Moths, eggs, caterpillars, winter quarters
If you are too fastidious to read this chapter, it will be your permanent loss, for it contains the life history, the evolution of one of the most amazingly complicated and delicately beautiful creatures in existence. There are moths that come into the world, accomplish the functions that perpetuate their kind, and go out, without having taken any nourishment. There are others that feed and live for a season. Some fly in the morning, others in the glare of noon, more in the evening, and the most important class of big, exquisitely lovely ones only at night. This explains why so many people never have seen them, and it is a great pity, for the nocturnal, non-feeding moths are birdlike in size, flower-like in rare and complicated colouring, and of downy, silent wing.
The moths that fly by day and feed are of the Sphinginae group, Celeus and Carolina, or Choerocampinae, which includes the exquisite Deilephila Lineata, and its cousins; also Sphingidae, which cover the clear-winged Hemaris diffinis and Thysbe. Among those that fly at night only and take no food are the members of what is called the Attacine group, comprising our largest and commonest moth, Cecropia; also its near relative Gloveri, smaller than Cecropia and oflovely rosy wine-colour; Angulifera, the male greyish brown, the female yellowish red; Promethea, the male resembling a monster Mourning Cloak butterfly and the female bearing exquisite red-wine flushings; Cynthia, beautiful in shades of olive green, sprinkled with black, crossed by bands of pinkish lilac and bearing crescents partly yellow, the remainder transparent. There are also the deep yellow Io, pale blue-green Luna, and Polyphemus, brown with pink bands of the Saturniidae; and light yellow, red-brown and grey Regalis, and lavender and yellow Imperialis of the Ceratocampidae, and their relatives. Modest and lovely Modesta belongs with the Smerinthinae group; and there are others, feeders and non-feeders, forming a list too long to irncorporate, for I have not mentioned the Catocalae family, the fore-wings of which resemble those of several members of the Sphinginae, in colour, and when they take flight, the back ones flash out colours that run the gamut from palest to deepest reds, yellows, and browns, crossed by wide circling bands of black; with these, occasionally the black so predominates that it appears as if the wing were black and the bands of other colour. All of them are so exquisitely beautiful that neither the most exacting descriptions, nor photographs from life, nor water colours faithfully copied from living subjects can do them justice. They must be seen alive, newly emerged, down intact, colours at their most brilliant shadings, to be appreciated fully. With the exception of feeding or refraining from eating, the life processes of all these are very similar.
Moths are divided into three parts, the head, thorax, and abdomen, with the different organs of each. The head carries the source of sight, scent, and the mouth parts, if the moth feeds, while the location of the ears is not yet settled definitely. Some scientists place hearing in the antennae, others in a little organ on each side the base of the abdomen. Packard writes: "The eyes are large and globose and vary in the distance apart in different families": but fails to tell what I want to know most: the range and sharpness of their vision. Another writer states that the eyes are so incomplete in development that a moth only can distinguish light from darkness and cannot discern your approach at over five feet.
This accords with my experience with Cecropia, Polyphemus, Regalis, and Imperialis. Luna either can see better, hear acutely, or is naturally of more active habit. It is difficult to capture by hand in daytime; and Promethea acts as if its vision were even clearer. This may be the case, as it flies earlier in the day than any of the others named, being almost impossible to take by hand unless it is bound to a given spot by sex attraction. Unquestionably the day fliers that feed--the Sphinginae and Choerocampinae groups--have fairly good vision, as also the little "Clear-wings" tribe, for they fly straight to the nectar-giving flowers and fruits they like best to feed upon, and it is extra good luck if you capture one by hand or even with a net. It must be remembered that all of them see and go to a bright light at night from long distances.
Holland writes: "The eyes of moths are often greatly developed," but makes no definite statements as to their range of vision, until he reaches the Catocalae family, of which he records: "The hind wings are, however, most brilliantly coloured. In some species they are banded with pink, in others with crimson; still others have markings of yellow, orange, or snowy white on a background of jet black. These colours are distinctive of the species to a greater or less extent. They are only displayed at night. The conclusion is irresistibly forced upon us that the eyes of these creatures are capable of discriminating these colours in the darkness. We cannot do it. No human eye in the blackness of the night can distinguish red from orange or crimson from yellow. The human eye is the greatest of all anatomical marvels, and the most wonderful piece of animal mechanism in the world, but not all of power is lodged within it. There are other allied mechanisms which have the power of responding to certain forms of radiant energy to a degiee which it does not possess."
