Social Life in the Insect World Part 14

Three agents of information affect the senses at a distance: sight, sound, and smell. Can we speak of vision in this connection? Sight could very well guide the arrivals once they had entered the open window; but how could it help them out of doors, among unfamiliar surroundings? Even the fabulous eye of the lynx, which could see through walls, would not be sufficient; we should have to imagine a keenness of vision capable of annihilating leagues of s.p.a.ce. It is needless to discuss the matter further; sight cannot be the guiding sense.

Sound is equally out of the question. The big-bodied creature capable of calling her mates from such a distance is absolutely mute, even to the most sensitive ear. Does she perhaps emit vibrations of such delicacy or rapidity that only the most sensitive microphone could appreciate them?

The idea is barely possible; but let us remember that the visitors must have been warned at distances of some thousands of yards. Under these conditions it is useless to think of acoustics.

Smell remains. Scent, better than any other impression in the domain of our senses, would explain the invasion of b.u.t.terflies, and their difficulty at the very last in immediately finding the object of their search. Are there effluvia a.n.a.logous to what we call odour: effluvia of extreme subtlety, absolutely imperceptible to us, yet capable of stimulating a sense-organ far more sensitive than our own? A simple experiment suggested itself. I would mask these effluvia, stifle them under a powerful, tenacious odour, which would take complete possession of the sense-organ and neutralise the less powerful impression.

I began by sprinkling naphthaline in the room intended for the reception of the males that evening. Beside the female, inside the wire-gauze cover, I placed a large capsule full of the same substance. When the hour of the nocturnal visit arrived I had only to stand at the door of the room to smell a smell as of a gas-works. Well, my artifice failed.

The b.u.t.terflies arrived as usual, entered the room, traversed its gas-laden atmosphere, and made for the wire-gauze cover with the same certainty as in a room full of fresh air.

My confidence in the olfactory theory was shaken. Moreover, I could not continue my experiments. On the ninth day, exhausted by her fruitless period of waiting, the female died, having first deposited her barren eggs upon the woven wire of her cage. Lacking a female, nothing could be done until the following year.

I determined next time to take suitable precautions and to make all preparations for repeating at will the experiments already made and others which I had in mind. I set to work at once, without delay.

In the summer I began to buy caterpillars at a halfpenny apiece.

The market was in the hands of some neighbouring urchins, my habitual providers. On Friday, free of the terrors of grammar, they scoured the fields, finding from time to time the Great Peac.o.c.k caterpillar, and bringing it to me clinging to the end of a stick. They did not dare to touch it, poor little imps! They were thunderstruck at my audacity when I seized it in my fingers as they would the familiar silkworm.

Reared upon twigs of the almond-tree, my menagerie soon provided me with magnificent coc.o.o.ns. In winter a.s.siduous search at the base of the native trees completed my collection. Friends interested in my researches came to my aid. Finally, after some trouble, what with an open market, commercial negotiations, and searching, at the cost of many scratches, in the undergrowth, I became the owner of an a.s.sortment of coc.o.o.ns of which twelve, larger and heavier than the rest, announced that they were those of females.

Disappointment awaited me. May arrived; a capricious month which set my preparations at naught, troublesome as these had been. Winter returned.

The _mistral_ shrieked, tore the budding leaves of the plane-trees, and scattered them over the ground. It was cold as December. We had to light fires in the evening, and resume the heavy clothes we had begun to leave off.

My b.u.t.terflies were too sorely tried. They emerged late and were torpid.

Around my cages, in which the females waited--to-day one, to-morrow another, according to the order of their birth--few males or none came from without. Yet there were some in the neighbourhood, for those with large antennae which issued from my collection of coc.o.o.ns were placed in the garden directly they had emerged, and were recognised. Whether neighbours or strangers, very few came, and those without enthusiasm.

For a moment they entered, then disappeared and did not reappear. The lovers were as cold as the season.

Perhaps, too, the low temperature was unfavourable to the informing effluvia, which might well be increased by heat and lessened by cold as is the case with many odours. My year was lost. Research is disappointing work when the experimenter is the slave of the return and the caprices of a brief season of the year.

