The Courtship of Animals

by W. P. Pycraft

All the insects so far surveyed have been more or less conspicuous for their vivid hues, yet in none of these have elaborate “displays” been recorded. To find demonstrativeness of this kind one must turn apparently to a group of minute, lowly organized, dull-coloured, wingless insects with ugly misshapen heads and bodies. The sexes do not differ in appearance, but they are interesting on account of the sedulous court which the males pay to the females. The late Lord Avebury, in a Communication to the Linnean Society, remarked of them: “It is very amusing to see these little creatures (Smynthurus luteus) coquetting together. The male, which is much smaller than the female, runs round her, and they butt one another, standing face to face and moving backwards and forwards like two playful lambs. Then the female pretends to run away and the male runs after her. With a queer appearance of anger, he gets in front and stands facing her again; then she turns coyly round, but he, quicker and more active, scuttles round too, and seems to whip her with his antennæ; then for a bit they stand face to face, play with their antennas and seem to be all in all to one another.”

The Dragon-flies are among the most beautiful of insects; they are also relatively long-lived, and they are conspicuous. Yet this beauty must be attributed to some inherent inward grace rather than to the æsthetic instincts of the female. Moreover, in the matter of size and beauty there is little to choose between the sexes; where any difference occurs the males have the advantage. Though the mode of copulation is well known, nothing has been discovered as to the means whereby male and female discover one another. It is doubtful whether this can be done by sight, for with all the beauty of their shimmering suits of mail and gauzy wings, their vision is limited to a field of a few inches. Possibly scent is their guide; at any rate, dead Dragon-flies have a vile odour.

It is worth noting that there are no wingless Dragon-flies, and that none have developed unnecessary ornament in the form of spines, horns, or frills of any kind, such as are so commonly met with among groups of more sedentary habits like the Phasmidæ and the Beetles, for example. In other words, there is clearly a direct relation between ornament and the mode of life. It is also clear that some modes of subsistence are very inelastic, allowing of no more than very slight structural variations, for the Dragon-flies are an extremely ancient group. Fossil species of large size are known from the Lower Lias, and the remains of a giant measuring two feet in expanse of wings has been found in the Carboniferous. This species, however, seems to have stood near the parting of the ways between the May-flies and the Dragon-flies. But be this as it may, undoubtedly Dragon-flies hovered over the backs of sleeping Ichthyosaurs and furnished food for Pterodactyles millions of years ago, as they now hover over lazy kine for the sake of the flies forgathered there, or dodge to avoid the stoop of the Hobby, and in all this vast space of time they have not appreciably changed.

And what is true of the Dragon-fly is true also of the May-fly, for it is clear that they are of the same stock. It is true at any rate in so far as the conformation of the body is concerned. The possibility that it may be equally true in regard to the details of their life-history almost staggers one, because these are, in many respects, of a quite remarkable character. As with the Dragon-fly, there is a prolonged period of larval life, lasting from one to two years, which time is passed in streams and pools where a luxuriant vegetation ensures a plentiful supply of food. Some are carnivorous, but in the majority of species minute plants only are eaten. More than forty species are to be reckoned as natives of the British Islands, the commonest being the “Green Drake” and “Grey Drake,” beloved by the fisherman. These names are applied, it may be mentioned, to the phase known as the sub-imago which precedes the fully-adult stage, of Ephemera vulgata and E. danica.

Save that it is curious that while the larvæ of some species are carnivorous those of others are vegetarians, there is nothing very remarkable about what may be called the infantile period. But when this is ended the span of life remaining to them as adults is brief indeed. Instinctively realizing that the time of transfiguration is at hand, the erstwhile crawling grub rises to the surface of the stream, and almost in the twinkling of an eye it mounts into the air on gauzy wings, there for a brief space to execute an aerial dance which in its every phase is amazing. Some species never see the sun. They emerge as the sky begins to redden, and as its glory fades they, too, expire. This brief space is all that Nature has allowed them in which to fulfil her behest to all living things—to increase and multiply. And myriads die without even a chance to effect this consummation of existence.

The dance is a Dance of Death, and it is performed by a host so vast as to surpass the bounds of belief save to those who have had the good fortune to witness a scene so amazing.

D’Albertis tells of a gathering which he witnessed on the Fly River, New Guinea—for these insects have a world-wide distribution—wherein countless myriads were assembled. “For miles the surface of the river, from side to side, was white with them as they hung over it on gauzy wings; at certain moments, obeying some mysterious signal, they would rise in the air and then sink down anew like a fall of snow.” And in this assemblage he estimated that there was but one female to every five or six thousand males. It is during this flight that the act of mating is performed. The fortunate male from the host of rivals, in this mid-air embrace is aided by the foremost pair of legs, which are especially curved to effect this purpose. The embrace is momentary. Thereafter he dies; to the female a somewhat longer span of life remains, for she has yet to deposit her eggs, and this being done en masse, she, too, expires.

It is curious that these creatures, which in their winged state have never seen the sun, should be attracted by light. But such is the case. I well remember witnessing an instance of this years ago, while staying, one August, at Bingen on the Rhine. Dinner was served in the open air, and just as the soup was served May-flies in myriads swarmed round the lamps and fell on the tables as thick as snow-flakes. Some of these were in copula, and I succeeded in bottling a few specimens for the British Museum, where they still remain to remind me of this amazing scene.

About three hundred species of May-flies are known, and some enjoy a somewhat longer span of life than others. In no case, however, do they emerge till just before sunset; but in some species it is believed life may be prolonged for as much as three or four days, or even longer, if the weather be cold and wet, so as to keep them in a state of enforced rest, which amounts to a state of coma.

That their hold on life during this final stage of existence is brief there can be no gainsaying, for it is passed fasting. Jaws are wanting, and the whole alimentary canal has been transformed into one long air-chamber. Its walls are now of extreme tenuity, and by changes in the interior of the tube, valves are formed which convert the stomach into a capacious air-sac.” When movements,” remarks Dr. David Sharp, “tend to increase the capacity of the body cavity then air enters into the stomachic sac by the mouth orifice, but when muscular contractions result in pressure on the sac they close the orifices of its extremities by the valve-like structures just referred to; the result is, that as the complex movements of the body are made the stomach becomes more and more distended by air.” It was known even to the old naturalists that the dancing May-fly is a sort of balloon, but they were not acquainted with the exact mode of inflation. Palmen says that in addition to the valve-like arrangements we have described, the entry into the canal is controlled by a circular muscle with which are connected radiating muscles attached to the walls of the head. The canal thus strangely transformed performs the functions of a balloon, and at the same time aids the functions of the reproductive organs.