Belt’s conclusions have been since amply verified, and the actual process of preparing the leaves and laying down the mushroom-beds, as well as the clipping and—if I mistake not—eating of the mushrooms, has been observed. Herr Möller—a German observer who resided for some years in tropical America—is usually referred to in this connection; but such extracts from his writings as I have come across are to me less convincing than the following account of Mr. Edward Tanner, which is contained in the Journal of the Trinidad Field Club.[[61]] The observations were made with ants in confinement, as were Herr Möller’s also, I believe. “Each forager,” says Mr. Tanner, “drops her portion of leaf in the nest, which is taken up as required by the small workers, and carried to a clear space in the nest to be cleaned. This is done with their mandibles, and if considered too large, it is cut into smaller pieces. It is then taken in hand by the larger workers, who lick it with their tongues. Then comes the most important part, which is almost always done by the larger workers, who manipulate it between their mandibles, the ant using her palpi, tongue, three of her legs, and her antennæ while doing so. It now becomes a small, almost black ball, varying in size from a mustard-seed to the finest dust-shot, according to the size of the piece of leaf that has been manipulated, which varies from ⅛ by ⅛ to ¼ by ¼ of an inch. These balls, really pulp, are then built on to an edge of the fungus-bed by the larger workers, and are slightly smoothed down as the work proceeds. The new surface is then planted by the smaller workers with slips of the fungus brought from the older part of the nest. Each plant is planted separately, and they know exactly how far apart the plants should be. It sometimes looks as if the plants had been put in too scantily in places, yet in about forty hours, if the humidity is regulated, it is all evenly covered with a mantle as if of very fine snow. It is this fungus they eat, and with small portions of it the workers feed the larvæ.”
The statement herein contained that the ants plant the new portion of their mushroom-bed with slips or plants taken from the already growing fungus is, as far as I know, new. I do not remember it in Herr Möller’s paper,[[62]] who speaks of the hyphæ of the fungus growing through and round the little leaf-balls within a few hours, but without reference to their being planted, nor is it alluded to by Professor Wheeler, who has studied the mushroom-growing ant—whether the same or a similar species I know not—in Texas. Forel, again, speaking of an allied form in Colombia, says, “The largest workers triturate the leaves”; and again, “the medium-sized workers of the minim caste are for ever clipping the threads of the fungus, which then develops the ‘Kohlrabi’ (the little round swellings, that is to say), on which the ants feed.”[[62]] Possibly this last may allude to the planting, but if so, it is the reverse of clearly put. Professor Wheeler also alludes to this constant clipping of the fungus, and sees in it the probable cause of the mutilation of the antennæ of the little blind cockroaches that live with these ants and take toll of their mushrooms.[[63]] But as these constitute the sole food of their insect cultivators, it is natural that the latter should frequently clip in order to eat them, and the clipping would, no doubt, stimulate their growth. All this, however, is different from the actual deliberate planting of the fungus on newly laid-down portions of the bed—an act which would imply a very clear intention, and make the ants farmers in the same way that we are. This, however, need not be the case if they only lay down the beds, for these at one time probably constituted their actual food, the crop of fungus being merely incidental. But if the ants deliberately plant the fungus, then, indeed, they must know precisely, in a human way, what they are about.
