CHAPTER XII
Ants and their honey-cows—A mutual benefit—Unity of motive—The end and the means—Two ways of getting honey—Insect cattle—Wasps as cow-milkers—A cow-keeping bee—Ant cow-sheds—Aphides in ants’ nests—Children of light and darkness—Forethought extraordinary.
A drop of honey, or something like it, is the connecting bond between the ant and the Aphis. It is exuded by the latter through certain tubercles which are situated at the end of the abdomen, and is, of course, the product of the endless quantities of sap, which, so long as it lasts, these insects are for ever pumping up from the plant they inhabit, and swallowing. This honey, or honey-dew, to use the more special name bestowed on it, the ants want, but they are not content with drinking it whenever it issues from its manufacturers, in natural course. This is not sufficient, and they have learned to increase the flow of so valued a beverage by their own efforts—in other words, they milk the Aphides, which thus become their cows. To do this they tap them with their antennæ, softly and gently, on the sides of the abdomen—a quick little shower of touches. Under the influence of this probably pleasant sensation the Aphis becomes willing to part, and, raising the abdomen, “teems her refreshing dew” in a drop from the tip of it. This action of the ants cannot, in Europe, be successfullyimitated, at least it has not been, and if an ant is not forthcoming the fluid is contained in the body of the Aphis until necessity compels its being ejected. Probably the ants, if delayed in their visits, are missed by the Aphides, as a cow misses her milker, and long before they do excrete, as the process is called, they would perhaps have done so had they felt able. The sensation no doubt of the ant’s antennæ on the abdomen has become, through usage, the almost necessary stimulus to the act produced by it.
The above remarks are best illustrated by a quotation from Darwin, which, in my opinion, should always be given in any general account of the relations of ants and Aphides. “I removed,” says Darwin, “all the ants from a group of about a dozen Aphides on a dock plant, and prevented their attendance during several hours. After this interval I felt sure that the Aphides would want to excrete. I watched them for some time through a lens, but not one excreted. I then tickled and stroked them with a hair in the same manner, as well as I could, as the ants do with their antennæ; but not one excreted. Afterwards I allowed an ant to visit them, and it immediately seemed, by its eager way of running about, to be well aware what a rich flock it had discovered; it then began to play with its antennæ on the abdomen first of one Aphis and then of another; and each, as soon as it felt the antennæ, lifted up its abdomen and excreted a limpid drop of sweet juice, which was eagerly devoured by the ant. Even the quite young Aphides behaved in this manner, showing that the action was instinctive, andnot the result of experience. It is certain, from the observations of Huber, that the Aphides show no dislike to the ants: if the latter be not present, they are at last compelled to eject their excretion. But, as the excretion is extremely viscid it is no doubt a convenience to the Aphides to have it removed; therefore, probably, they do not excrete solely for the good of the ants.”[45]
If the reverse of this were the case, if the Aphides did excrete for the sole benefit of the ants, then, in Darwin’s own opinion, the case for natural selection would be broken down, and with this there would be some better ground of reason for those who would see in relations of this sort a set-off, as it were, against the never-ending bloodshed and rapine, accompanied with suffering in varied—often in an intense—degree, which is the very stuff out of which Nature has woven her mantle. But there can be no essential difference where the principle at work is precisely the same. So long as a creature does benefit itself, the way in which it does it, and the incidental effects of its doing so, are of no consequence; it is the motive power that the philosopher has to consider, and there is little comfort—if comfort be needed—in knowing that an animal, to do itself good, is doing good to some other, when one also knows that, governed by the same incentive, it would as cheerfully prey upon that other’s eye. As Hamlet says, in such a case “the readiness is all.”
