The Courtship of Animals

by W. P. Pycraft

Photo by Paul H. Fabre.

THE FEMALE MANTIS DEVOURING HER MATE.

With these insects, as with the spiders and scorpions, the male is often eaten by the female.

Our survey of the “Arthropoda,” as those limb-bearing jointed animals invested in a horny, or, more exactly, a “chitinous” external skeleton are called has so far been confined to such as, during adult life, at least, are land-dwellers. But the aquatic types known as the “Crustacea” furnish some extremely interesting facts in regard to the problems of sex. In the first place, they too possess a stridulating apparatus. This is curious, but not surprising, because, although the skeleton of such creatures is of a harder and almost stone-like character, the development of roughened surfaces working in opposition to one another might well have been foretold to occur, at least in some individuals. Colonel Alcock—a naturalist who has contributed largely to our knowledge of marine animals by his researches in the Indian Ocean—in his most delightful book “A Naturalist in Indian Seas,” describes what he calls a “musical crab.” This is the great-horned Coromandel Strand Crab (Ocypoda macrocera). In both sexes of this remarkable genus he says, “the nippers, or chelipeds, are singularly unequal in size, and in all the species but one there is present on the inner surface of the ‘hand’ of the larger cheliped a transverse row of five teeth, which, when the cheliped is flexed, can be made to play against a ridge or another row of teeth on its ‘arm’ ... much as a man might rub one side of his chest with the palm of the corresponding hand. The whole mechanism, except that it is on a larger scale and has a more finished appearance, is very much like that by means of which crickets and grasshoppers produce their shrill music, and no one has ever doubted that it is used for the same purpose, though very few people have actually heard it in action. I myself ... was beginning to think that the structure must, after all, have some quite other function, when one morning ... on the sandy wastes of the Godavari delta, I at last, like Ancient Pistol, heard with ears that which I had been so long waiting for. That is to say, I heard a noise very much like that which an angry squirrel makes, and discovered that it came from a red ocypode crab into whose burrow another individual had trespassed.

“In order to understand the matter it should be known that these crabs ... are gregarious, and that each one has a burrow of its own. Though they may be seen marching in battalions across the sand, yet as a rule they stay close to their burrows, methodically searching and sifting the surrounding sand for any food that may have been thrown up by the tide, and flying to their burrows with headlong speed when alarmed. At first sight one does not understand the necessity for so much wariness, and for such a deep system of entrenchment, for the creatures seem to hold undisputed possession of the whole shore; but as a matter of fact they are preyed upon all day long by Brahminy kites, and when the jackals come out in the evening, by them. Now, although each crab may on ordinary peaceful occasions know its own home, yet when a crowd of them are running for their lives they may sometimes, one would think, act on the devil take the hindmost principle and try to squeeze into the nearest burrow. But as ancient philosophers do report, things may be done upon occasion which it is inexpedient to make a habit of doing, and this seems to be one of those things; for if many Crabs made a practice of crowding into one small burrow they would certainly run the risk of being suffocated, if not crushed to death outright. It seems probable, therefore, that it would be advantageous to the species as a whole if the rights of property in burrows were rigidly respected, and if each individual member possessed some means of giving notice that its burrow was occupied ... and I think that this consideration gives us a clue to the use of the stridulating mechanism. At any rate, I was often able, after my first accidental discovery, to elicit the sound, by catching one of these crabs and forcing it into a burrow which I knew was already occupied: the intruder would never go far in, but would crouch just inside the mouth of the burrow, and if it were made to travel deeper, then the voice of the rightful owner would be heard in indignant remonstrance from the depths.” Another species, the Grey Ocypode Crab (Ocypoda ceratophthalmus), possesses a similar instrument, and makes therewith a loud, croaking noise. But it does not often burrow deeply. Colonel Alcock therefore suggests that in this case it may be used for scaring enemies.

That these curious musical instruments may also be used in mate-hunting seems highly probable. If the stridulation is produced on one occasion to announce the fact that callers are not desired, it may on another signify an equally emphatic invitation to enter, the mood of the occupant being expressed by the character of the sounds emitted. It is significant, at any rate, that there are no external sexual differences in these species; hence the probability that it is by stridulation that the sexes distinguish one another.

This view seems to obtain confirmation from the fact that the Crabs of the genus Gelasimus, or “Fiddler-crabs,” which are near relations of the ocypode Crabs, and, like them, live in burrows in large companies, and are exposed to the same enemies, which they avoid in the same way by burrowing, have no stridulating mechanism, but the sexes are strikingly different. This is especially so in the case of the nippers, or chelipeds. These, in the female, are slender and much shorter than the legs, being used mainly for feeding. In the adult male one of these “hands” is often twice as big as the body itself! “Many uses,” remarks Colonel Alcock, “have been assigned to this enormous, lop-sided organ: some say that it is used as a stopper to barricade the mouth of the burrow, others that it is a sort of cradle or bridal-couch upon which the female reclines—the male, in this case, literally bestowing his hand upon the female; but from observations of Gelasimus annulipes, the species which most frequents the Godavari mud-flats, I believe that it primarily serves as a war-club, for the males indulge in interminable tournaments for the hand of the female; and secondarily, for it is of a most beautiful cherry-red colour, as an ornament to attract and delight the latter capricious sex.

“Landing one afternoon in March upon a cheerful mud-flat of the Godavari sea-face, I was bewildered by the sight of a multitude of small pink objects twinkling in the sun, and always, like will-o’-the-wisps, disappearing as I came near to them, but flashing brightly on ahead as far as the eye could reach. It was not until I stayed perfectly quiet that I discovered that these twinkling gems were the brandished nippers of a host of the males of Gelasimus annulipes. By long watching, I found out that the little creatures were waving their nippers with a purpose—the purpose apparently being to attract the attention of an occasional infrequent female, who, uncertain, coy, and hard to please, might be seen unconcernedly sifting the sand at the mouth of her burrow. If this demure little flirt happened to creep near the burrow of one of the males, then that favoured individual became frantic with excitement, dancing round his domain on tip-toe and waving his great cherry hand as if demented. Then, if another male, burning with jealousy, showed a desire to interfere, the two puny little suitors would make savage back-handed swipes at one another, wielding their cumbrous hands as if they had no weight at all. Unfortunately, though I spent many a precious hour on the watch from time to time, I could never see that these combats came to anything; the males seemed always to be in a state of passionate excitement, and the females to be always indifferent and unconcerned; and though the dismembered chelipeds of vanquished males could often be seen lying on the battle-field, I never had the satisfaction of beholding a good stand-up fight, fought out to the sweet end, or a female rewarding a successful champion with her heartless person.”

Photos by W. Saville-Kent.