As we have seen, the leaves, from which, in their state of pulp, the mushrooms spring, are stored up by the ants in large underground chambers; but these mushroom-beds, or gardens, as they are often called, are themselves a sort of nest, containing tunnels and chambers, and not merely unformed heaps. It is in one or other of these chambers that the queen ant of the nest resides, a majestic creature, almost an inch long, but inflated both with pride and eggs to a disproportionate extent. Her sons and virgin daughters, who will some day be queens themselves, keep her company, whilst all about in the galleries and all over the broad, flat surface of the garden, which resembles a large flattened sponge, walk the different castes of workers, some large, some small, some medium-sized, with a few big-headed soldiers here and there amongst them, as though to keep the crowd in order. Whether they have really any such duty assigned them we do not know, but they do not appear to do any work, whilst the others are all busy at something, and the smaller workers particularly keep threading the stalks and filaments of the fungus in order to weed out any extraneous useless growth from amongst it.[[63]]
It is a sad reflection—thus sighs Professor Wheeler—that so much ordered energy, such apparent intelligence, should all be really due to—what he does not seem to be quite certain about, not automatism entirely perhaps, but if not, then semi- or demi-semi-automatism, tempered with “psychic plasticity.” Against this view of the matter we have that of Belt, who, after giving two instances, which came under his own observation, of intelligent adaptation, on the part of ants, to meet particular circumstances, exclaims, “Can it be contended that such insects are not able to determine by reasoning powers which is the best way of doing a thing, or that their actions are not guided by thought and reflection?”[[64]] But then Belt was not provided with the term “psychic plasticity,” and without it he could only infer intelligence from any intelligent act.
Still it cannot be denied that a great many instances have been given—noticeably in the case of “our ants” by Sir John Lubbock[[65]]—in which these paragons of insects have behaved very stupidly, or shall we say—for why should a creature that cannot be intelligent be stupid either?—with great “psychic rigidity”? Certainly such contradictions are very puzzling, but I would suggest one way of trying to estimate better the rigid type of ant intellect, which I believe to be absolutely new, and that is to compare it not with one’s own brain—or Darwin’s—but with that of a rigid type of person. It is wonderful what a difference this might make in our conclusions. An ant, for instance, that is unable, under some special circumstances, to get a thing down into its nest, because it persists in holding or pulling it, in the way it has always been accustomed to, or another that would rather be blown into the water along a known road than leave it for a new one, makes a poor figure in presence of the seven sages, or amidst a circle of senior wranglers mentally called up for its confusion; but we should think, rather, of some pin-headed servant-maid, setting an article of furniture each morning in the place that, with evident intention, you have removed it from overnight, or making up a larger and larger fire as the weather gets warmer and warmer. One should think of the obstinacy with which many people cling to old habits which changed times have made useless, or even harmful, and of how numbers not only prefer inferior things they are used to, to the most decisive improvements, but hate and revile such improvements as though they were undeniable evils. Instances will occur to everyone. I would rather not mention any for fear of alienating nine out of every ten of my readers. We should think, also, of savages or primitive, slow-moving peoples. What a great unadaptability, for instance, did the Matabele show in their methods of encountering our countrymen during the war, and throughout the rising; as also in that rising itself, since it was against all those well-known blessings which our empire confers upon savages.[[66]] It is to these less exalted levels of human faculty that we should look when we seek to compare an ant’s mind—when out of its usual set track—with our own, if we wish to do the ant any justice. That we pursue an opposite plan is my own explanation of many a partial verdict. To every experimenter in these directions (who should happen to ask my advice) I would say, first, “Do you know, or have you ever known, a really silly person?” and on his beginning, at once, with “Yes, Mrs.” or “Miss” (as the case may be), I would strike in peremptorily thus: “Then keep her—not Newton—in your mind as a standard of comparison.”
That ants should intentionally cultivate mushrooms will appear wonderful to everybody, and some will see in it the high-water mark of their mental development, by whatever path it has been arrived at. It seems natural to connect such doings with the fact that “in ants the cerebral ganglia are of extraordinary dimensions, and in all the Hymenoptera these ganglia are many times larger than in the less intelligent orders, such as beetles.”[[67]] Yet the brain of an ant—“one of the most marvellous atoms of matter in the world, perhaps more so than the brain of a man”—is “not so large as the quarter of a small pin’s head.”[[67]] Of what size, then, can a beetle’s be?—especially that family of beetles which grow and cultivate mushrooms, just in the same way that ants do. It would be suggestive—though I hardly know of what—should it be found that, comparatively speaking, they have no brain at all.