This conclusion is not "irresistibly forced" upon me. I do believe, know in fact, that all day-flying, feeding moths have keener sight and longer range of vision than non-feeders; but I do not believe the differing branches of the Catocalae group, or moths of any family, locate each other "in the blackness of night," by seeing markings distinctly. I can think of no proof that moths, butterflies or any insects recognize or appreciate colour. Male moths mate with females of their kind distinctly different from them in colour, and male butterflies pair with albinos of their species, when these differ widely from the usual colouring.
A few moths are also provided with small simple eyes called ocelli; these are placed on top of the head and are so covered with down they cannot be distinguished save by experts. Mueller believes that these are for the perception of objects close to a moth while the compound eyes see farther, but he does not prove it.
If the moth does not feed, the mouth parts are scarcely developed. If a feeder, it has a long tongue that can be coiled in a cleft in the face between the palpi, which Packard thinks were originally the feelers. This tongue is formed of two grooved parts so fastened together as to make a tube through which it takes flower and fruit nectar and the juices of decaying animal matter.
What are thought by some to be small organs of touch lie on either side the face, but the exact use of these is yet under discussion, It is wofully difficult to learn some of these things.
In my experience the antennae, are the most sensitive, and therefore the most important organs of the head--to me. In the Attacine group these stand out like delicately cut tiny fern fronds or feathers, always being broader and more prominent on the male. Other families are very similar and again they differ widely. You will find moths having pointed hair-like antennae; others heaviest at the tip in club shape, or they may be of even proportion but flat, or round, or a feathered shaft so fine as to be unnoticed as it lies pressed against the face. Some writers say the antennae are the seat of scent, touch, and hearing. I had not thought nature so impoverished in evolving her forms as to overwork one delicate little organ for three distinct purposes. The antennae are situated close where the nose is, in almost every form of life, and I would prefer to believe that they are the organs of scent and feeling. I know a moth suffers most over any injury to them; but one takes flight no quicker or more precipitately at a touch on the antennae than on the head, wing, leg, or abdomen.
We are safe in laying down a law that antennae are homologous organs and used for identical purposes on all forms of life carrying them. The short antennae of grasshoppers appear to be organs of scent. The long hair-fine ones of katydids and crickets may be also, but repeatedly I have seen these used to explore the way ahead over leaves and limbs, the insect feeling its path and stepping where a touch assures it there is safe footing. Katydids, crickets, and grasshoppers all have antennae, and all of these have ears definitely located; hence their feelers are not for auricular purposes. According to my logic those of the moth cannot be either. I am quite sure that primarily they serve the purpose of a nose, as they are too short in most cases to be of much use as `feelers,' although that is undoubtedly their secondary office. If this be true, it explains the larger organs ofthe male. The female emerges from winter quarters so weighted with carrying from two to six hundred eggs, that she usually remains and develops where she is. This throws the business of finding her location on the male. He is compelled to take wing and hunt until he discovers her; hence his need of more acute sense of scent and touch. The organ that is used most is the one that develops in the evolution of any form of life.
I can well believe that the antennae are most important to a moth, for a broken one means a spoiled study for me. It starts the moth tremulously shivering, aimlessly beating, crazy, in fact, and there is no hope of it posing for a picture. Doctor Clemens records that Cecropia could neither, walk nor fly, but wheeled in a senseless, manner when deprived of its antennae. This makes me sure that they are the seat of highest sensibility, for I have known in one or two cases of chloroformed moths reviving and without struggle or apparent discomfort, depositing eggs in a circle around them, while impaled to a setting board with a pin thrust through the thorax where it of necessity must have passed through or very close the nervous cord and heart.
The moth is covered completely with silken down like tiny scales, coloured and marked according to species, and so lightly attached that it adheres to the cocoon on emergence and clings to the fingers at the lightest touch. From the examination of specimens I have taken that had disfigured themselves, it appears that a moth rubbed bare of down would seem as if covered with thinly cut, highly polished horn, fastened together in divisions. This is called `chitine' by scientists.
