggs which become pupæ in August or September, but do not become butterflies until the following June. He was curious to see whether this second brood, instead of waiting for several months, would, like the first, disclose its butterflies in a considerably shorter time, now that it was exposed to the warmth of the Conservatory. Such actually proved to be the case; and thus two generations of these butterflies were obtained in one year. Alluding to the depredations of caterpillars, he quaintly remarks, "This certainly is not a secret which appears very profitable at present; but who can tell whether that which is useless to us to-day, may not possibly become of value to-morrow? Could we discover some new species of larvæ which would supply us with as good a silk as that of the silk-worm, and might be more easy to rear, but which only produced one generation in each year, and if it lived upon leaves which could be found all the year through, we might avail ourselves of this means of increasing the number of its broods." This remark deserves much consideration.

He was now anxious to try whether, by applying a more equable method of warming, he could succeed in hatching pupæ as he had done in the hothouse. The idea occurred to him of endeavouring to hatch them _under a hen_. He concluded that the warmth of the mother's breast would quite as easily hatch the insects, as it does the eggs. But there was this obstacle in the way: How could he prevent the fragile and tender bodies of the insect pupæ from being crushed and killed by the weight of the hen's body? and, as we would also suggest, How could he ensure that the bird would not actually have eaten up the objects of his care? Aware of the fact, that, when a hen is in the humour to sit, she will often allow smooth stones to be placed among her own eggs, he anticipated no difficulty on that score, and he hit upon the following ingenious experiment:--He procured some hollow glass balls which he had caused to be made as nearly as possible similar in size and shape to the eggs themselves. Into these, by an opening at one end, he introduced seven or eight pupæ, and stopped the mouth up with a cork, but so as to allow a free communication with the external air by paring off a piece from the side of the cork.

Thus prepared, he put the glass egg together with the others in the nest. The hen was a little more sensible than Réaumur had given her credit for; and though she did not thrust the egg out of her nest, she removed it to the outside, where she was so obliging as to permit it to remain; and as it was here just as warm as if it had been in the centre of the eggs, Réaumur did not attempt to interfere with her arrangements. A great deal of moisture arose from the bodies of the pupæ, and condensed like dew on the sides of the glass; but after a day or two this disappeared. The reader may now be anxious to learn the result of this experiment. It was equally successful; indeed, it was more so than the preceding, for in the afternoon of the _tenth_ day a pretty little butterfly was seen within his glass egg, being the first that had appeared of the eight pupæ, and the first ever hatched under the bosom of a hen! The remaining pupæ, all but two, appeared soon after; these two died. Perhaps the warmth of their glassy cell was too violent for them, for it was found by the thermometer to be two or three degrees above blood heat. The whole six pupæ were born in less than six days, while others of the same species in a box in a window-seat were not developed until twelve days later. As the heat thus obtained seemed too violent for pupæ to be artificially reared with success, Réaumur suggests that many variations might be made in the experiments, which would have the effect of moderating its amount. These experiments decided in the most satisfactory manner the quickening influence of increased warmth upon the pupæ of insects. Réaumur now became anxious to try the effects of the opposite state of temperature, and to ascertain whether exposure to cold would exercise any effect upon the pupæ. It was reasonable to imagine that as warmth had hastened forward their development, cold would retard it.

Réaumur determined to try what would be the result of putting his pupæ in their boxes in a cellar, and taking proper care to preserve them from the damps of such a situation. He put them there about the end of January. In ordinary circumstances these pupæ would have become butterflies in the month of July in the same year. July came, and we can conceive the curiosity with which the ingenious experimenter went down, as he tells us, to his cellars, to see if any change had taken place in the pupæ. July passed away; August also passed by, yet the pupæ still slumbered on in their original form. Réaumur left Paris in September, and did not return until the November following. He immediately went in quest of his pupa-charge, and found them still unaltered. Were they dead? Placing one in his hand, it soon began to exhibit such symptoms of motion as plainly showed that it was alive. Winter closed over them still in the pupa form. The spring of the next year dawned upon them, but they were insensible to its influences. "And even now," cries Réaumur, in the month of August, just two years from the time they left the larva form and became pupæ, "they are in perfect health, in excellent condition, and would all become butterflies very soon if I were only to expose them to a warm summer's influence."