For the third time I began again. I reared caterpillars; I scoured the country in search of coc.o.o.ns. When May returned I was tolerably provided. The season was fine, responding to my hopes. I foresaw the affluence of b.u.t.terflies which had so impressed me at the outset, when the famous invasion occurred which was the origin of my experiments.

Every night, by squadrons of twelve, twenty, or more, the visitors appeared. The female, a strapping, big-bellied matron, clung to the woven wire of the cover. There was no movement on her part; not even a flutter of the wings. One would have thought her indifferent to all that occurred. No odour was emitted that was perceptible to the most sensitive nostrils of the household; no sound that the keenest ears of the household could perceive. Motionless, recollected, she waited.

The males, by twos, by threes and more, fluttered upon the dome of the cover, scouring over it quickly in all directions, beating it continually with the ends of their wings. There were no conflicts between rivals. Each did his best to penetrate the enclosure, without betraying any sign of jealousy of the others. Tiring of their fruitless attempts, they would fly away and join the dance of the gyrating crowd.

Some, in despair, would escape by the open window: new-comers would replace them: and until ten o'clock or thereabouts the wire dome of the cover would be the scene of continual attempts at approach, incessantly commencing, quickly wearying, quickly resumed.

Every night the position of the cage was changed. I placed it north of the house and south; on the ground-floor and the first floor; in the right wing of the house, or fifty yards away in the left wing; in the open air, or hidden in some distant room. All these sudden removals, devised to put the seekers off the scent, troubled them not at all. My time and my pains were wasted, so far as deceiving them was concerned.

The memory of places has no part in the finding of the female. For instance, the day before the cage was installed in a certain room. The males visited the room and fluttered about the cage for a couple of hours, and some even pa.s.sed the night there. On the following day, at sunset, when I moved the cage, all were out of doors. Although their lives are so ephemeral, the youngest were ready to resume their nocturnal expeditions a second and even a third time. Where did they first go, these veterans of a day?

They knew precisely where the cage had been the night before. One would have expected them to return to it, guided by memory; and that not finding it they would go out to continue their search elsewhere. No; contrary to my expectation, nothing of the kind appeared. None came to the spot which had been so crowded the night before; none paid even a pa.s.sing visit. The room was recognised as an empty room, with no previous examination, such as would apparently be necessary to contradict the memory of the place. A more positive guide than memory called them elsewhere.

Hitherto the female was always visible, behind the meshes of the wire-gauze cover. The visitors, seeing plainly in the dark night, must have been able to see her by the vague luminosity of what for us is the dark. What would happen if I imprisoned her in an opaque receptacle?

Would not such a receptacle arrest or set free the informing effluvia according to its nature?

Practical physics has given us wireless telegraphy by means of the Hertzian vibrations of the ether. Had the Great Peac.o.c.k b.u.t.terfly outstripped and antic.i.p.ated mankind in this direction? In order to disturb the whole surrounding neighbourhood, to warn pretenders at a distance of a mile or more, does the newly emerged female make use of electric or magnetic waves, known or unknown, that a screen of one material would arrest while another would allow them to pa.s.s? In a word, does she, after her fas.h.i.+on, employ a system of wireless telegraphy? I see nothing impossible in this; insects are responsible for many inventions equally marvellous.

Accordingly I lodged the female in boxes of various materials; boxes of tin-plate, wood, and cardboard. All were hermetically closed, even sealed with a greasy paste. I also used a gla.s.s bell resting upon a base-plate of gla.s.s.

Under these conditions not a male arrived; not one, though the warmth and quiet of the evening were propitious. Whatever its nature, whether of gla.s.s, metal, card, or wood, the closed receptacle was evidently an insuperable obstacle to the warning effluvia.

A layer of cotton-wool two fingers in thickness had the same result. I placed the female in a large gla.s.s jar, and laced a piece of thin cotton batting over the mouth for a cover; this again guarded the secret of my laboratory. Not a male appeared.