The thorax bears four wings, and six legs, each having five joints and ending in tiny claws. The wings are many-veined membranous sacs, covered with scales that are coloured according to species and arranged to form characteristic family markings. They are a framework usually of twelve hollow tubes or veins that are so connected with the respiratory organs as to be pneumatic. These tubes support double membranes covered above and below with down. At the bases of the wings lie their nerves. The fore-wings each have a heavy rib running from the base and gradually decreasing to the tip. This is called the costa. Its purpose is to bear the brunt of air-pressure in flight. On account of being compelled to fly so much more than the females, the back wings of the males of many species have developed a secondary rib that fits under and supports the front, also causing both to work together with the same impulse to flight. A stiff bunch of bristles serves the same purpose in most females, while some have a lobe extending from the fore-wing. As long as the costa remains unbroken to preserve balance, a moth that has become entangled in bushes or suffered rough treatment from birds can fly with badly damaged wing surfaces.
In some species, notably the Attacine group and all non-feeding, night-flying moths, the legs are short, closely covered with long down of the most delicate colours of the moth, and sometimes decorated with different shades. Luna has beautiful lavender legs, Imperialis yellow, and Regalis red-brown. The day-flying, feeding group have longer, slenderer legs, covered with shorter down, and carry more elaborate markings. This provision is to enable them to cling firmly to flower or twig while feeding, to help them to lift the body higher, and walk dextrously in searching for food. It is also noticeable that these moths have, for their size, comparatively much longer, slenderer wings than the non-feeders, and they can turn them back and fold them together in the fly position, thus enabling them to force their way into nectar-bearing flowers of trumpet shape.
The abdomen is velvet soft to the touch, and divided into rings called segments, these being so joined that this member can be turned and twisted at will. In all cases the last ring contains the sex organs. The large abdomen of the female carries several hundred embryo eggs, and that of the male the seminal fluid.
Much has been written of moths being able to produce odours that attract the sexes, and that are so objectionable as to protect them from birds, mice, and bats. Some believe there are scent glands in a few species under the wing scales. I have critically examined scores of wings as to colour markings, but never noticed or smelled these. On some, tufts of bristlelike hairs can be thrust out, that give a discernible odour; but that this carries any distance or is a large factor in attracting the sexes I do not believe so firmly, after years of practical experience, as I did in the days when I had most of my moth history from books. I have seen this theory confounded so often in practice.
In June of 1911, close six o'clock in the evening, I sat on the front veranda of the Cabin, in company with my family, and watched three moths sail past us and around the corner, before I remembered that on the screen of the music-room window to the east there was a solitary female Promethea moth, that day emerged from a cocoon sent me by Professor Rowley. I hurried to the room and found five male moths fluttering before the screen or clinging to the wild grape and sweet brier vines covering it. I opened the adjoining window and picked up three of the handsomest with my fingers, placing them inside the screen. Then I returned to the veranda.
Moths kept coming. We began studying the conditions. The female had emerged in the diningroom on the west side of the cabin. On account of the intense heat of the afternoon sun, that side of the building had been tightly closed all day. At four o'clock the moth was placed on the east window, because it was sheltered with vines. How soon the first male found her, I do not know. There was quite a stiff evening breeze blowing from the west, so that any odour from her would have been carried on east. We sat there and watched and counted six more moths, every one of which came down wind from the west, flying high, above the treetops in fact, and from the direction of a little tree-filled plot called Studabaker's woods. Some of them we could distinguish almost a block away coming straight toward the Cabin, and sailing around the eastern corner with the precision of hounds on a hot trail. How they knew, the Almighty knows; I do not pretend to; but that there was odour distilled by that one female, practically imperceptible to us (she merely smelled like a moth), yet of such strength as to penetrate screen, vines, and roses and reach her kind a block away, against considerable breeze, I never shall believe.
The fact is, that moths smell like other moths of the same species, and within a reasonable radius they undoubtedly attract each other. In the same manner birds carry a birdlike odour, and snakes, frogs, fish, bees, and all animals have a scent peculiar to themselves. No dog mistakes the odour of a cat for that of another dog. A cow does not follow the scent of horses to find other cattle. No moth hunts a dragon-fly, a butterfly, or in my experience, even a moth of another species in its search for a mate. How male moths work the miracles I have seen them accomplish in locating females, I cannot explain. As the result of acts we see them perform, we credit some forms of life with much keener scent than others, and many with having the power more highly developed than people. The only standard by which we can determine the effect that the odour of one insect, bird, or animal has upon another is by the effect it has upon us. That a male moth can smell a female a block away, against the wind, when I can detect only a faint musky odour within a foot of her, I do not credit.
