These belonged to the species called Dinoponera grandis.Its colonies consist of a small number of individuals, and are established about the roots of slender trees.It is a stinging species, but the sting is not so severe as in many of the smaller kinds.There was nothing peculiar or attractive in the habits of this giant among the ants.Another far more interesting species was the Sauba (Oecodoma cephalotes).This ant is seen everywhere about the suburbs, marching to and fro in broad columns.From its habit of despoiling the most valuable cultivated trees of their foliage, it is a great scourge to the Brazilians.In some districts it is so abundant that agriculture is almost impossible, and everywhere complaints are heard of the terrible pest.
The workers of this species are of three orders, and vary in size from two to seven lines; some idea of them may be obtained from the accompanying woodcut.The true working-class of a colony is formed by the small-sized order of workers, the worker-minors as they are called (Fig.I).The two other kinds, whose functions, as we shall see, are not yet properly understood, have enormously swollen and massive heads; in one (Fig.2), the head is highly polished; in the other (Fig.3), it is opaque and hairy.The worker-minors vary greatly in size, some being double the bulk of others.The entire body is of very solid consistency, and of a pale reddish-brown colour.The thorax or middle segment is armed with three pairs of sharp spines; the head, also, has a pair of similar spines proceeding from the cheeks behind.
In our first walks we were puzzled to account for large mounds of earth, of a different colour from the surrounding soil, which were thrown up in the plantations and woods.Some of them were very extensive, being forty yards in circumference, but not more than two feet in height.We soon ascertained that these were the work of the Saubas, being the outworks, or domes, which overlie and protect the entrances to their vast subterranean galleries.
On close examination, I found the earth of which they are composed to consist of very minute granules, agglomerated without cement, and forming many rows of little ridges and turrets.The difference in colour from the superficial soil of the vicinity is owing to their being formed of the undersoil, brought up from a considerable depth.It is very rarely that the ants are seen at work on these mounds; the entrances seem to be generally closed;only now and then, when some particular work is going on, are the galleries opened.The entrances are small and numerous; in the larger hillocks it would require a great amount of excavation to get at the main galleries; but, I succeeded in removing portions of the dome in smaller hillocks, and then I found that the minor entrances converged, at the depth of about two feet, into one broad, elaborately-worked gallery or mine, which was four or five inches in diameter.
This habit of the Sauba ant, of clipping and carrying away immense quantities of leaves, has long been recorded in books on natural history.When employed on this work, their processions look like a multitude of animated leaves on the march.In some places I found an accumulation of such leaves, all circular pieces, about the size of a sixpence, lying on the pathway, unattended by ants, and at some distance from any colony.Such heaps are always found to be removed when the place is revisited the next day.In course of time I had plenty of opportunities of seeing them at work.They mount the tree in multitudes, the individuals being all worker-minors.Each one places itself on the surface of a leaf, and cuts, with its sharp scissor-like jaws, a nearly semicircular incision on the upper side; it then takes the edge between its jaws, and by a sharp jerk detaches the piece.Sometimes they let the leaf drop to the ground, where a little heap accumulates, until carried off by another relay of workers; but, generally, each marches off with the piece it has operated upon, and as all take the same road to their colony, the path they follow becomes in a short time smooth and bare, looking like the impression of a cartwheel through the herbage.
It is a most interesting sight to see the vast host of busy diminutive labourers occupied on this work.Unfortunately, they choose cultivated trees for their purpose.This ant is quite peculiar to Tropical America, as is the entire genus to which it belongs; it sometimes despoils the young trees of species growing wild in its native forests, but seems to prefer, when within reach, plants imported from other countries, such as the coffee and orange trees.It has not hitherto been shown satisfactorily to what use it applies the leaves.I discovered this only after much time spent in investigation.The leaves are used to thatch the domes which cover the entrances to their subterranean dwellings, thereby protecting from the deluging rains the young broods in the nests beneath.The larger mounds, already described, are so extensive that few persons would attempt to remove them for the purpose of examining their interior; but smaller hillocks, covering other entrances to the same system of tunnels and chambers, may be found in sheltered places, and these are always thatched with leaves, mingled with granules of earth.
The heavily-laden workers, each carrying its segment of leaf vertically, the lower edge secured in its mandibles, troop up and cast their burdens on the hillock; another relay of labourers place the leaves in position, covering them with a layer of earthy granules, which are brought one by one from the soil beneath.
