CHAPTER XVII
Do ants sow and reap?—Rival observers—The Texan v. Macaulay’s schoolboy—More evidence wanted—How ants cross rivers—Tubular bridges—Ant armies—A world in flight—Living nests—Ants and plants—Mutual dependence—Nests in thorns and tubers—Ant honey-pots—Business humanity—Burial customs—A strange observation—Two views of ants.
MUSHROOM-GROWING, especially if the ants plant the mushrooms in the way stated by Mr. Tanner, is just as extraordinary, I think, as their habit of planting a field with ant-rice and reaping it at the proper time would be, did they really practise it. Up to a little while ago it certainly seemed as though they did, for there was Dr. Lincecum’s definite statement based upon twelve years’ observation, and this, if not confirmed by Mr. McCook, was, at any rate, not contradicted by him. On the contrary, McCook mentioned a good many facts pointing in the direction of Lincecum’s assertion, and though he did not consider them decisive, he could see no reason why the ants should not act in this way, as indeed there is none: so that as he had only stayed a few months where Lincecum had lived for twelve years, he seemed like a weaker witness supporting, according to his opportunities of observation, a much stronger one. Now, however, comes another witness, whose opportunities have also been great, and in a somewhat heavy-handed way, in a spirit of myth-slaying and irrelevant reference to supposed schoolboy knowledge, hardly required in face of all that ants are known to do, denies the whole thing.
First, however, let us have the assertion as originally made by Lincecum, which is, that on the summit of the mound of their nests, from which they carefully clear away all other vegetation, the harvesting ants sow the seed of a certain plant called ant-rice for the purpose of subsequently reaping a harvest of the grain. It is sown in time for the autumnal rains to bring up, and at the beginning of November a green row or ring of ant-rice, about four inches wide, is seen springing up round the circumference of the disk (as the circular top of the mound is, for some reason, always called). In the vicinity of this circular ring the ants do not permit a single spire of any other grass or weed to remain a day, but leave the aristida or ant-rice untouched until it ripens, which occurs in June of the next year. After the maturing and harvesting of the seed, the dry stubble is cut away and removed from the disk, which is thus left unencumbered until the ensuing autumn, when the same species of grass again appears as before, and so on.[[74]] After stating in a letter to Darwin that he has seen all this taking place year after year, Dr. Lincecum adds:—“There can be no doubt of the fact that the particular species of grain-bearing grass mentioned above is intentionally planted. In farmer-like manner the ground upon which it stands is carefully divested of all other grasses and weeds during the time it is growing. When it is ripe the grain is taken care of, the dry stubble cut away and carried off, the paved area being left unencumbered until the ensuing autumn, when the same ant-rice reappears within the same circle and receives the same agricultural attention as was bestowed upon the previous crop, and so on year after year, as I know to be the case in all situations where the ants’ settlements are protected from graminivorous animals.”[[75]] Lincecum also believed that the ants were able in some way to prevent the seed stored in their nests from germinating. This same fact has been asserted, and apparently proved, by Moggridge, in regard to the harvesting ant of southern Europe, and he also states that, if in spite of the precaution any seeds begin to sprout, the ants by gnawing off the tips of the radicles would prevent the germination from proceeding.
This, then, is the case for the harvesting ant, as we may say; for if these things be true they are certainly much to its credit, whereas, if not, the scandal is so great that it ought to change its name. Let us now hear the case against, as stated by Professor Wheeler, after which readers may make up their minds, if they can, for I have not quite done so yet. I quote in full, so that the two statements may be balanced against each other, and this, I hope, will be more interesting than the usual “Mr. So and So, however, disputes this and thinks, etc.”—another line or two in which the contrary proposition of the one before is stated at about the same length. This is what Professor Wheeler, who “speaks home—you may relish him more (or at least as much) in the soldier as the scholar”—has to say: “It may not be altogether out of place in this paper to record a few other observations on Pogonomyrmex molifacieus, inasmuch as this form has been singled out among all the known members of the genus as presenting certain remarkable instincts. Lincecum is responsible for the myth that this Pogonomyrmex sows a certain species of grass, the ‘ant-rice’ (Aristida oligantha), protects it from harm and frees it from weeds while it is growing, for the purpose of reaping the grain. This notion, which even the Texan schoolboy (not Macaulay’s, who probably knew as much about it) has come to regard as a joke, has been widely cited, largely because the great Darwin stood sponsor for its publication in the Journal of the Linnean Society. McCook, after spending a few weeks in Texas observing the ant in question and recording his observations in a book of 310 pages, failed to obtain any evidence either for or against the Lincecum myth and merely succeeded in extending its vogue by admitting its plausibility. Two years of nearly continuous observation enable me to suggest the probable source of Lincecum’s and McCook’s misconceptions. In either case the observer has started with a few facts, and has then stopped short to draw inferences before gathering more facts. If the nests of Molifacieus be studied during the cool winter months—and this is the only time to study them leisurely and comfortably, since the cold subdues the fiery stings of their inhabitants—the seeds which the ants have garnered in many of their chambers will often be found to have sprouted. It is, therefore, certain that these ants are not able to prevent the seed from germinating, as Moggridge claims for the European species of Messar, except by conveying them to drier chambers; and in protracted spells of wet weather even this precaution seems to be of no avail. On sunny days the ants may often be seen removing these seeds when they have sprouted too far to be left for food, and carrying them to the refuse heap, which is always at the extremity of the cleared earthern disk or mound. In this place the seeds thus cast away as inedible often take root, and, somewhat later, form an arc of tall grass more or less closely approximating to a complete circle round the nest. Since these ants feed largely, though by no means exclusively, on grass-seeds, and since these particular seeds are a very common and favourite article of food, it is easy to see how their grass should often predominate in the circle. In reality, however, only a small percentage of the nests, and only those situated in certain localities, present such circles. Now to state that the ant, like a provident farmer, sows this cereal, and guards and weeds it for the sake of garnering its grain, is as absurd as to say that the family cook is planting and maintaining an orchard when some of the peach-stones which she has carelessly thrown into the backyard, with the other kitchen refuse, chance to grow into peach trees.”[[75]] Certainly such a thing should have been observed before the statement was made, and, if it has not been, the facts seem more probably accounted for on the above explanation.