Primarily the business of moths is to meet, mate, and deposit eggs that will produce more moths. This is all of life with those that do not take food. That they add the completing touch and most beautiful form of life to a few exquisite May and June nights is their extra good fortune, not any part of the affair of living. With moths that feed and live after reproduction, mating and egg placing comes first. In all cases the rule is much, the same. The moths emerge, dry their wings, and reach full development the first day. In freedom, the females being weighted with eggs seldom attempt to fly. They remain where they are, thrust out the egg placer from the last ring of the abdomen and wait. By ten o'clock the males, in such numbers as to amaze a watcher, find them and remain until almost morning. Broad antennae, slenderer abdomen, and the claspers used in holding the female in mating, smaller wings and more brilliant markings are the signs by which the male can be told in most cases. In several of the Attacine group, notably Promethea, the male and female differ widely in markings and colour. Among the other non-feeders the difference is slight. The male Regalis has the longest, most gracefully curved abdomen and the most prominent claspers of any moth I ever examined; but the antennae are so delicate and closely pressed against the face most of the time as to be concealed until especially examined. I have noticed that among the moths bearing large, outstanding antennae, the claspers are less prominent than with those having small, inconspicuous head parts. A fine pair of antennae, carried forward as by a big, fully developed Cecropia, are as ornamental to the moth as splendidly branching antlers are to the head of a deer.
The female now begins egg placing. This requires time, as one of these big night moths deposits from three hundred and fifty to over six hundred eggs. These lie in embryonic state in the abdomen of the female. At her maturity they ripen rapidly. When they are ready to deposit, she is forced to place them whether she has mated or not. In case a mate has found her, a small pouch near the end of her abdomen is filled with a fluid that touches each egg in passing and renders it fertile. The eggs differ with species and are placed according to family characteristics. They may be pure white, pearl-coloured, grey, greenish, or yellow. There are round, flat, and oblong eggs. These are placed differently in freedom and captivity. A moth in a natural location glues her eggs, often one at a time, on the under or upper side of leaves. Sometimes she dots several in a row, or again makes a number of rows, like a little beaded mat. One authority I have consulted states that "The eggs are always laid by the female in a state of freedom upon the food-plant which is most congenial to the larvae." This has not 'always' been the case in my experience. I have found eggs on stone walls, boards, fences, outbuildings, and on the bark of dead trees and stumps as well as living, even on the ground. This also, has been the case with the women who wrote "Caterpillars and their Moths", the most invaluable work on the subject ever compiled.
A captive moth feels and resents her limitations. I cannot force one to mate even in a large box. I must free her in the conservatory, in a room, or put her on an outside window br door screen. Under these conditions one will place her eggs more nearly as in freedom; but this makes them difficult to find and preserve. Placed in a box and forced by nature to deposit her eggs, as a rule, she will remain in one spot and heap them up until she is forced to move to make room for more. One big female Regalis of the last chapter of this book placed them a thimbleful at a time; but the little caterpillars came rolling out in all directions when due. In my experience, they finish in four or five nights, although I have read of moths having lived and placed eggs for ten, some species being said to have deposited over a thousand. Seven days is usually the limit of life for these big night moths with me; they merely grow inactive and sluggish until the very last, when almost invariably they are seized with a muscular attack, in which they beat themselves to rags and fringes, as if resisting the overcoming lethargy. It is because of this that I have been forced to resort to the gasoline bottle a few times when I found it impossible to paint from the living moth; but I do not put one to sleep unless I am compelled.
I never have been able to induce a female to mate after confinement had driven her to begin depositing her eggs, not even under the most favourable conditions I could offer, although others record that they have been so fortunate. Repeatedly I have experimented with males and females of different species, but with no success. I have not seem a polygamous moth; but have read of experiences with them.