"These extraordinary facts," observe Messrs. Kirby and Spence, "lead us to a very singular and unexpected conclusion,--that we have the power of lengthening or shortening the life of many insects at pleasure--that we can cause one individual to live more than twice as long as another of the same species, and _vice versâ_. Had Paracelsus made this discovery, it would have led him to pursue his researches after the elixir of immortality with redoubled confidence, and would have supplied him with an argument for the possibility of prolonging the life of man beyond its usual term, which his sceptical opponents would have found some difficulty in rebutting. Even the logical Réaumur seems inclined to infer from it, that this object of the alchemist's was not so chimerical as we are wont to conclude. He confesses, however, that, if it were to be attained only by the same process as effects the extension of an insect's life,--by prolonging its state of torpor and insensibility,--few would choose to enjoy it on such conditions. The man of pleasure might, perhaps, not object to a sleep of a hundred years, in the hope of finding something new under the sun when he awakened; and an ardent astronomer would probably commit himself with scientific joy to a repose as long and as sound as that of the Seven Sleepers, for the chance of viewing his predicted return of a comet on stepping out of his cave. But ordinary mortals would consign themselves to the perils of so long a night with reluctance, apprehending a fate no better than that which befel the magician who ordered himself to be cut in small pieces and put in pickle, with the expectation of becoming young again."

But this is in every respect erroneous as a deduction from these experiments on insects. It must not be forgotten, that these experiments were made at a time of the insect's life when it is naturally torpid, and not upon the perfect insect. Had Réaumur attempted to prolong the life of a butterfly, he would have failed completely, that is, if he had adopted the same means; so that all which we can infer from these results is simply this, that we can only prolong or shorten the pupa state, which is a state of torpidity, a kind of half-way between life and death.[M] The human frame knows no such state after birth as can be properly compared to the inactive pupa state of insects; and consequently all reasoning founded on what may take place in such a state under the particular circumstances described, is without foundation. Besides all this, God has himself fixed a limit to human life; and we are expressly assured by his word of truth, that "it is appointed unto man once to die;" and though by reason of strength we may reach far into a long life, yet the hour comes at last, and the green earth closes over the only mortal portion of a man. Undoubtedly had Réaumur prolonged his experiments, he would have found that death, or the transformation of the pupa, would ultimately have taken place.

As yet, we are not aware that any practical results on a large scale have followed from Réaumur's interesting experiments. It has been already remarked, that in countries where the silk-worm is reared, it is the custom to hasten the hatching of the eggs by women carrying little packets of them about their person. But this is only to bring forward the development of the larva state. Perhaps the time anticipated by Réaumur may arrive, when insects may be hatched under hens! or in hatching machines, so as to obtain two instead of one brood of eggs and larvæ in a season. Réaumur suggests that the great and wealthy who have good hot-houses, might give all the appearance of summer to them by introducing pupæ in winter, which would soon be hatched, and butterflies or other insects might be seen flying about in December or January, from flower to flower! But he forgot that gardeners generally are rather averse to the presence of insects at all, and particularly to the all-devouring larvæ of many species of butterflies, which would soon commit sad havoc among their choicest plants. We may recommend such experiments to the reader as highly interesting and easy of performance in a common sitting-room, where a fire is kept in winter, with no other apparatus than a tin-box, or a glass jar of very moderate size; even a pill-box would answer every purpose.

Some curious experiments on pupæ of another kind were also performed by Réaumur. He varnished them over with various varnishes, and found that the pupæ thus varnished were developed several weeks later than others of the same species unvarnished. He tried similar experiments upon eggs, and found that the eggs of a hen would keep fresh for a very long period if they were entirely coated with some kind of varnish. This proved a most useful experiment, for it is now common all over the Continent to preserve eggs by covering them either with oil or butter.