But when I placed the females in boxes which were imperfectly closed, or which had c.h.i.n.ks in their sides, or even hid them in a drawer or a cupboard, I found the males arrived in numbers as great as when the object of their search lay in the cage of open wire-work freely exposed on a table. I have a vivid memory of one evening when the recluse was hidden in a hat-box at the bottom of a wall-cupboard. The arrivals went straight to the closed doors, and beat them with their wings, _toc-toc_, trying to enter. Wandering pilgrims, come from I know not where, across fields and meadows, they knew perfectly what was behind the doors of the cupboard.

So we must abandon the idea that the b.u.t.terfly has any means of communication comparable to our wireless telegraphy, as any kind of screen, whether a good or a bad conductor, completely stops the signals of the female. To give them free pa.s.sage and allow them to penetrate to a distance one condition is indispensable: the enclosure in which the captive is confined must not be hermetically sealed; there must be a communication between it and the outer air. This again points to the probability of an odour, although this is contradicted by my experiment with the naphthaline.

My coc.o.o.ns were all hatched, and the problem was still obscure. Should I begin all over again in the fourth year? I did not do so, for the reason that it is difficult to observe a nocturnal b.u.t.terfly if one wishes to follow it in all its intimate actions. The lover needs no light to attain his ends; but my imperfect human vision cannot penetrate the darkness. I should require a candle at least, and a candle would be constantly extinguished by the revolving swarm. A lantern would obviate these eclipses, but its doubtful light, interspersed with heavy shadows, by no means commends it to the scruples of an observer, who must see, and see well.

Moreover, the light of a lamp diverts the b.u.t.terflies from their object, distracts them from their affairs, and seriously compromises the success of the observer. The moment they enter, they rush frantically at the flame, singe their down, and thereupon, terrified by the heat, are of no profit to the observer. If, instead of being roasted, they are held at a distance by an envelope of gla.s.s, they press as closely as they can to the flame, and remain motionless, hypnotised.

[Ill.u.s.tration: THE GREAT PEAc.o.c.k MOTH. THE PILGRIMS DIVERTED BY THE LIGHT OF A LAMP.]

One night, the female being in the dining-room, on the table, facing the open window, a petroleum lamp, furnished with a large reflector in opaline gla.s.s, was hanging from the ceiling. The arrivals alighted on the dome of the wire-gauze cover, crowding eagerly about the prisoner; others, saluting her in pa.s.sing, flew to the lamp, circled round it a few times, and then, fascinated by the luminous splendour radiating from the opal cone of light, clung there motionless under the reflector. Already the children were raising their hands to seize them.

"Leave them," I said, "leave them. Let us be hospitable: do not disturb the pilgrims who have come to the tabernacle of the light."

During the whole evening not one of them moved. Next day they were still there. The intoxication of the light had made them forget the intoxication of love.

With creatures so madly in love with the light precise and prolonged experimentation is impracticable the moment the observer requires artificial light. I renounced the Great Peac.o.c.k and its nocturnal habits. I required a b.u.t.terfly with different habits; equally notable as a lover, but seeking out the beloved by day.

Before going on to speak of my experiments with a subject fulfilling these conditions, let me break the chronological order of my record in order to say a few words concerning another insect, which appeared after I had completed these inquiries. I refer to the Lesser Peac.o.c.k (_Attacus pavonia minor_, Lin.).

Some one brought me, from what locality I do not know, a superb coc.o.o.n enveloped in an ample wrapping of white silk. From this covering, which lay in large irregular folds, the chrysalis was easily detached; in shape like that of the Great Peac.o.c.k, but considerably less in size. The anterior extremity, which is defended by an arrangement of fine twigs, converging, and free at the converging ends, forming a device not unlike an eel-pot, which presents access to the chrysalis while allowing the b.u.t.terfly to emerge without breaking the defence, indicated a relative of the great nocturnal b.u.t.terfly; the silk-work denoted a spinning caterpillar.

Towards the end of March this curious coc.o.o.n yielded up a female of the Lesser Peac.o.c.k, which was immediately sequestered under a wire-gauze cover in my study. I opened the window to allow news of the event to reach the surrounding country, and left it open so that such visitors as presented themselves should find free access to the cage. The captive clung to the wire gauze and did not move for a week.