Sometimes the eggs have a smooth surface, again they may be ridged or like hammered brass or silver. The shells are very thin and break easily. At one side a place can be detected where the fertilizing fluid enters. The coming caterpillar begins to develop at once and emerges in from six to thirty days, with the exception of a few eggs placed in the fall that produce during the following spring. The length of the egg period differs with species and somewhat with the same moths, according to suitable or unfavourable placing, and climatic conditions. Do not accept the experience of any one if you have eggs you very much desire to be productive of the caterpillars of rare moths; after six days take a peep every day if you would be on the safe side. With many species the shells are transparent, and for the last few days before emergence the growth of the little caterpillars can be watched through them.
When matured they break or eat a hole in their shells and emerge, seeming much too large for the space they occupied. Family characteristics show at once. Many of them immediately turn and eat their shells as if starving; others are more deliberate. Some grace around for a time as if exercising and then return and eat their shells; others walk briskly away and do not dine on shell for the first meal. Usually all of them rest close twenty-four hours before beginning on leaves. Once they commence feeding in favourable conditions they eat enormously and grow so rapidly they soon become too large for their skins to hold them another instant; so they pause and stop eating for a day or two while new skin forms. Then the old is discarded and eaten for a first meal, with the exception of the face covering. At the same time the outer skin is cast the intestinal lining is thrown off, and practically a new caterpillar, often bearing different markings, begins to feed again.
These moults occur from four to six times in the development of the caterpillar; at each it emerges larger, brighter, often with other changes of colour, and eats more voraciously as it grows. With me, in handling caterpillars about which I am anxious, their moulting time is critical. I lost many until I learned to clean their boxes thoroughly the instant they stopped eating and leave them alone until they exhibited hunger signs again. They eat greedily of the leaves preferred by each species, doing best when the foliage is washed and drops of water left for them to drink as they would find dew and rain out of doors. Professor Thomson, of the chair of Natural History of the University of Aberdeen, makes this statement in his "Biology of the Seasons", "Another feature in the life of caterpillars is their enormous appetite. Some of them seem never to stop eating, and a species of Polyphemus is said to eat eighty-six thousand times its own weight in a day." I notice Doctor Thomson does not say that he knows this, but uses the convenient phrase, "it is said." This is an utter impossibility. The skin of no living creature will contain eighty-six thousand times its own weight in a day. I have raised enough caterpillars to know that if one ate three times its own weight in a day it would have performed a skin- stretching feat. Long after writing this, but before the manuscript left my hands, I found that the origin of this statement lies in a table compiled by Trouvelot, in which he estimates that a Polyphemus caterpillar ten days old weighs one half grain, or ten times its original weight; at twenty days three grains, or sixty times its first weight; and so on until at fifty-six days it weighs two hundred and seven grains, or four thousand one hundred and forty times its first weight. To this he adds one half ounce of water and concludes: "So the food taken by a single silkworm in fifty-six days equals in weight eighty-six thousand times the primitive weight of the worm." This is a far cry from eating eighty-six thousand times its own weight in a day and upholds in part my contention in the first chapter, that people attempting to write upon these subjects "are not always rightly informed."
When the feeding period is finished in freedom, the caterpillar, if hairless, must be ready to evolve from its interior, the principal part of the winter quarters characteristic of its species while changing to the moth form, and in the case of non-feeders, sustenance for the lifetime of the moth also. Similar to the moth, the caterpillar is made up of three parts, head, thorax, and abdomen, with the organs and appendages of each. Immediately after moulting the head appears very large, and seems much too heavy for the size of the body. At the end of a feeding period and just previous to another moult the body has grown until the head is almost lost from sight, and it now seems small and insignificant; so that the appearance of a caterpillar depends on whether you examine it before or after moulting.
The head is made up of rings or segments, the same as the body, but they are so closely set that it seems to be a flat, round, or pointed formation with discernible rings on the face before casting time. The eyes are of so simple form that they are supposed only to distinguish light from darkness. The complicated mouth is at the lower part of the head. It carries a heavy pair of cutters with which the caterpillar bites off large pieces of leaf, a first pair of grinders with which it macerates the food, and a second pair that join in forming the under lip. There is also the tube that connects with the silk glands and ends in the spinneret. Through this tube a fluid is forced that by movements of the head the caterpillar attaches where it will and draws into fine threads that at once harden in silk. This organism is sufficiently developed for use in a newly emerged caterpillar, for it can spin threads by which to drop from leaf to leaf or to guide it back to a starting point.
