CHAPTER IV

Ant parasites—Fleet-footed brigands—Honey-stealing mites—A strange table companion—Privileged cockroaches—Ants and their riders—A fly-ride on beetle-back.

LEAVING the beetles—though as there are probably some thousands that live habitually in ants’ nests, we have said very little about them—we may glance at an extraordinary little creature, in appearance something like a wood-louse with a fish’s tail, that resides with certain ants on the footing of a freebooter, constantly stealing from them, and eluding their resentment by extreme activity, living, as it were, in a state of perpetual motion. The legs of these persistent yet withal timid brigands are many and long, which, together with their shape and general lightness of build, enables them to run with great speed, so that they easily outdistance the ants, and, escaping to some less frequented part of the nest, with which they are always well acquainted, remain there quiet for a time. Should a single ant approach them, however, they immediately run away, or, if forced by circumstances to be near one or more—which, in an ants’ nest, must be often difficult to avoid—make a point, apparently, of never keeping still, as though to confuse them, or, perhaps, to be the better able to dash off at any instant.

AN INSECT FREEBOOTER, AND AN INSECT BEGGAR.

The extraordinary looking insect shown towards the top is the lepismid, or fleet-foot, who lives by stealing food from ants when they are in the act of passing it from one to the other. The atemeles beetle shown below is begging food, which will not be refused, from the ant in front of him.

The way in which these fleet-foots secure their food is highly remarkable, each little theft—which has about it more of the parasite than the brigand—occasioning a group of three. The ants upon which they live are of the species known asLasius umbratus, and, like many other kinds, often feed one another, the hungry asking of the full, by whom he is rarely, if ever, denied. In the process of regurgitation—with which we are now familiar—the two stand fronting each other, with mandibles interlocked, and a drop of honey passes from mouth to mouth. For an instant it trembles between the two, resting on both, and that instant is the opportunity of theLepismid. Darting forward, he interposes his own, and having absorbed some portion of the dropin transitu, speeds swiftly away to make a third elsewhere. Such a life, however great may be the thief’s agility, is full of danger, and, from time to time, an individual is captured and killed. In nests under observation such executions may be witnessed, andLepismidcorpses—or, as various professors prefer calling them,cadavers—are sometimes noted. Under artificial conditions, however, opportunities of escape are much more limited, unless, indeed, some special provision is made. Thus, when Professor Wheeler first introduced a colony ofLasius umbratusinto one of hisformicariums, he found, after a couple ofdies,[12]fiveLepismid cadavers. But having, by the addition to the saidformicariumof arefugium, or asylum, made it more asin natura, this mortality ceased, and the remainingLepismidscontinued henceforthexistentes.

A similar mode of feeding, but under circumstances of much greater security, is indulged in byAntennophorus, another ant-guest, whose relations with its host are of a still closer description.Antennophorusis a mite which, according to M. Janet, fixes itself on to the head, or the sides of the abdomen, of the ant which it affects, and clings there as long as it sees fit. This it is enabled to do owing to a special adaptation of the feet, which end in little horny cups (corniculais the word here) furnished with some substance of so adhesive a quality that it might well be called “stickphast,” if no Latin word were at hand. Not all the feet, however, are of this description, for the anterior ones are transformed into a pair of long waving antennæ, which contain olfactory organs of the greatest sensibility. With these their owner makes up for the want of eyes, and, smelling and feeling its way, walks, when it wishes to, along the bodies of its hosts, passing from one to another. Sometimes, either by accident or otherwise, it becomes detached, and is then helpless as far as locomotion is concerned, but by no means so in other respects. Its object, now, is to reaffix itself: nor is it long before it succeeds in doing so. As it “lies upon the soil in one of the galleries of the nest it raises and stretches forward its first pair of ambulatory feet, and, at the same time, explores the space around it with its long antenniform ones. These appendages are much more agitated when an ant passesclose by. Should it pass near enough, theAcarid(which has a finer sound than ‘mite’) glues itself on to its body by means of the cup of sticky material at the end of one of its ambulatory feet, which it holds up ready for this operation, and it can, in this way, soon climb up and fix itself in a good position on its host. The latter is surprised, and seeks to rid itself of its strange companion, but failing in this, it becomes resigned very quickly (as we do to increased taxation) as soon as theAcaridhas taken up one of its normal positions.”[13]It will carry two indeed, or even three, without complaining. An ant with one of these burdens fixed, like the income-tax, to the under side of its head, and two others, which may stand for a rise in tea and sugar, is a very common sight.