We may learn, in reflecting upon the facts brought to light by this ingenious entomologist, with what admirable care and skill the Great Creator has arranged the period to be occupied by the insect in the pupa state. It has been wisely ordained by these arrangements that the insect shall not be developed until the season when its proper food is to be found, or when a proper position for placing its eggs is to be discovered. The gay flutterer, so tender in its frame, must not be born amid the snows of winter, or in the ungenial days of early spring; its pupa, therefore, requires the warm influences of July and August before it will undergo its change. If it were born earlier than that time it would unquestionably perish, and the insect would become extinct; if later, the same result would take place, for it would fall into the killing power of the early winter evenings. As it is, all is well. The insect and the day are made for one another; for it the flower blossoms, and the warm air breathes, and all nature is spread out in warmth and happiness. Its career run through, it departs from the scene it has enlivened, leaving behind, just at the proper time, and in the proper place, the eggs which are to become quickened, live, and die, like itself, all in their appointed time. We thus perceive that it is chiefly the increasing temperature of the air which fixes the time of the insect's duration as a pupa, and sets in movement all the great chain of the events of external nature. In what way an increase of warmth thus acts we are still unable to say; perhaps, indeed, we may never be able to tell. Neither can we understand how it should be, that the principle of life should be ready at a moment's notice to complete its work in the perfection of the insect, and yet held in abeyance by a few degrees of a lower, or quickened into activity by a few degrees higher, temperature. We know that this has been God's doing, and marvellous it is in our eyes; but the wisest of men feels himself ignorant if asked the question, how it is thus arranged? Truly none but a God infinite in wisdom as well as love would take such thought for so humble a creature as a poor insect; but let us not forget that

----"each crawling insect holds a rank Important in the plan of Him who framed This scale of beings,--holds a rank, which, lost, Would break the chain, and leave behind a gap Which Nature's self would rue."

The duration of the insect in the pupa state, though variable, is, without doubt, limited, and sometimes it is fixed to _an hour_, quite irrespective of all external circumstances. The most remarkable example of this kind occurs in the case of the insects whose larva we have already mentioned--the _Ephemera_. These insects appear with the greatest regularity, issuing from the waters of the Seine or Marne, in France, between the 10th and 15th of August. The fishermen call them _manna_; and when their season is come, they say, "the _manna_ begins to appear," or "the manna fell abundantly last night," alluding, by this expression, either to the astonishing quantity of food which the insects afford to the fish, or to the large quantity of fish which they then take. The fishermen expect them with the greatest confidence during these few days, nor are they ever disappointed. Millions upon millions suddenly rise into the air between eight and ten o'clock in the evening, and this generally for three successive nights.[N] Whatever be the temperature of the atmosphere, whether it be cold or hot, these flies invariably appear at the same hour in the evening, that is, between a quarter and half-past eight; towards nine they begin to fill the air; in the following half hour they are in the greatest numbers; and at ten there are scarcely any to be seen. So that in less than two hours--and these always the same--this infinite host of insects leave their pupa state, become perfect insects, perform their appointed work, and vanish. The same phenomenon of regularity of limit to the pupa state occurs also in other insects, though, perhaps, less strikingly. Some insects constantly leave the pupa at break of day; others in the full tide of noon-day, and others when the shadows of declining day come over the landscape. These, however, are certainly exceptions to the general rule, which appears to lay down no precise period of the day or month when this state is ended, and the perfect state is entered upon; but a limit, nevertheless, exists, mainly dependent for its appointment upon the external influences of warmth and air.

This limit attained, we are brought to the next point in the history of the insect pupa. The beautiful organization of the perfect insect has been going on under the dry and repulsive exterior. Its delicate limbs, exquisitely wrought wings, and the other most wonderful organs with which the perfect insect is furnished, are now completed. Nothing remains but to cast off the slough of its pupa case; and it will then be set free to range whither it will in the great atmosphere into which it will emerge. If the reader has been watching these insect changes with the natural object before him, he will immediately confirm our statement, when we mention that it is often possible to tell when the pupa case is about to disclose its occupant. The general form of the limbs is often very clearly to be seen, and the movements of the included insect become much more sensible and conspicuous. If the beautiful gilded pupæ, called, as we have before said, _Chrysalides_, or _Aureliæ_, have been thus nursed with a view to observe their change, it will be noticed that they lose entirely that golden lustre which made them at first such attractive objects. These signs infallibly foretoken the approaching transformation.