The thorax is covered by the first three rings behind the head, and on it are six legs, two on each segment. The remainder of the caterpillar is abdominal and carries small pro-legs with which to help it cling to twigs and leaves, and the heavy anal props that support the vent. By using these and several of the pro-legs immediately before them, the caterpillar can cling and erect the front part of the body so that it can strike from side to side when disturbed. In the case of caterpillars that have a horn, as Celeus, or sets of them as Regalis, in this attitude they really appear quite formidable, and often I have seen them drive away small birds, while many people flee shrieking.
There are little tubes that carry air to the trachea, as caterpillars have no lungs and can live with a very small amount of air.
The skin may be rough, granulated, or soft and fine as silk, and in almost every instance of exquisite colour: bluish green, greenish blue, wonderful yellows and from pale to deep wine red, many species having oblique touches of contrasting colours on the abdominal rings. Others are marked with small projections of bright colours from which tufts of hair or bristles may grow. In some, as Io, these bristles are charged with an irritating acid that will sting for an hour after coming in contact with the skin, but does no permanent injury. On a few there are what seem to be small pockets of acid that can be ejected with a jerk, and on some a sort of filament that is supposed to distil a disagreeable odour. As the caterpillar only uses these when disturbed, it is safe to presume that they are placed for defence, but as in the case of moths I doubt their efficacy.
Some lepidopterists have thought the sex of a moth could be regulated by the amount of food given the caterpillar; but with my numerous other doubts I include this. It is all of a piece with any attempt at sex regulation. I regard it as morally certain that sex goes back to the ovary and that the egg produced yields a male or female caterpillar in the beginning. I am becoming convinced that caterpillars recognize sex in each other, basing the theory on the facts that in half a dozen instances I have found cocoons, spun only a few inches apart. One pair brought to me as interwoven. Two of these are shown in the following chapter. In all cases a male and female emerged within a few minutes of each other and mated as soon as possible. If a single pair of these cocoons ever had produced two of a kind, it would give rise to doubts. When all of them proved to be male and female that paired, it seems to me to furnish conclusive evidence that the caterpillars knew what they were doing, and spun in the same place for the purpose of appearing together.
At maturity, usually near five weeks, the full-fed caterpillar rests a day, empties the intestines, and races around searching for a suitable place to locate winter quarters. With burrowing caterpillars that winter in pupa cases, soft earth or rotting wood is found and entered by working their way with the heads and closing it with the hind parts. At the desired depth they push in all directions with such force that a hollow larger, but shaped as a hen's egg, is worked out; usually this is six or more inches below the surface. So compactly is the earth forced back, that fall rains, winter's alternate freezing and thawing, always a mellowing process, and spring downpours do not break up the big ball, often larger than a quart bowl, that surrounds the case of the pupa. It has been thought by some and recorded, that this ball is held in place by spinning or an acid ejected by the caterpillar. I never have heard of any one else who has had my luck in lifting these earth balls intact, opening, and photographing them and their contents. I have examined them repeatedly and carefully. I can find not the slightest trace of spinning or adhesion other than by force.
With one of these balls lifted and divided, we decided what happened underground by detaining a caterpillar on the surface and forcing it to transform before us, for this change is not optional. When the time comes the pupa must evolve. So the caterpillar lies on the earth, gradually growing shorter, the skin appearing dry and the horns drooping. There never is a trace of spinning or acid ejected in the sand buckets. When the change is completed there begins a violent twisting and squirming. The caterpillar skin opens in a straight line just behind the head on the back, and by working with the pointed abdomen the pupa case emerges. The cast skin rapidly darkens, and as I never have found a trace of it in an opened earth ball in the spring, I suppose it disintegrates rapidly, or what is more possible, is eaten by small borers that swarm through the top six inches of the earth's crust.
The pupa is thickly coated with a sticky substance that seems to serve the double purpose of facilitating its exit from the caterpillar skin and to dry over it in a glossy waterproof coating. At first the pupa is brownish green and flattened, but as it dries it rapidly darkens in colour and assumes the shape of a perfect specimen. Concerning this stage of the evolution of a moth the doctors disagree.