The feeding ofAntennophorushas been closely observed by M. Janet in his artificial nests, and is thus described by him: “The ants had acquired a habit of placing themselves, crowded one against another, in one corner of the nest, and thither came such as had their crops well filled, after a meal of honey, and disgorged it before the mouths of their comrades who had none. While the fasting ant was eating the honey thus disgorged,Antennophorus, riding on its head, took its share. To do this, it pushed itself forward, and thrust its rostrum into the droplet, and generally, whilst holding itself in position by means of the two hinder pairs of legs, it attached itself by means of the forward pair (which in this case, however, would represent antennæ) to the head of the disgorging ant.”[13]Perhaps there is some little mistake here—possibly I have not copied the passage correctly. There has beenno hint before as to the modified antenniform legs of the parasite performing any other office than that of feeling and smelling, whilst the word “attach” or “affix” is that always used to describe the working of the sticky, cup-footed ones. In the position described the antennæ might very well act as supports, but hardly, one would think, in such a way as that their owner could be described as attaching himself through their means. Possibly it is the first pair of true legs that act in this way, but the matter is of no great consequence—not more than a war, say, or the fall of a ministry, in the general run of things. Suffice it that we have our picture, the little parasite stretched, like a bridge, between the heads of the feeding and disgorging ants, and taking its share with the latter.

Lasius somethingis the name of the ant whichAntennophorusutilises in this way, and it is, I think, a European species. Another one—Pachycondyla harpax—the large, black ant of America—wears its parasite round its neck, like an Elizabethan ruff. In this case both host and guest are in the larval state, and the involuntary partnership between them—involuntary probably on the part of either—is not dissolved until both have attained full maturity. The position of affairs is this: the ant larva apparently lies on its back upon earth a little hollowed, to receive it, by the workers of the nest. The parasitic larva—that of an unknown species of fly—has a long, slender neck, as we may call the anterior part of the body, and whilst this is wound about the corresponding portion of its host, the body, which broadens out afterthe manner of an oil-flask, is affixed by a disc at its end to some part of the back of the latter. When the ants feed the larvæ, they place the food—which consists either of grain that has been stored, or of insects captured and torn up by them—on the broad surface of the abdomen, which forms a sort of trough for its reception. Immediately upon feeling the welcome load, the hungry larva stretches down its head to the banquet, but that of the parasite moves with it, and its small, sharp jaws take eager toll of each dish. Thus the two feed together, cheek by jowl, and should what has been provided prove insufficient for this double onslaught, the unbidden guest will stretch its snake-like neck, and move it ceaselessly until the ever-ready jaws come into contact with a second feast, upon the table next it. Should none, however, be within reach, the guest will give vent to its irritated feelings by biting the bodies of such unbounteous Timons, or even that of its own host. They wriggle with pain, and this may possibly induce the ants to bring them fresh supplies, under the impression that they are hungry, as indeed they may be, with meals shared in this way. If so, we can hardly suppose a parasitic larva to act with such a motive, but as the best biters would in this case get the most food, natural selection may possibly have helped to develop the habit, which would have a compensating advantage for the wrigglers too. As the French say, “Il y a compensation en tout.”