As an illustration of this truth here is another picture of how ants procure honey from a weaker creature that may happen to have swallowed it, when it is not to be obtained by the soft methods of persuasion. “Once upona time,” says Dr. Lincecum, “there dwelt in my yard a flourishing colony of the very smallest species of black ant,” and having described how these Lilliputians found and ate some syrup belonging to the household, and were in consequence attacked by a larger and stronger species, he continues, “They”—that is the attacking party—“grabbed up the heavily burdened little fellows, doubled them, and biting open the abdomen, drew out the full sac, and seemed to swallow it. Then, casting the lacerated carcase aside, they furiously sprung upon another of the panic-stricken crowd and repeated the horrid operation.”[46]Clearly, then, Nature, so long as she can attain her end, cares not by what means she attains it.
Independently of any feeling of comfort which the Aphides may experience in being milked by the ants, observation at once shows that they benefit largely, in a general way, by the attentions of the latter. It is not enough for the ants to milk their cows when they happen to meet them. They go very much farther than this, and cow-keeping is of as much importance with them as with us. Lucky the Aphis who has a guard of ants round it, fiery warriors prepared to defend their property against all foes. None need be feared now. Let but an Ichneumon buzz, and a dozen stalwarts start to the rescue.
“I dare thee but to breathe upon my love.”“Fear not, sweet wench, they shall not touch thee, Kate,I’ll buckler thee against a million.”
“I dare thee but to breathe upon my love.”“Fear not, sweet wench, they shall not touch thee, Kate,I’ll buckler thee against a million.”
“I dare thee but to breathe upon my love.”
“I dare thee but to breathe upon my love.”
“Fear not, sweet wench, they shall not touch thee, Kate,I’ll buckler thee against a million.”
“Fear not, sweet wench, they shall not touch thee, Kate,
I’ll buckler thee against a million.”
And so they do indeed, or against any reasonable number. But there is no combination amongst these banditti. Each comes but to eat his own Aphis, and no one thinksof helping a friend. All therefore are powerless before the organised attack of so fierce a bodyguard. Whilst the ants are with them the Aphides are quite safe, and they are often permanently guarded in this way. Other ants take even more elaborate precautions for the safety of their property, placing them in stalls, where they stand, by plastering earth, etc., about the plant on which they are feeding. Lastly, others still conduct them into their own nest, where they keep them, sometimes, in a chamber specially prepared for their reception, every necessary measure being taken for their proper nourishment, and, as one may say, comfort. Nay, the very eggs of the Aphides are tended by the ants, and hatch out in their own nurseries. Nor is it little for which they do all this, since, taking their size into consideration, the yield of these ant-cows each day must be much greater than that of our own—at least, I should imagine so.
It is not all ants who do these things, nor do any do all of them, but where there are Aphides and also ants, it would seem to be the exception rather than the rule for the latter to neglect them.
But Aphides, though the principal ant-cows of Europe, are not the only ones even there, whilst elsewhere various other species that have this honey-excreting property become their substitutes. “In the tropics,” says Belt, in his much-observing work, “their place is taken in a great measure by species ofcoccidæand genera ofHomoptera, such asMembracisand its allies. My pineapples were greatly subject to the attacks of a small, soft-bodied, brown coccus, that was always guarded by a little blackstinging ant (Solenopsis). This ant took great care of the scale-insects, and attacked savagely any one interfering with them, as I often found to my cost when trying to clear my pines by being stung severely by them. Not content with watching over their cattle, the ants brought up grains of damp earth, and built domed galleries over them, in which, under the vigilant guard of their savage little attendants, the scale insects must, I think, have been secure from the attacks of all enemies.”[47]And again, the same naturalist tells us, “The pawpaw trees growing in my garden were infested by a small brown species ofMembracis—one of the leaf-hoppers that laid its eggs in a cottony nest on the under part of the leaves. The hopper would stand covering the nest until the young were hatched. These were little soft-bodied, dark-coloured insects, looking like Aphides, but more robust, and with the hind segments turned up. From the end of these the little larvæ exuded drops of honey, and were assiduously attended by small ants belonging to two species of the genusPheidole. A third ant—a species ofHypoclinea—which I have mentioned before as a cowardly species, whenever it found any young hoppers unattended, would relieve them of their honey, but would scamper away on the approach of any of thePheidole. The latter do not sting, but they attack and bite the hand if the young hoppers are interfered with.”[47]The latter “are, when young, so soft-bodied and sluggish in their movements, and there are so many enemies ready to prey upon them, that I imagine that in the tropics many species would be exterminated if it were not for the protection of the ants.”[47]