The emergence I have watched repeatedly, studied photographically, and recorded in the tabulated records from which I wrote the following life histories. At time to appear I believe the pupa bores its way with the sharp point of the abdomen; at least I have seen Celeus, and Carolina, Regalis and Imperialis coming through the surface, abdomen tip first. Once free, they press with the feet against the wing shields, burst them away and leave the case at the thorax. Each moth I ever have seen emerge has been wet and the empty case damp inside. I have poured three large drops of pinkish liquid the consistency of thin cream from the abdominal rings of a Regalis case. Undoubtedly this liquid is ejected by the moth to enable it to break loose from and leave the case with its delicate down intact. The furry scales of its covering are so loosely set that any violent struggle with dry down would disfigure the moth.
Among Cecropia and its Attacine cousins, also Luna, Polyphemus, and all other spinners the process is practically the same, save that it is much more elaborate; most of all with Cecropia, that spins the largest cocoon I ever have seen, and it varies its work more than any of the others. Lengthwise of a slender twig it spins a long, slim cocoon; on a board or wall, roomier and wider at the bottom, and inside hollow trees, and under bridges, big baggy quarters of exquisite reddish tan colours that do not fade as do those exposed to the weather. The typical cocoon of the species is that spun on a fence or outbuilding, not the slender work on the alders or the elaborate quarters of the bridge. On a board the process is to cover the space required with a fine spinning that glues firmly to the wood. Then the worker takes a firm grip with the anal props and lateral feet and begins drawing out long threads that start at the top, reach down one side, across the bottom and back to the top again, where each thread is cut and another begun. As long as the caterpillar can be seen through its work, it remains in the same position and throws the head back and around to carry the threads. I never thought of counting these movements while watching a working spinner, but some one who has, estimates that Polyphemus, that spins a cocoon not one fourth the size of Cecropia, moves the head a quarter of a million times in guiding the silk thread. When a thin webbing is spun and securely attached all around the edges it is pushed out in the middle and gummed all over the inside with a liquid glue that oozes through, coalesces and hardens in a waterproof covering. Then a big nest of crinkly silk threads averaging from three to four inches in length are spun, running from the top down one side, up the other, and the cut ends drawn closely together. One writer states that this silk has no commercial value; while Packard thinks it has. I attach greater weight to his opinion. Next comes the inner case. For this the caterpillar loosens its hold and completely surrounds itself with a small case of compact work. This in turn is saturated with the glue and forms in a thick, tough case, rough on the outside, the top not so solidly spun as the other walls; inside dark brown and worn so smooth it seems as if oiled, from the turning of the caterpillar. In this little chamber close the length and circumference of an average sized woman's two top joints of the first finger, the caterpillar transforms to the pupa stage, crowding its cast skin in a wad at the bottom.
At time for emergence the moth bursts the pupa case, which is extremely thin and papery compared with the cases of burrowing species. We know by the wet moth that liquid is ejected, although we cannot see the wet spot on the top of the inner case of Cecropia as we can with Polyphemus, that does not spin the loose outer case and silk nest. From here on the moths emerge according to species. Some work with their mouths and fore feet. Some have rough projections on the top of the head, and others little sawlike arrangements at the bases of the wings. In whatever manner they free themselves, all of them are wet when they leave their quarters. Sometimes the gathered silk ends comb sufficient down from an emerging Cecropia to leave a terra cotta rim around the opening from which it came; but I never saw one lose enough at this time to disfigure it. On very rare occasions a deformed moth appears. I had a Cecropia with one wing no larger than my thumb nail, and it never developed. This is caused by the moth sustaining an injury to the wing in emergence. If the membrane is slightly punctured the liquid forced into the wing for its development escapes and there is no enlargement.
Also, in rare instances, a moth is unable to escape at all and is lost if it is not assisted; but this is precarious business and should not be attempted unless you are positive the moth will die if you do not interfere. The struggle it takes to emerge is a part of the life process of the moth and quickens its circulation and develops its strength for the affairs of life afterward. If the feet have a steady pull to drag forth the body, they will be strong enough to bear its weight while the wings dry and develop.