Professor Wheeler goes on to say that “there are several other facts which show that the special ring of grass about the nest is an unintentional and inconstant result of the activities of the ant colony. For instance, one often finds very flourishing ant-colonies that have existed for years in the midst of much-travelled roads, or in stone side-walls, often a hundred or more feet from any vegetation whatever (without any ant-rice on their mounds therefore). Again, it is very evident that even a complete circle of grass like those described by Lincecum and McCook would be entirely inadequate to supply more than a very small fraction of the grain necessary for the support of a flourishing colony of these ants. Hence they are always obliged to make long trips into the surrounding vegetation, and thereby wear out regular paths, which radiate in different directions, often to a distance of forty to sixty feet from the entrance of the nest. The existence of these paths, which are often found in connection with grass-encircled nests, is alone sufficient to disprove Lincecum’s statements.”[[75]] It certainly seems easier to suppose that Lincecum misinterpreted certain facts, not themselves in dispute, than that an explanation on which so many considerations seem to throw doubt is the correct one. One thing, at least, seems certain—if some of these ant communities grow grain of set purpose, all of them do not. This may be possible, but more proof of it than Lincecum has brought is demanded. If the ants really sow and reap the grain that grows upon their mounds, and, more especially, if they carefully keep the patch clear, it ought not to be difficult to see them doing so. This last would be decisive, whereas the other two are by no means so.
That ants should use their own larvæ like a shuttle, and for the same purpose, seems as strange a thing as one can well imagine, but there is no doubt at all about it, the act having been witnessed on various occasions by competent observers, whose evidence is mutually corroborated. The species in question is common in Eastern Asia, and is accustomed to make little houses or arbours for itself by bending leaves round so that the edges meet, and then fixing them together, as some caterpillars do. Now the larva can do something which the grown ant cannot, which is to spin a cocoon from a sort of gummy, thread-like substance which issues from the mouth. Whilst one group of ants therefore join to keep the leaf bent in the proper position, another take each a larva in their jaws, and pass it from edge to edge of the leaf, applying its mouth to each edge, until the two are bound firmly together.[[76]] Whether this is a more or less remarkable habit than growing mushrooms it would be difficult, perhaps, to decide, nor is there any need to try, since such questions are more interesting left uncertain.
It is well known, or at least credibly asserted, that ants cross rivers by clinging one to another from the branch of a tree overhanging the water, till the end of this living chain, as it becomes longer and longer, is carried by the force of the current to the opposite bank, where a bridge is formed, over which the main body marches.[[77]] According to Du Chaillu the ants in Africa make, not only a bridge, but a tunnel—“a high, safe tubular bridge through which the whole vast regiment marches in regular order.”[[78]] These are the celebrated driver or bashikouay ants, who, when upon their terrible marauding marches, put every living creature, including man, to flight, though for many flight is in vain. Size and strength are here no protection. “The elephant and gorilla fly before them; the black men run for their lives.” So says Du Chaillu, and, sure enough, when the skins of some of the poor gorillas he shot arrived in England, several of these ants were found amongst the hair.[[79]] In the forests of equatorial Africa, abounding—if they have not all been shot by this time—with large animals, these hunting-raids must give rise to some stirring scenes. What crashings through the trees and undergrowth! What uncouth sounds, perhaps, of mingled pain and rage! How a bitten gorilla would express himself! What a subject for a picture if a herd of elephants, a few families of gorillas, a score or so of lions, with a few leopards, and baboons, perhaps a rhinoceros, and any number of antelopes, were all to come rushing down together to where an artist stood ready for them! I should like to see the picture he would draw.