The parasite, whilst stretching out as far as it can from the body of its host, in quest of food, remains, all the while, attached to the latter by the disc in which its bodyends. It can, however, leave one ant larva for another, though Professor Wheeler, to whom we owe this interesting discovery, believes that it does this “with great reluctance, and only under urgent circumstances, such as extreme hunger, the death of the larva to which it is attached, and perhaps, when fully mature, and about to pupate.”[14]So long, indeed, as its original host, on whose body, when quite young, it was probably hatched from the egg, continues well and is well fed, it has no reason to seek farther, since all its wants are provided for. It is not only fed by the worker ants, but shares in any other of the benefits which these may bestow upon the rising generation of the nest. Thus, if they move larvæ, as is customary, to give them change of temperature, and produce the requisite hygienic conditions, the parasite is moved along with them, and it is cleaned also—a still more important advantage possibly—at the same time as they are. At such times the ants never seem to notice the uncouth incubus upon the bodies of their infant sisters, though one would suppose the difficulty would be not to do so. They are, it is true, blind, or nearly so, but it seems strange that their sense of touch, which is no doubt delicate, should not be able to inform them, since the parasite, though small enough, absolutely, is of great size regarded as an excrescence on its host’s body. This probably is the way in which the matter presents itself to the ants, if they think about it at all, for since the two lives are passed constantly together, and are subjected to the same conditions, it is likely that they share one smell between them.

But this curious parasitic relation between ant and fly is not confined to the larval stage of each. Continued observation led to a further discovery which I give in Professor Wheeler’s own words: “As the days passed, the mature ant-larvæ spun their brown cocoons one by one, and one by one the mature commensals (the larval parasites, that is to say) disappeared. No traces of them could be discovered. The only remaining resource was to open the cocoons. Five were opened, and in two of recent formation commensals were found! Having shared the table of their host, they had come to share its bed as well. The dipteron (the parasite, as I have said, is a fly) had pupated after the manner of its kind, forming a puparium, that is, instead of spinning a cocoon like the ant larva: the dead larval skin, somewhat shrivelled and contracted, was used as an envelope, and within this the pupa proper was found. In all cases the puparium was located in the caudal pole (at the bottom) of the ant cocoon, and was immovably stuck to the wall of the cocoon, its anterior end directed towards the cephalic pole”[14](the top). But what, asks Professor Wheeler, does the commensal larva do “while the ant-larva is weaving its cocoon? Does it move about to avoid the swaying jaws of the spinning larva? or does it take up its position, from the first, at the posterior end of the larval ant, and there remain motionless while the posterior pole of the cocoon is being completed? It is very difficult to answer these questions.”[14]

One might think that young ants thus deprived, day by day, of a portion of every meal, would be stunted in theirgrowth, and not make such large and healthy workers as those who had never been encumbered with a parasite. This, however, does not seem to be the case, and no difference can be detected between the one and the other. Perhaps, therefore, ants habitually eat, if not more than is good for them, at least more than they require. This is the case almost universally amongst civilised men, at least in Northern Europe, and with savages to a still greater extent whenever the wherewithal is at hand. In the above case we have, as Professor Wheeler remarks, a very perfect example of what is termed commensalism, in the original meaning of the word—that is to say, of two or more individuals dining together at the same table. As applied to natural history, the individuals in question must be of different species, but it is not often that the definition otherwise is so rigorously adhered to.