The beetles alluded to have been named, with reference to the particular kind of mushrooms they grow, ambrosia beetles, though in what the great superiority of these over those raised by the ants lies I do not know, for no one appears to have tasted them. It has been agreed, however, to call them ambrosia. “One of the most remarkable facts,” says Mr. Froggatt, “is that each group of these beetles is associated with a certain kind of ambrosia or fungus, notwithstanding that they are found in different timbers. This substance is actually cultivated by the mother beetle upon a carefully prepared layer or bed of wood-débris, generally at the end of the gallery; but in others the ambrosia is grown only in certain brood chambers of peculiar construction, whilst in others again it is propagated in beds near the cradles of the larvæ!”[[68]] When the latter hatch, they find a supply of celestial food awaiting them, and can walk about the various galleries, feeding upon it to their hearts’ content.
In other cases, however—that is to say, with other species—social development has gone further, and, besides boring galleries, the mother-beetle excavates a number of cells in their walls, like rows of bedrooms opening out of either side of a passage. She does not, however, quite finish her bedrooms, but, whilst they are still incomplete, lays an egg in each, and when this hatches, the young beetle, then in its larval state, takes up the task where she left off, and in time completes it. All the while they are growing up the mother feeds the young ones, and, between the intervals of doing so, stops up the entrance to the cell with a “plug”—such is the word employed; “to what base uses we may return, Horatio!”—of ambrosia. In time, when they have acquired the full imago form, each female beetle flies away to make a burrow and rear a family of her own, and in some species she is accompanied in this marriage flight, as it may be called, by the male. In others, however, the males are wingless, and remain in the burrow, till, when their appointed time comes, they die. Whether the male, when winged, assists the female in her mining operations I am not quite sure, inasmuch as that point seems to be avoided in the accounts which I have been able to consult, but the wingless male would not be able to do so, as he would be left behind in the burrow when the female flew away to found another colony.
The fungus, when it has once commenced to grow, increases very rapidly, so that if the number of beetles in the nest is much diminished, as, say, by some accident, the rest cannot eat enough to keep it down, and so, it would appear, are suffocated. It is asserted, however, that when the wingless males are deserted by the females, and would otherwise perish in this way, they all collect together in a few of the galleries and feast on the ambrosia there growing. By this means, we are told, they “prolong for a time their useless existence”—an ungrateful way of putting it, so it seems to me, as the poor things have already been useful in a very indispensable manner, so that their existence as a whole is anything but useless, and to separate a part of it from the rest and carp at that is silly as well as ill-natured. But it is the fashion to speak in this harsh way of the male insect, beginning with the drone bee; whereas when the female has done all that she can do—which is often just to lay her eggs—nobody talks of her useless existence. Fashion is a curious thing, and ants, even if they be automatons, are not the only creatures that do things automatically.
It is certainly very curious, if it be true, that the wingless male beetles should, by thus congregating together in this way, and so saving their lives, show more intelligence than the winged females, who, under similar circumstances, are choked with their ambrosia, as the Duke of Clarence was with his nectar in a malmsey-butt. It is true that with the males the thing happens every year, whereas with the females it is only accidental; but, in the particular circumstances, it is difficult to see how inheritance can have had anything to do with it. Here, then, are a particular family of beetles who live the same sort of social life that ants and bees do, which discovery appears to have been made by a Mr. Hubbard not so many years ago, and from whose paper on the subject all the above particulars have been taken, though only through the medium of various magazines, since even at the British Museum I was unable to get the paper itself. So long ago, however, as 1844 a certain Herr Theo Hartig “published an article on the ambrosia of Xyleborno (Bostrichus) dispar, in which he showed that it was a fungus growth (pilzrasen), and he named the fungus Monilia candida.” This statement is made by Mr. Hubbard in his much more recent account. Not feeling perfectly certain from it whether the origin, as well as the nature, of the strange-named substance was not also divined by the German investigator, I quote the reference in order not to do him a possible injustice, for to me it seems that there have been few more interesting discoveries than this of these ant-like, ambrosia-growing beetles. But why the ants only grow mushrooms, thus allowing themselves to be enormously outdone by an inferior insect, is more than I can understand.