The fairy tales of science/Metamorphoses
"There is a difference between a grub and butterfly; yet
Your butterfly was a grub."—Coriolanus.
Once upon a time an aged butterfly, with wings all crumpled and torn, crawled up the stem of a willow, and seated himself on the nearest leaf.
"My last moments are drawing near," said he, "but I do not repine, for life has become a burden to me. My wings are useless, my joints stiff and rheumatic, and my antennae have long since lost their exquisite sensibility. It is quite evident that my flying days are over, but so much happiness has fallen to my share, that I have no right to complain." The butterfly had scarcely finished this soliloquy, when a large tiger-moth alighted on a leaf close by.
"Ah, my friend!" exclaimed the moth, "I am truly glad to see you; I have not many hours to live, and I wish to make you my executor. Do not start, my friend, I am old and decrepit, and you shall see me meet death with becoming resignation."
The butterfly smiled sadly, and declined the proffered executorship, explaining to the venerable tiger-moth that he himself was about to die.
Now, by one of those wonderful coincidences peculiar to fairy tales, a dragon-fly, a gnat, and two small flies, all bowed down by weight of years, settled in the neighbourhood of the two lepidoptera. After much mutual condolence, the six insects began to quarrel about their respective adventures, each bragging that he had seen far more wonderful things than had any of his companions. The dragon-fly became very much excited, and though very feeble, he clashed his mandibles together in a manner that filled the smaller insects with dismay. The butterfly, who was an insect of a very superior turn of mind, put an end to this disagreeable scene.
"My friends," he exclaimed, in a solemn voice, "is it wise to waste the few short hours that remain to us in vain discussion? Would it not be more becoming in old insects like us to sit down quietly, and relate our adventures without quarrelling? Depend upon it, Nature has not formed us differently, and endowed us with distinct faculties, for a mere freak, but because we may be better fitted to enjoy the sweets of life in our separate spheres. Consider, my dear dragon, what pitiable objects you and I would be were we to exchange wings! How could you support your long body with my painted wings, and how could I work your gauzy pinions with my feeble muscles? Instead of boasting about your superior strength and prowess, you ought to accept your gifts with a humble thankfulness, as you must be aware that you are far inferior in point of intellect to the sober bee, or the tiny ant."
"Do not be too hard upon me, Mr. Butterfly," said the great insect; "I own myself in the wrong, and am quite willing to adopt any suggestion you may make with regard to the manner of passing our last hours." The two little flies on hearing their dreaded enemy speak so rationally, instantly recovered their self-possession, and the gnat actually ventured within the reach of his formidable mandibles.
"Well, then," said the butterfly, "let each relate his history in as few words as possible, describing the metamorphoses he has undergone, and the wonderful things that have fallen within the sphere of his observation."
This proposition was received with unanimous approbation, and it was speedily determined that the butterfly should tell the first story.
We will now lay before the reader a true report of the conversation that ensued, adding such explanatory remarks as may be necessary to make the speeches of the insects intelligible.
"I am generally known as the cabbage-butterfly," said the first speaker, "and although my wings are now in a very dilapidated condition, I think you must admit that the dark spots upon the white ground produce a very pretty effect. I need not tell you that I originally came from an egg, which my maternal parent, guided by an unerring instinct, had deposited upon a leaf capable of affording me proper and sufficient nourishment in my caterpillar state. And a beautiful little egg it was, shaped like a flask, marked with fifteen ribs, converging towards the smaller end, and having a delicate yellow colour.
"I was a very little fellow when I made my escape from the egg, but having a tremendous appetite I grew rapidly, and soon became a handsome caterpillar. Nature had furnished me with sixteen feet, and had dressed me in a coat of bluish grey, having a bright yellow line down the back, and another on each side. I am fairly shocked when I think of my voracity, for I frequently devoured double my own weight of cabbage in twenty-four hours. At length, when I had attained my full size, I felt that I was about to undergo a wonderful metamorphosis; accordingly I stole away from the plant on which I had been feeding, and found a secluded corner where I could perform unmolested the tedious and painful operation of wriggling out of my skin.
"Having thrown off my grey coat, and with it my sixteen legs, I became a chrysalis, a mere mummy, in fact, having neither limbs, eyes, nor mouth. My second metamorphosis was even more extraordinary than this. I broke through the mummy cloth as a perfect insect. My wings were at first moist and shrunken, but in an hour or so they spread out to their full extent. I will not attempt to describe the rapture which I experienced in my first flight through the air. My former life seemed to be an ugly dream; and as I flew from flower to flower, sipping ambrosial sweets, I could hardly realize the fact that I had once been a crawling caterpillar, with an insatiable craving for cabbage. The longest life must have an end; and you now see me patiently awaiting death or some new metamorphosis of which my instinct gives me no warning."