All lepidopterists mention the wet condition of the moths when they emerge. Some explain that an acid is ejected to soften the pupa case so that the moth can cut its way out; others go a step farther and state that the acid is from the mouth. I am extremely curious about this. I want to know just what this acid is and where it comes from. I know of no part of the thorax provided with a receptacle for the amount of liquid used to flood a case, dampen a moth, and leave several drops in the shell.
As soon as a moth can find a suitable place to cling after it is out, it hangs by the feet and dries the wings and down. Long before it is dry if you try to move a moth or cause disturbance, it will eject several copious jets of a spray from the abdomen that appears, smells and tastes precisely like the liquid found in the abandoned case. If protected from the lightest touch it will do the same. It appeals to me that this liquid is abdominal, partly thrown off to assist the moth in emergence; something very like that bath of birth which accompanies and facilitates human entrance into the world. It helps the struggling moth in separating from the case, wets the down so that it will pass the small opening, reduces the large abdomen so that it will escape the exit, and softens the case and silk where the moth is working. With either male or female the increase in size is so rapid that neither could be returned to their cases five minutes after they have left them.
It is generally supposed that the spray thrown by a developing moth is for the purpose of attracting others of its kind. I have my doubts. With moths that have been sheltered and not even touched by a breath of wind, this spray is thrown very frequently before the moth is entirely dry, long before it is able to fly and before the ovipositor is thrust out. According to my sense of smell there is very little odour to the spray and what there is would be dissipated hours before night and time for the moths to fly and seek mates. I do not think that the spray thrown so soon after escape from cocoon or case is to attract the sexes, any farther than that much of it in one place on something that it would saturate might leave a general `mothy' odour. Some lepidopterists think this spray a means of defence; if this is true I fail to see why it should be thrown when there is nothing disturbing the moth.
Many of the spinning moths use leaves for their outer foundation. Some appear as if snugly rolled in a leaf and hanging from a twig, but examination will prove that the stem is silk covered to hold the case when the leaf loosens. This is the rule with all Promethea cocoons I ever have seen. Polyphemus selects a cluster of leaves very frequently thorn, and weaves its cocoon against three, drawing them together and spinning a support the length of the stems, so that when the leaf is ready to fall the cocoon is safely anchored. When the winter winds have beaten the edges from the leaves, the cocoon appears as if it were brown, having three ribs with veins running from them, and of triangular shape. Angulifera spins against the leaves but provides no support and so drops to the ground. Luna spins a comparatively thin white case, among the leaves under the shelter of logs and stumps. Io spins so slightly in confinement that the pupa case and cast skin show through. I never have found a pupa out of doors, but this is a ground caterpillar.
Sometimes the caterpillar has been stung and bad an egg placed in its skin by a parasite, before pupation. In such case the pupa is destroyed by the developing fly. Throughout one winter I was puzzled by the light weight of what appeared to be a good Polyphemus cocoon, and at time for emergence amazed by the tearing and scratching inside the cocoon, until what I think was an Ophion fly appeared. It was honey yellow, had antennae long as its extremely long body, the abdomen of which was curved and the segments set together so as to appear notched. The wings were transparent and the insect it seems is especially designed to attack Polyphemus caterpillars and help check a progress that otherwise might become devastating.
Among the moths that do not feed, the year of their evolution is divided into about seven days for the life of the moth, from fifteen to thirty for the eggs, from five to six weeks for the caterpillar and the remainder of the time in the pupa stage. The rule differs with feeding moths only in that after mating and egg placing they take food and live several months, often until quite heavy frosts have fallen.
One can admire to fullest extent the complicated organism, wondrous colouring, and miraculous life processes in the evolution of a moth, but that is all. Their faces express nothing; their attitudes tell no story. There is the marvellous instinct through which the males locate the opposite sex of their species; but one cannot see instinct in the face of any creature; it must develop in acts. There is no part of their lives that makes such pictures of mother-love as birds and animals afford. The male finds a mate and disappears. The female places her eggs and goes out before her caterpillars break their shells. The caterpillar transforms to the moth without its consent, the matter in one upbuilding the other. The entire process is utterly devoid of sentiment, attachment or volition on the part of the creatures involved. They work out a law as inevitable as that which swings suns, moons, and planets in their courses. They are the most fragile and beautiful result of natural law with which I am acquainted.