The Courtship of Animals

by W. P. Pycraft

CHAPTER XI
BEETLES THAT “BLUFF”

The Coloration, and other Forms of Ornament in Beetles, and the Significance thereof in regard to the Sexual Selection Theory—The Courtship of Grasshoppers and their Kin—The Remarkable Ears of Locusts and Grasshoppers—The Field-cricket and the Katydid as Troubadours—The Wonderful Performances of the Cicadas—The Duels of Long-horned Locusts—Dragon-flies—The May-flies’ “Dance of Death”—The Jaws of the Giant Alder-fly and their Strange Use—Some Curious Facts about Stone-flies.

In these pages it is contended that neither brilliant coloration nor any other form of ornamentation is to be ascribed to the direct action of “Sexual Selection.” That is to say, such conspicuous features have not been dependent on the action of female choice for their survival and development, but are rather the “expression points” of the internal, inherent growth variations, which, not being inimical to the welfare of the species, have been free to pursue their development in any direction which apparent chance may dictate.

The Butterflies and Moths well illustrate this in regard to coloration, for scent, not colour, would seem to be their principal source of information as to the outer world. The Beetles are no less instructive; for these creatures, though they contain numerous highly-coloured and some exquisitely beautiful species, are more remarkable for their bizarre shapes, and it seems impossible to regard these as the products of sexual selection. Yet this is the interpretation of their origin which, in the judgment of Darwin, we must adopt. He evidently had misgivings as to the correctness of this view; but it must be remembered that in reviewing the facts relating to these lower orders of Creation he was biased by the evidence which he had brought together in regard to the behaviour of the higher groups under the stimulus of sexual emotion. Convinced that female choice obtained here, he was but following the logical result of such conclusions in postulating the same factor wherever it could conceivably be applied. The most formidable critic of the Darwinian theory of Sexual Selection was Darwin himself. The dominant ambition in all his work was to explain his facts, not to establish his theory; and he was convinced that his theory of Sexual Selection did achieve that end; though there were cases where the evidence he was analysing seemed less clear than in others. That the Beetles presented difficulties is evident from his comments thereon. He was puzzled by the vivid coloration which some species present. “They may serve,” he remarks, “as a warning or means of recognition ... as with Beetles the colours of the two sexes are generally alike, we have no evidence that they have been gained through sexual selection; but this is at least possible, for they may have been developed in one sex and then transferred to the other; and this view is even in some degree probable in those groups which possess other well-marked secondary sexual characters....

“Some Longicorns, especially certain Prionidæ, offer an exception to the rule that the sexes of Beetles do not differ in colour. Most of these insects are large and splendidly coloured. The males of the genus Pyrodes ... are generally redder but rather duller than the females, the latter being coloured of a more or less splendid golden-green. On the other hand, in one species the male is golden-green, the female being tinted with red and purple. In the genus Esmeralda the sexes differ so greatly in colour that they have been ranked as distinct species: in one species both are of a beautiful shining green, but the male has a red thorax. On the whole, as far as I could judge, the females of those Prionidæ in which the sexes differ are coloured more richly than the males, and this does not accord with the common rule in regard to colour when acquired through sexual selection.”

While there is nothing very remarkable in the two sexes being coloured alike, it is certainly strange to find the female more brilliantly coloured than the male. And this because among the higher vertebrates, as among the birds, the female exceeds in brilliance only where she also plays the rôle of wooer instead of wooed; leaving to the male the whole responsibility of rearing the family. With the Beetles the family has to rear itself, parental care being limited to the right disposal of the eggs. By some change in the character of the germ-plasm the females may have, in these cases, acquired more “maleness,” more of the qualities which are answerable for the secondary sexual characters of the male, or, what seems rather to be the case here, a result like that which has been reached in certain of the Pigeons and Parrots has been arrived at. That is to say, the tendency to intensification of pigment in the female struck out a new line, instead of following that of the male. This rather rare form of sexual dimorphism is also met with, it will be remembered, among the Butterflies and Moths.

While brilliant colour is the more usual form of ornament among the Beetles, there are many species wherein the males have developed enormous horns, or have greatly exaggerated the length of the jaws; and these outgrowths give the impression of a formidable armature, but so far as the evidence goes this is by no means the case. They must therefore be relegated to the category of “ornaments,” though the term “excrescences” would more fittingly apply to them, for they are “ornaments” only from a human standpoint. At any rate, there is no evidence whatever that they serve to enhance their possessors in the eyes of the females.

In relation to the Sexual Selection theory these excrescences are of quite exceptional interest, for they throw a strong light on the meaning of ornament, such as obtains among birds, which seem to show a consciousness of its existence and effectiveness. Darwin argued from the birds to the Beetles. Convinced that the gorgeous crests and trains and vivid colours were appreciated by the females of the former, he was impelled to believe that the ornaments of the latter had developed in like case by the fostering influences of the females. Similarly, from the evidence as to the use of horns in the case of mammals, and spurs in the case of birds, he was induced to believe that the horn-like outgrowths of Beetles had been attained by like influences. But in both kinds of cases, he could only infer their action, for he could discover no really decisive instances of conquest either by display or by battle, such as he was able to produce in the case of the higher animals. Had chance directed his attention in the beginning either to the Warblers among the birds, or the beetles among the insects, his interpretation of the action of sexual selection, it is more than probable, would have been materially different from that developed in the “Descent of Man.” No additions of any importance have been added to the facts he so laboriously collected.

As touching the “horns” it should be remarked that these may arise either from the head or from the thorax, or from both, and sometimes even from the under surface of the body.

One of the most remarkable instances of these singular outgrowths is that of the Hercules Beetle (Dynastes hercules) of the West Indies and tropical America. Herein the roof of the head is prolonged into a great upturned beam bearing tooth-like prominences, and the top of this is opposed to a still more massive beam, whose base covers the whole roof of the thorax, and whose tip extends far beyond that projecting from the head. A pair of “teeth” point downwards from the middle of this beam, whose under surface is thickly covered with short chestnut-coloured hairs forming a brush-like surface. In another, Copris isidis, the head bears two short, rhinoceros-like horns, and the thorax a short, triangular overhanging ledge: in Phanœus jaunus there is a single horn on the head, and the thorax bears two short, forwardly-projecting blades, one on each side; while in Onthophagus rangifer—the Reindeer Beetle—the head bears a pair of horns curiously like the antlers of a deer. One might cite many such instances, all varying in detail, but these will suffice.