And now a word of justice to these beetles. It might be supposed that, by burrowing into trees, they caused the death of the latter, but this is not really the case. Writing in The Agricultural Gazette of New South Wales for August, 1900, Mr. Froggatt, the Government Entomologist, makes the following statement absolving Xleborus: “This curious little beetle (X. solidus) is rather plentiful about Sydney, and is frequently sent to us taken out of the trunks of fruit trees, which it is supposed to have killed; but in all cases that have come under my notice it has had nothing to do with the tree dying, but is attracted to the tree as soon as it becomes sick, the bark begins to wither, and the first symptoms of decay set in.” Mr. Froggatt adds: “The instinct that leads these and other wood-boring beetles to a tree as soon as it is sick is something marvellous; in the tropics I have collected many fine, rare species upon the freshly cut tent-poles in our camp, attracted to the wood, but otherwise seldom found in the bush.” This instinct would seem to be a remarkably developed scent, though why a severed branch should smell differently from the tree of which it but a moment before made a part it is not easy to imagine. However, we cannot, without evidence, attribute clairvoyance to beetles, and perhaps it is the cut from which the scent emanates.
Another example of an insect which is neither an ant, bee, wasp, nor white ant, but which yet may be said to live a true social life, is the little creature which, under the name of Psocus venosus and as belonging to the order Carrodentia, will be familiar to everyone. It is nearly related to the so-called book-lice, but lives in the open air, “being seen,” says Mr. Leland Howard, “upon the trunks of trees, in flocks numbering from twelve to forty or fifty individuals.”[[69]] These browse together like a herd of miniature cattle on the various lichens that embrace the bark, and these they nibble so closely that wherever they move they leave a bare track behind them. Sometimes one family and sometimes several are included in the herd, all ages and stages being represented, from the wingless but free-moving larvæ to the winged imago form. The latter, however, though they be thus provided, will not readily forsake their young, but the whole of them, when alarmed, first run all together, and then, if the cause of disquietude continue, suddenly scatter as though in panic, and run hither and thither, in all and every direction. When the danger seems over, they close up their ranks again, and go on browsing as before.
The female Psocus lays her eggs in little clusters of from fifteen to twenty, and protects each cluster under a sort of dome or shield of gnawed wood which she presses upon them so that they stick to it. She is said to brood over the eggs, but this does not appear to mean that she actually incubates them. Rather, she remains about, keeping watchful guard till they are hatched, and then takes the young to find pasture, walking at their head like a hen in front of her chickens. From such beginnings as these it seems possible that the social life of ants has been, in the course of ages, evolved and developed.
CHAPTER XVI
From wood to ambrosia—Wood-boring beetles—Rival claimants—Stag and other beetles—Metempsychosis—Flies with horns—Comical combatants—Female encouragement—The sacred Scarabæus—A beetle with a profession—Table companions—Old and new fallacies—From theft to partnership.
IT is, no doubt, through feeding on wood that the beetles we have been considering came in time to feed on ambrosia. The particular fungus, that is to say, which for some unaccountable reason has received this name, appeared as a natural growth upon the walls of their tunnels, and in time it came to be thought necessary, and its coming was arranged for. By similar steps, probably, the leaves once carried as food to their nests by the sauba ants, or cooshies, have become the soil merely on which that food is grown; and so I have no doubt myself that even if the present agricultural ants of Texas do not purposely sow and afterwards reap the rice that springs up around the circular mound of their domicile, their descendants will do so. Indeed, it seems rather curious that, with such facilities for a gradual development, the habit has not yet been acquired; and this is the chief reason which inclines me to suspend judgment on the question, and wait for further observations. Far from thinking the thing too wonderful, I wonder if it be not the case. Such wonder, however, is for ants and not for beetles, except, indeed, ambrosia beetles, who certainly merit it, though in an opposite way. No other wood-borers of the order are anything but wood-eaters, or, at any rate, if a few feed on fungus, as would not be improbable, should it happen to appear, they have nothing to do with the cultivation of it. The words “as far as we know,” however, must be added to the foregoing statement. Numbers of beetles pass the larval and pupal stage of their existence within the trunk of a decaying or even of a perfectly sound tree, from which they issue after the final metamorphosis has been made. Amongst these is our own stag-beetle, in whom, that is to say in whose caterpillar, some suppose themselves to see the Cossus of the ancient Romans, which was as much appreciated by them, and, no doubt, justly, as are earthworms by the Chinese. Others, however, believe this to have been the large red meaty-looking caterpillar of the goat-moth; and as the one conjecture is quite as plausible as the other, the only, or, at any rate, the best way of arriving at a conclusion would be to try them both—a simple plan which, as far as I know, has not yet been adopted.
The stag-beetle—when of maximum size, that is to say, for it varies amazingly in this respect—is much the largest beetle which this our island possesses, but though, with its huge, antler-like jaws, it makes a good perennial illustration for all books of popular entomology, its merits seem to end there, for either there is nothing or nothing has yet been observed particularly interesting about it. No doubt, if we look at the matter from an absolute rather than a relative point of view, the second of these two explanations is the correct one, for a creature has only to be studied in order to become interesting; but as compared with ants, bees, wasps, and many other insects, beetles, or, at any rate, the vast majority of them, are not so very entertaining in their habits, and the stag-beetle has no superiority in this respect to correspond with its size and uncommon appearance. This appearance, however, is confined to the male, who alone possesses the great branching mandibles on which its greater size also is largely dependent. It would be natural to suppose that these formidable weapons, as they certainly appear, stood in relation to the combats of the males for the possession of the females, yet it is often stated that the short, sharp pincers of the latter, which can be made, it would seem—anyone who doubts may try—to meet in the flesh, are really the more efficient of the two. Be this as it may, it is not improbable that the stag-beetle’s jaws, since they are very handsome, may have been developed less as weapons than as ornaments, under the laws of sexual selection. Darwin, if I remember, was doubtfully of this opinion, and he attributes many strange projections and processes on the head or thorax of other beetles—as notably that huge one with a snout like a weaver’s beam, called the Hercules beetle—to the same agency. No use for this extraordinary trunk, as one may term it, has as yet been discovered, but as the under portion is covered with a thick matting of soft brown hairs, it would seem as though it had some office to perform, unless indeed we suppose this chevelure to be likewise admired. A lesser, though still tremendous, projection, starting from the head, as the other one does from the thorax, is likewise unaccounted for, for though the two together make in appearance a pair of uncouth and irregular pincers, they neither are, nor apparently can be used in this way. Nothing appears to be known of this strange creature’s habits, and the same may be said in regard to most of the more remarkable-looking beetles of the world, as well as those which are not so extraordinary in their appearance. The ways of beetles, in fact, have been but little studied, and it is perhaps not too much to say that if for every thousand that fill the show-cases in museums we could know the life-history of one, we might with infinite advantage, in exchange for this knowledge, throw the whole pin-forest of them into the sea. In what light this fact, if true, exhibits the labours of those naturalists—as the world calls them—who, living for years amidst the life-teeming regions of the earth, have spent their whole time in constantly killing and killing, coming home, at last, with an acre of carcasses, to write a book containing hardly anything of first-hand observation—the soul of natural history—I will not pause to inquire.