She was a superb creature, this prisoner of mine, with her suit of brown velvet, crossed by undulating lines. The neck was surrounded by white fur; there was a carmine spot at the extremity of the upper wings, and four great eyes in which were grouped, in concentric crescents, black, white, red, and yellow ochre: almost the colouring of the Great Peac.o.c.k, but more vivid. Three or four times in my life I had encountered this b.u.t.terfly, so remarkable for its size and its costume. The coc.o.o.n I had recently seen for the first time; the male I had never seen. I only knew that, according to the books, it was half the size of the female, and less vividly coloured, with orange-yellow on the lower wings.

Would he appear, the elegant unknown, with waving plumes; the b.u.t.terfly I had never yet seen, so rare does the Lesser Peac.o.c.k seem to be in our country? Would he, in some distant hedge, receive warning of the bride who waited on my study table? I dared to hope it, and I was right. He arrived even sooner than I had hoped.

Noon struck as we were sitting down to table, when little Paul, delayed by his absorption in the expected event, suddenly ran to rejoin us, his cheeks glowing. Between his fingers we saw the fluttering wings of a handsome b.u.t.terfly, caught but a moment before, while it was hovering in front of my study. He showed it me, questioning me with his eyes.

"Aha!" I cried, "this is precisely the pilgrim we are waiting for. Fold your napkin and come and see what happens. We will dine later."

Dinner was forgotten before the marvels that came to pa.s.s. With inconceivable punctuality the b.u.t.terflies hastened to meet the magical call of the captive. With tortuous flight they arrived one by one. All came from the north. This detail is significant. A week earlier there had been a savage return of the winter. The _bise_ blew tempestuously, killing the early almond blossom. It was one of those ferocious storms which in the South commonly serve as a prelude to the spring. But the temperature had now suddenly softened, although the wind still blew from the north.

Now on this first occasion all the b.u.t.terflies hastening to the prisoner entered the garden from the north. They followed the direction of the wind; not one flew against it. If their guide was a sense of smell like ours, if they were guided by fragrant atoms suspended in the air, they should have arrived in the opposite direction. Coming from the south, we might believe them to be warned by effluvia carried on the wind; coming from the north in time of _mistral_, that resistless sweeper of earth and air, how can we suppose that they had perceived, at a remote distance, what we will call an odour? The idea of a flow of odoriferous atoms in a direction contrary to that of the aerial torrent seems to me inadmissible.

For two hours, under a radiant sun, the visitors came and went before the outer wall of the study. Most of them sought for a long time, exploring the wall, flying on a level with the ground. To see them thus hesitating you would say that they were puzzled to find the exact position of the lure which called them. Although they had come from such a distance without a mistake, they seemed imperfectly informed once they were on the spot. Nevertheless, sooner or later they entered the room and saluted the captive, without showing any great ardour. At two o'clock all was over. Ten b.u.t.terflies had arrived.

During the whole week, and always about noon, at the hour of the brightest sunlight, the b.u.t.terflies arrived, but in decreasing numbers.

The total approached forty. I thought it useless to repeat experiments which would add nothing to what I had already learned. I will confine myself to stating two facts. In the first place, the Lesser Peac.o.c.k is diurnal; that is to say, it celebrates its mating under the dazzling brilliance of noon. It needs the full force of the sunlight. The Great Peac.o.c.k, on the contrary, which it so closely resembles both in its adult form and the work of its caterpillar, requires the darkness of the first hours of the night. Who can explain this strange contrast in habits?

In the second place, a powerful current of air, sweeping away in a contrary direction all particles that might inform the sense of smell, does not prevent the b.u.t.terflies from arriving from a direction opposite to that taken by the effluvial stream, as we understand such matters.

To continue: I needed a diurnal moth or b.u.t.terfly: not the Lesser Peac.o.c.k, which came too late, when I had nothing to ask of it, but another, no matter what, provided it was a prompt guest at the wedding feast. Was I to find such an insect?