This curious parasite inhabits the nests, or, more strictly speaking, the bodies, of an ant, native to Texas, that has long been famous as a storer of grain, but whose supposed still further achievements in an agricultural direction would now seem open to doubt. In the nest of another American ant, which most certainly does grow mushrooms, the same observer found another “myrmecophile,” or ants’ nest insect, viz. a minute species of cockroach that lives its life amongst the caves and galleries of the great vegetable mass which forms, and is designed to form, the mushroom bed, upon the product of which it feeds. Here again the ants have become thoroughly reconciled to the presence amongst them of a guest from which, as far as can be seen, they derive no benefit, whilst havingto submit to a loss, through its agency, of some part of the fruits of their labours. These little cockroaches are fairly numerous, and have become so adapted to living in darkness that their eyes have almost disappeared. Another loss, or partial loss, is of a more curious nature, and, one might think, would be a great privation to them. Their antennæ, namely, are always incomplete, but this does not seem to have come about by a gradual process of atrophy, but rather to have been caused by mutilation during their owners’ lifetime. But how has this happened, and what has been the mutilating agency? Professor Wheeler’s explanation, which he believes to be the only one, is that their antennæ have been unconsciously sheared off by the ants, whilst engaged either in clipping their mushrooms or in cutting up the pieces of leaves which they are continually bringing into the nest, to add to the bed on which they grow. “It is easy,” he says, “to understand how an insect like a cockroach, living in the midst of thousands of ants which are continually opening and closing their scissor-like mandibles, should be certain, sooner or later, to have its long antennæ cropped. One wonders how the tarsi (the legs, that is to say) of the cockroach escape the same treatment.”[15]This wonder, however, if there is really any reason for it, suggests a doubt as to the sufficiency of the explanation here offered. The antennæ, one would think, might be held high, in which case, if sheared at all, it could only be at the base, but if here (as would not, however, seem to be the case) why should not the legs be sheared too? Again, it seems possible that the insects themselves may be in the habit ofgnawing one another’s antennæ. As the cockroaches live and flourish it would seem that this mutilation of their antennæ, if that, indeed, be the explanation, can do them no great injury. Yet these organs are supposed to be of great importance to insects, and, judging by their length and delicacy, one would think that they were especially so to the members of the cockroach family. In this case they would probably be extremely careful of them, and the fact that these ants’-nest cockroaches do not seem to be so, may show that subterranean conditions, contrary to what one might have expected, have affected their efficacy.

A RIDE ON BEETLE-BACK, AND A LIVING SWEET-SHOP.

Enjoyment seems to be the only motive the fly has for riding on the back of the African beetle shown in the upper part of this illustration. Beneath is shown the well named honey-pot ant with its distended body full of honey, which it gives away to any hungry working ant.

A diet of mushrooms, or fungus, is not the only thing for which these little blind, light-shunning cockroaches are indebted to their landlords, the ants, for often one of them may be seen to mount upon one of the latter, and take a ride on its back. They seem especially fond of the soldiers, as horses, and will sit perched on their enormous heads, as they walk up and down in a stately sort of way, sometimes for quite a long time. Enjoyment seems here to be the only motive, and perhaps it is a natural one, since there is a fly in Africa which seems to have quite a passion for riding on the back of a beetle. “Across the mouth of the Seyhouse,” says the Rev. Mr. Eaton, “on sandy pasture-land bordering the seashore, bigcoprophagousbeetles—it sounds abusive, but no harm is meant—are common, sheltering in large holes in the soil, when at rest, and running about on business. A small species ofBorborinæ(that is the fly) may often be seen riding on their backs, chiefly on the pronotum and about the bases of the elytra, sometimes half a dozen females on one beetle. The beetles occasionally throw themselves on their backs, and try to get rid of them by rolling; but the flies elude all their efforts to dislodge them, dodging out of harm’s way into the jointures of the thorax, and darting from back to breast, and back again, in a way that drives the beetle nearly mad. In vain she scrapes over them with her legs, in vain does she roll over, or delve down amongst the roots of the herbage: the flies are as active as monkeys (not perhaps a very striking simile here), and there is no shaking them off. It is difficult (such is their strange predilection) to get them off into the killing-bottle. Nothing (not even the killing-bottle) persuades them to fly, and they would very much rather stick to the beetle than——” what? Not go to heaven, but “be driven off it down the tube.”[16]The tube must be the neck of that same bottle. This, surely, is a case of infatuation if ever there was one. Eccentric fly! And what must be the charms of a beetle that can prevail over those of cyanide of potassium! But the beetle, it must be remembered, is acoprophagousone. There may be a world of explanation in a word like that.

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