The reader will doubtless be astonished to hear that the butterfly exists in the caterpillar, and has been detected in it by expert anatomists. "In order," says Swammerdam, "to discover plainly that a butterfly is enclosed and hidden in the skin of the caterpillar, the following operation must be performed. One must kill a full-grown caterpillar, tie a thread to its body, and dip it for a minute or two into boiling water. The outer skin will, after this, easily separate, because the fluids between the two skins are by this means rarefied and dilated, and therefore they break and detach both the vessels and the fibres wherewith they were united together. By this means the outer skin of the caterpillar, being separated, may be easily drawn off from the butterfly which is contained and folded up in it. This done, it is clearly and distinctly seen that, within this skin of the caterpillar, a perfect and real butterfly was hidden, and therefore the skin of the caterpillar must be considered only as an outer garment, containing in it parts belonging to the nature of a butterfly, which have grown under its defence by slow degrees, in like manner as other sensitive bodies increase by accretion.
"But as these limbs of the butterfly which lie under the skin of a caterpillar cannot without great difficulty be discovered, unless by a person accustomed to such experiments—because they are then very soft, tender, and small, and are, moreover, complicated or folded together, and enclosed in some membranous covering—it is therefore necessary to defer the operation just now proposed until the several parts of the butterfly become somewhat more conspicuous than at first, and are more increased and swelled under the skin by the force of the intruded blood and aqueous humour. This is known to be the case when the caterpillar ceases to eat, and its skin on each side of the thorax, near under the head, is then observed to be more and more elevated by the increasing and swelling limbs, and shows the appearance of two pairs of prominent tubercles." Before this beautiful discovery was made the wildest theories were propounded to explain insect metamorphoses.
When the butterfly had finished his story, the tiger-moth addressed his friends in the following manner:—"I fear that my history will afford you but little interest, as I have undergone a series of changes of precisely the same character as those which have just been described by our friend. In my youthful days I was quite as voracious as the butterfly, but my favourite food was the nettle. My body was covered with long hairs of a dark-brown colour. This woolly coat was of immense service to me; for besides keeping me warm, it saved me many a bruise by breaking my fall when I tumbled off a leaf or branch. Before changing into a chrysalis, I spun for myself a snug little silken hammock, in which I might repose in peace until my final metamorphosis into a moth. There, I have finished my brief narrative, and am now longing to hear the dragon-fly's story, as I suspect it will be very wonderful."
"My early days," said the dragon-fly, "were spent in the water. I was then furnished with six feet, but I did not use them for walking so much as for capturing my prey. I moved through the water by means of a wonderful hydraulic engine, which nature had given me. With this engine I was able to eject a stream of water to the distance of several inches; and this jet propelled me through the water, in consequence of its being resisted by the stationary mass of the fluid behind. I was the terror of all the inhabitants of the pond, for I was dreadfully rapacious, devouring every living thing that came within my reach. In surprising my prey, I approached it very stealthily, and pounced upon it suddenly. I was so artful, that insects, and even small fishes, found it difficult to elude my attacks.
"My first metamorphosis was inconsiderable, as my appearance underwent very little alteration, and I still retained my six legs, and had the same carnivorous propensities as formerly. At length I felt that the term of my aquatic existence had expired, and I therefore crawled up the stem of a water-plant into the air. Having selected a dry spot, I pushed my sharp claws into the soft stem, and awaited my final transformation. By the swelling of the upper part of my body, the outer skin was greatly distended, and was eventually rent asunder on the back of the head and shoulders. Through this opening I escaped as a perfect fly, leaving the empty slough fixed to the aquatic plant. Old age has now come upon me, and I require no further nourishment; but I must confess that I never lost my rapacious instincts. Instead of seeking an innocent nutriment in the pulp of fruits, or the nectar of flowers, I hovered in the air only to pounce upon other insects and crush them with my powerful mandibles. I have exterminated innumerable gnats and flies in my latter days, and have even caused the death of several moths and butterflies."
This confession so alarmed the gnat, that he flew at once to another leaf, so as to be at a safe distance from the splendid blue monster, for whom he had hitherto entertained so little fear. "Do not run away!" exclaimed the dragon-fly, in a very jocular tone. "I shall not eat you until I have heard your story, provided you sit still; but if you attempt to leave this tree, I shall be very much offended, and will not answer for the consequences."