But these leaf-hoppers had not only ants, but wasps to protect them, and there were constant skirmishes and bickerings on their account between the two. The wasp obtained the honey just in the same way as the ants—namely, by stroking the hoppers with its antennæ, and its possession of wings, more than its greater size, gave it a clear advantage over its rival. It did not grapple with the latter, even when there was only a single one to dispute its right, but, rising on the wing, and hovering about till a good opportunity presented itself, it would dart down suddenly on the impertinent little dwarf, and strike it from the leaf or stem. So quick was this action that Mr. Belt could not determine whether it was with the feet or the mandibles that the wasp delivered its blow, but he thinks it was with the former; that is to say, the front pair of them. But in spite of its superiority in single combat, the wasp could not prevail against the numbers of the ants. If, indeed, it was first in the field, there was not much difficulty, for though the leaf would before long be found by some or other of the ants, yet the first arrivals were only pioneers, and when once they were knocked off it it had to be found again, only for a similar fate to befall the new discoverers. Often, however, the wasp would try to clear a leaf already in possession of the ants, and the way to which was known. But in this it was never successful, for though many fell, streams of others came rushing up, so that the wasp had no time to enjoy the fruits of its labours, but was obliged to keep constantly fighting, and before long was tired out. Though a giant amongst pigmies, and having wings—asort of flying-dragon contending with an army of knights—yet it did not despise its small enemies, and evidently dreaded lest any of them should succeed in fastening on it. No doubt it knew—from inheritance, or experience, or both—that an ant clinging to a leg was a difficult thing to get rid of, and to avoid being placed in this position it never fought upon the ground—that is, the leaf—but only on the wing, in the manner described. Had it used its mandibles to bite with, the ants would have seized them, and some might have got on its body. Its sting played no part, doubtless because the small size and hard bodies of the ants would have rendered it ineffective.
We see from the above account that ants are not the only insects that can make discreet use of honey-yielding creatures, though they excel all others in this respect. Wasps have also learnt to milk, if not to stall, their kine, and to wasps, it would seem, must be added—which need not surprise us—at least one species of bee. A correspondent, whose name and date of communication I cannot now remember, says, writing toNature: “Fritz Muller has observed in Brazil a larva of a leaf-hopper—Umbonia indicator—which is used, like the Aphides by the ants, as milch cattle by a species of stingless bee—Trigonia Cagafogo. This bee is fond of oily matters, and feeds on carrion, old stinking cheese, and oil secreted by various plants. Although stingless, it possesses a very intense venom, which causes a most lively irritation of the skin.” I wish I could give the details of a fact so interesting, but have not had the opportunity of reading the original account from which this bald statement is taken. Theants, therefore, have rivals in this industry, and possibly such rivalry may exist to an extent hitherto unsuspected.
Though the protection of these insects by the ants architecturally—by moist earth placed round them, that is to say—is mentioned in the above account, it is not dwelt upon, and seems to play but a small part in the general drama. Some ants, however, rely solely on this method. Mr. Gaudie, writing in theVictorian Naturalist,[48]gives the following account of one of these: “A small species of ant, commonly distributed in the Mallee, has a curious habit of keeping in close confinement a rather large mealy Aphis, which feeds on the stems of young eucalyptus gum trees. Round and over these Aphides the ants construct a domed covering of particles of bark, grass, etc., which serves the double purpose of imprisoning the aphides and excluding other ants. Some of these coverings appear to be entirely closed, whilst others have an opening left in the edges. This doorway is, however, constantly guarded by a pair of ants, which continually move about in the open space, and seem much impressed with the importance of the duty assigned to them. Each enclosure contains generally from three to a dozen Aphides, and about the same number of ants. Upon making a breach in some of these structures for the purpose of observation, I have noticed that many of the live stock were immediately seized by the ants and forcibly removed to a place of safety. The ant under notice is about a quarter of an inch in length, and is of a uniform dark, reddish-brown colour, and formsits ordinary habitation under logs, or in old rotten stumps, and sometimes in the ground. Several other species of ants are very assiduous in their attendance on the various aphides,tettigonidæ, and coccids, but the above is the only kind I have noticed that uses such extraordinary means to secure a monopoly of the much-prized ‘honey-dew.’”
