Guatemala

by William Tufts Brigham

LEAF-CUTTING ANTS.

The Œcodoma, Zompopos, or leaf-cutting ants, are such a pest to the fruit-growers of Central America that I have quoted from Mr. Belt the most satisfactory account of their habits that has ever been published. He says:—

“The first acquaintance a stranger generally makes with them is on encountering their paths on the outskirts of the forest crowded with the ants,—one lot carrying off the pieces of leaves, each piece about the size of a sixpence and held up vertically between the jaws of the ant, another lot hurrying along in an opposite direction empty handed, but eager to get loaded with their leafy burdens. If he follows this last division, it will lead him to some young trees or shrubs, up which the ants mount, and where each one, stationing itself on the edge of a leaf, commences to make a circular cut with its scissor-like jaws from the edge, its hinder feet being the centre on which it turns. When the piece is nearly cut off, it is still stationed upon it, and it looks as though it would fall to the ground with it; but on being finally detached, the ant is generally found to have hold of the leaf with one foot, and soon righting itself, and arranging its burden to its satisfaction, it sets off at once on its return. Following it again, it is seen to join a throng of others, each laden like itself, and without a moment’s delay it hurries along the well-worn path. As it proceeds, other paths, each thronged with busy workers, come in from the sides, until the main road often gets to be seven or eight inches broad, and more thronged than the streets of the city of London.

“After travelling for some hundreds of yards, often for more than half a mile, the formicarium is reached. It consists of low wide mounds of brown clayey-looking earth, above and immediately around which the bushes have been killed by their buds and leaves having been persistently bitten off as they attempted to grow after their first defoliation. Under high trees in the thick forest the ants do not make their nests, because, I believe, the ventilation of their underground galleries, about which they are very particular, would be interfered with, and perhaps to avoid the drip from the trees. It is on the outskirts of the forest, or around clearings or near wide roads that let in the sun, that these formicariums are generally found. Numerous round tunnels, varying from half an inch to seven or eight inches in diameter, lead down through the mounds of earth; and many more from some distance around also lead underneath them. At some of the holes on the mounds ants will be seen busily at work bringing up little pellets of earth from below and casting them down on the ever-increasing mounds, so that its surface is nearly fresh and new-looking....

“The ceaseless toiling hosts impress one with their power, and one asks, What forests can stand before such invaders? How is it that vegetation is not eaten off the face of the earth? Surely nowhere but in the tropics, where the recuperative powers of Nature are immense and ever active, could such devastation be withstood.... None of the indigenous trees appear so suitable for them as the introduced ones....

“In June, 1859, very soon after the formation of my garden, the leaf-cutting ants came down upon it, and at once commenced denuding the young bananas, orange, and mango trees of their leaves. I followed up the paths of the invading hosts to their nest, which was about one hundred yards distant, close to the edge of the forest. The nest was not a very large one, the low mound of earth covering it being about four yards in diameter. At first I tried to stop the holes up; but fresh ones were immediately opened out. I then dug down below the mound and laid bare the chambers beneath, filled with ant-food and young ants in every stage of growth. But I soon found that the underground ramifications extended so far and to so great a depth, whilst the ants were continually at work making fresh excavations, that it would be an immense task to eradicate them by such means; and notwithstanding all the digging I had done the first day, I found them as busily at work as ever at my garden, which they were rapidly defoliating. At this stage our medical officer, Dr. J. H. Simpson, came to my assistance, and suggested the pouring carbolic acid, mixed with water, down their burrows. The suggestion proved a most valuable one. We had a quantity of common brown carbolic acid, about a pint of which I mixed with four buckets of water, and, after stirring it well about, poured it down their burrows. I could hear it rumbling down to the lowest depths of the formicarium, four or five feet from the surface. The effect was all that I could have wished; the marauding parties were at once drawn off from my garden to meet the new danger at home. The whole formicarium was disorganized. Big fellows came stalking up from the cavernous regions below, only to descend again in the utmost perplexity.

“Next day I found them busily employed bringing up the ant-food from the old burrows and carrying it to a new one a few yards distant; and here I first noticed a wonderful instance of their reasoning powers. Between the old burrows and the new one was a steep slope. Instead of descending this with their burdens, they cast them down on the top of the slope, whence they rolled down to the bottom, where another relay of laborers picked them up and carried them to the new burrow. It was amusing to watch the ants hurrying out with bundles of food, dropping them over the slope and rushing back immediately for more. They also brought out great numbers of dead ants that the fumes of the carbolic acid had killed. A few days afterwards, when I visited the locality again, I found both the old burrows and the new one entirely deserted, and I thought they had died off; but subsequent events convinced me that the survivors had only moved away to a greater distance. It was fully twelve months before my garden was again invaded. I had then a number of rose-trees, and also cabbages growing, which the ants seemed to prefer to everything else. The rose-trees were soon defoliated, and great havoc was made amongst the cabbages. I followed them to their nest, and found it about two hundred yards from the one of the year before. I poured down the burrows, as before, several buckets of water with carbolic acid. The water is required to carry the acid down to the lowest chambers. The ants, as before, were at once withdrawn from my garden; and two days afterwards, on visiting the place, I found all the survivors at work on one track that led directly to the old nest of the year before, where they were busily employed making fresh excavations. Many were bringing along pieces of the ant-food from the old to the new nests; others carried the undeveloped white pupæ and larvæ. It was a wholesale and entire migration; and the next day the formicarium down which I had last poured the carbolic acid was entirely deserted.

“Don Francisco Velasquez informed me in 1870 that he had a powder which made the ants mad, so that they bit and destroyed each other. He gave me a little of it, and it proved to be corrosive sublimate. I made several trials of it, and found it most efficacious in turning a large column of the ants. A little of it sprinkled across one of their paths in dry weather has a most surprising effect. As soon as one of the ants touches the white powder it commences to run about wildly, and to attack any other ant it comes across. In a couple of hours round balls of the ants will be found all biting each other; and numerous individuals will be seen bitten completely in two, whilst others have lost some of their legs or antennæ. News of the commotion is carried to the formicarium, and huge fellows, measuring three quarters of an inch in length, that only come out of the nest during a migration or an attack on the nest or one of the working columns, are seen stalking down with a determined air, as if they would soon right matters. As soon, however, as they have touched the sublimate, all their stateliness leaves them; they rush about, their legs are seized hold of by some of the smaller ants already affected by the poison, and they themselves begin to bite, and in a short time become the centre of fresh balls of rabid ants.”[67]

I wish I could quote all Mr. Belt’s interesting article; for his conclusion as to the use the ants make of the bits of leaf they are so incessantly collecting, is an ingenious one, and probably true. It is certain that the little fellows are never seen taking a nibble of their burdens, which would probably be the case if this material was intended for food; and Mr. Belt thinks that the smaller ants, who seldom leave the nest and never carry leaves, have the task of cutting the leaves up into very small bits, which serve as manure for a minute fungus, which is the real ant-food. It seems that “some of the ants make mistakes, and carry in unsuitable leaves; thus grass is always rejected by them. But I have seen some ants, perhaps young ones, carrying leaves of grass; but after a while these pieces are always brought out again and thrown away. I can imagine a young ant getting a severe ear-wigging from one of the major-domos for its stupidity.”