"O, sir!" exclaimed the gnat, "how could you suppose that I should run away from you, the handsomest, the best, and the most magnanimous insect that ever breathed? I moved from the leaf upon which you are sitting, because I felt my own unworthiness so keenly, and feared that my presence might cause you some uneasiness. If you would like to hear the story of my life, I shall be most proud to relate it to you, and to the other illustrious insects that are here assembled.
"I was originally produced from a tiny egg, shaped like a bottle. My mother knew that her offspring would pass the greater portion of their time in water, and she therefore deposited her eggs upon the surface of a pond. Now, as each egg was heavy enough to sink if dropped into water, she glued some three hundred of them together into the form of a boat, which floated so safely that the most violent agitation of the water could not sink it; and, what was still more extraordinary, it never became filled with water, even though exposed to the heavy rains. When hatched, I took the form of a minute, whitish, semi-transparent grub. I usually swam near the surface of the water, with my head downwards and my tail in the air for my breathing organs were situated in the tail, and not along the sides, as in caterpillars. In course of time I underwent a semi-transformation, like that of our noble friend the dragon, and ten days after I broke through the skin that covered me, and winged my way through the air."
The reader would probably like to hear how the gnat escapes from its envelope, without wetting its wings. The most important, and indeed indispensable part of the mechanism, is the maintaining of its upright position while extricating itself from the skin. The envelope, as it is thrown off, forms a life-boat, and supports the gnat until it gets its wings set at liberty and trimmed for flight. The body of the insect serves this little boat for a mast. "When the naturalist," says Reaumur, "observes how deep the prow of the tiny boat dips into the water, he becomes anxious for the fate of the little mariner, particularly if a breeze ripple the surface, for the least agitation of the air will waft it rapidly along, since its body performs the duty of a sail as well as of a mast; but as it bears a much greater proportion to the little bark than the largest sail does to a ship, it appears in great danger of being upset, and once laid on its side all is over. I have sometimes seen the surface of the water covered with the bodies of gnats which had perished in this way; but for the most part all terminates favourably, and the danger is instantly over." When the gnat has extricated all but the tail, it stretches out its two fore-legs, and then the middle pair, bending them down to feel for the water, upon which it is able to walk as upon dry land, the only aquatic faculty which it retains after having winged its way above the element where it spent the first stages of its existence.
The larger of the two flies came forward as soon as the gnat had done speaking, and gracefully waving his antennae, addressed the assembled insects as follows:—"I am a water-fly, and, like the last two speakers, I spent my youth at the bottom of a pond. Having a very soft body, which required some protection from the rapacity of fishes and carnivorous insects, I enclosed myself in a case formed of bits of straw and wood, pebbles, and tiny shells bound together by silken threads, which I spun from my mouth. While I remained in the grub state, this case afforded me sufficient protection; but as soon as I felt a change approaching which I knew would render me helpless and inactive, I thought it advisable to contrive additional security. I therefore wove a silken grating at the entrance of my little gallery. This grating was marvellously strong, for I crossed and recrossed the threads until a thickish circular plate of brown silk was formed, which became as hard as gum. Of course I left a number of openings in this plate, for the purpose of breathing. In this case I reposed in peace until just before my final metamorphosis, when I gnawed my way through the grating with a pair of mandibles specially provided for that one object. I then swam to the surface, and underwent my change into a perfect insect."
"It is my turn now," said the other fly, a tiny creature with a black body and yellow legs; "and although I am so small, I think I may safely say that I have led a stranger life than any of you. I did not pass my time, when in my caterpillar state, in looking out for food; yet I lived on the fat of the land. I am the dreaded ichneumon-fly, and the egg from which I was produced was deposited by my mother in the soft body of a cabbage-caterpillar, the brother probably of our friend here with the ragged wings. My kind parent settled upon the caterpillar's back, and pierced the skin in about thirty places, depositing an egg in each wound. When we were all hatched, we set to work devouring the fatty portions of the caterpillar, who continued to eat as usual, though his food did not afford him much nourishment. When full grown, we eat our way through the skin of the unfortunate cabbage-feeder, and immediately spun for ourselves a number of little silken cocoons of a bright yellow colour, in which to pass the winter. In one of these little cocoons I underwent my transformations, and when I escaped I had the form which you now behold!"
Such, reader, is the subject of a conversation which took place, or might have taken place, on the leaves of the willow, between six of our commonest insects. The metamorphoses of insects surely deserve a place in the fairy tales of Science, as they are far more wonderful, because true, than any of the metamorphoses that we read of in the fairy tales of Greece and Rome.
- The order Lepidoptera, or scaly wings, includes butterflies and moths.
- A Greek term, signifying golden, applied to pupæ on account of the golden lustre which they sometimes exhibit.