For ants that keep and rear Aphides in their nests we need not go farther than our own little yellow one—Lasius flavus. They guard and look after the eggs of their protégés, which form little black shiny clusters, with the same care that they bestow on their own, and when they are hatched set about providing food for the young aphides. This, it would appear, does not consist of the roots of various plants penetrating the nest itself, for Sir John Lubbock found that the first business of the ants, after the young aphides had appeared, was to conduct or carry them out of the nest, evidently in order that they should find their natural food. None being at hand under these artificial conditions, and the plants required not being known, the poor aphides all died, and this happened again the following year. In the year succeeding to this, however, Sir John was more fortunate, and this is the account he gives of his interesting discovery: “The eggs commenced to hatch the first week in March. Near one of my nests ofLasius flavus, in which I had placed some of the eggs in question, was a glass containing living specimens of several species of plants commonly found on or around ants’ nests. To this some of the aphides were brought by the ants.Shortly afterwards I observed on a plant of daisy, in the axils of the leaves, some small aphides very much resembling those from my nest, though we had not actually traced them continuously. They seemed thriving, and remained stationary on the daisy. Moreover, whether they had sprung from the black eggs or not, the ants evidently valued them, for they built up a wall of earth round and over them. So things remained throughout the summer, but on the 9th of October I found that the aphides had laid some eggs exactly resembling those found in the ants’ nests; and on examining daisy-plants from outside I found on many of them similar aphides and more or less of the same eggs.”[49]
As the young aphides had been brought by the ants to the daisies, and as they had subsequently laid their eggs there, it would certainly seem that the ants are accustomed to collect these eggs from without, and that the aphides do not lay them in the nest. When they are hatched the young aphides, as we have seen, are taken out to feed and lay, and these new eggs laid by them are, in their turn, brought in and tended by the ants. This, as Sir John Lubbock remarks, is a much more remarkable thing than if the aphides, living in the nest with the ants, simply laid their eggs there. In that case they would probably hatch out whether they were tended or not, and it could not be long before the ants would become aware of their value. Here, however, we see this knowledge—how first obtained we know not—exhibited in a more striking manner, and also a great degree of foresight displayed, since as the eggs, except foraccidents, would hatch where they were, it can only be with the idea of providing against these that the ants bring them into their nest. There they are safe from many dangers which threaten them above ground, and are not exposed to the rigours of winter or other climatic vicissitudes.
What are we to say of this act? I think there might be one or two things to say, but Sir John Lubbock says this: “Our ants may not, perhaps, lay up food for the winter; but they do more, for they keep, during six months, the eggs which will enable them to procure food during the following summer—a case of prudence unexampled in the animal kingdom.”[49]There is a slight national note here which should, perhaps, make us suspicious. At least, I am always suspicious when a Frenchman praises anything French, an Englishman anything English—even ants or the climate—a Tierra del Fuegian anything in Tierra del Fuego, and so on. No doubt if prudence really induces the act, it is very great, but if we could imagine any other cause through which the habit might have begun, natural selection would have brought about the rest, since those ants which stored aphides’ eggs would have had more aphides, and consequently more honey-dew to nourish them than those which did not. Now the eggs might at first have been eaten, and so carried down, as provisions, or aphides, brought into the nest, might have laid before they got out again. However the act originated, it is probably a prudential one now, but if the growth of prudence has been aided by that of an inherited habit, having nothing to do with this, it is not quite so remarkable. But what, exactly, does “our” in the above passagemean?Lasius flavusis not confined to England—at least, I suppose not—and if other countries have a claim on its mental powers, our cue should rather be to undervalue them—at least, the note of national vanity should be held in check by the all as powerful one of national prejudice.
Besides these particular aphides, which leave the nest directly after leaving the egg, there are four or five other species which live in it altogether, and feed on the roots of various growing plants. Some nests which I had contained a few, but under natural conditions they are to be found, I believe, in abundance. Special chambers, it would seem, are given up to them, and in Kirby’sMarvels of Ant Lifethere is a picture of such a “subterranean cow-house.” The question arises, where do these aphides lay their eggs, and, if in the nest, does not it largely discount the intelligence, or prudence, attributed toLasius flavusin bringing the other ones into it? In that case, since the eggs of the various species probably resemble one another, any found outside would be brought in by the ants, just as their own larvæ or pupæ would be—or anything else which they value—nor need we ascribe greater foresight to the one act than to the other.
Ants, however, do more wonderful things in relation to aphides than this that Sir John Lubbock has recorded, and if that act is unexampled, as an exhibition of prudence, elsewhere in the animal kingdom, it is not, I think, in this particular branch of it. First it must be remarked that amongst the aphides we have what is called the “alternation of generations,” that is to say a light-loving generation that feeds on the stems and leaves ofupper earth, produces one that loves darkness, whose food is only the underground roots of the plants their parents lived on. This brood in its turn gives birth to another, which forthwith seeks the sun, and so the round goes on. There is this difference in the two broods, that the light-lovers, nevertheless, seek out darkness when the time comes to lay their eggs, whilst the children of darkness lay theirs in the caves where they have, all their lives, lived. That ants should be aware of all this, and habitually adapt their cow-keeping economy to circumstances so recondite, seems very extraordinary, but it would certainly appear to be the case. Thus whenLasius fuliginosus(another Franco-Britannico, etc., species) seesSchizoneura venusta—its particular Aphis—seated on a grass stem, and evidently wishing to lay her eggs, it knows at once what to do. Soft and large, with voluminous wings, such an insect is not well fitted for burrowing. She could hardly do it, in fact, so the ants, recognising this, begin to do it for her, and soon drive a tunnel leading down to the roots of the grass, through which they lead her, first, however, having clipped off her wings, which are now but a useless encumbrance.
Arrived at the terminus, the ants make a proper apartment for their cow Aphis, and here, in the midst of warm sympathisers, and with every comfort and luxury about her, she no longer hesitates to lay her eggs. In due time they hatch, producing wingless aphides, and from the brood thus raised the ants obtain their honey. When, however, this crawling generation have in turn produced another winged one, the ants, far from seeking to detainthese in a place where they would only die, again set to work to make tunnels, through which they conduct them successively to the upper air. One tunnel, one would think, would be sufficient for the purpose; but Lichtenstein, who observed these facts in the south of France,[50]states that each Aphis, as it issues from the egg, has a separate one made for it by the ants. Having reached the surface, these cave-born Ariels spread their wings and fly away. Where they will settle no ant knows, but to the community that has freed them they are lost, probably—they and their eggs—for ever. Do the ants know this? If they do, they do not repine at it, for they know also that the perpetuation of the species, through which alone they can hope for fresh honey, has been provided for. This seems to me altogether to outdo the prudential feat ofLasius flavus, and sinceLasius fuliginosusis distributed probably throughout the greater part of Europe, all the nations that do honour to that portion of the earth’s surface are at equal liberty to think of it with patriotic complacency as “ourant.” For my part, I will only say this, that, whether it is or not, I think it deserves to be a Japanese ant—or that the Japanese, nowadays, much more deserve to have it than we do: that perhaps is the better way of putting it.