Before proceeding to describe the ants, a few remarks may be made on the singular cases and cocoons woven by the caterpillars of certain moths found at Ega.The first that may be mentioned is one of the most beautiful examples of insect workmanship I ever saw.It is a cocoon, about the size of a sparrow's egg, woven by a caterpillar in broad meshes of either buff or rose-coloured silk, and is frequently seen in the narrow alleys of the forest, suspended from the extreme tip of an outstanding leaf by a strong silken thread five or six inches in length.It forms a very conspicuous object, hanging thus in mid-air.The glossy threads with which it is knitted are stout, and the structure is therefore, not liable to be torn by the beaks of insectivorous birds, while its pendulous position makes it doubly secure against their attacks, the apparatus giving way when they peck at it.There is a small orifice at each end of the egg-shaped bag, to admit of the escape of the moth when it changes from the little chrysalis which sleeps tranquilly in its airy cage.The moth is of a dull slatey colour, and belongs to the Lithosiide group of the silk-worm family (Bombycidae).When the caterpillar begins its work, it lets itself down from the tip of the leaf which it has chosen by spinning a thread of silk, the thickness of which it slowly increases as it descends.Having given the proper length to the cord, it proceeds to weave its elegant bag, placing itself in the centre and spinning rings of silk at regular intervals, connecting them at the same time by means of cross threads - so that the whole, when finished, forms a loose web, with quadrangular meshes of nearly equal size throughout.
The task occupies about four days: when finished, the enclosed caterpillar becomes sluggish, its skin shrivels and cracks, and there then remains a motionless chrysalis of narrow shape, leaning against the sides of its silken cage.
Many other kinds are found at Ega belonging to the same cocoon-weaving family, some of which differ from the rest in their caterpillars possessing the art of fabricating cases with fragments of wood or leaves, in which they live secure from all enemies while they are feeding and growing.I saw many species of these; some of them knitted together, with fine silken threads, small bits of stick, and so made tubes similar to those of caddice-worms; others (Saccophora) chose leaves for the same purpose, forming with them an elongated bag open at both ends, and having the inside lined with a thick web.The tubes of full-grown caterpillars of Saccophora are two inches in length, and it is at this stage of growth that I have generally seen them.They feed on the leaves of Melastoniae, and as in crawling, the weight of so large a dwelling would be greater than the contained caterpillar could sustain, the insect attaches the case by one or more threads to the leaves or twigs near which it is feeding.
Foraging Ants--Many confused statements have been published in books of travel, and copied in Natural History works, regarding these ants, which appear to have been confounded with the Sauba, a sketch of whose habits has been given in the first chapter of this work.The Sauba is a vegetable feeder, and does not attack other animals; the accounts that have been published regarding carnivorous ants which hunt in vast armies, exciting terror wherever they go, apply only to the Ecitons, or foraging ants, a totally different group of this tribe of insects.The Ecitons are called Tauoca by the Indians, who are always on the look-out for their armies when they traverse the forest, so as to avoid being attacked.I met with ten distinct species of them, nearly all of which have a different system of marching; eight were new to science when I sent them to England.Some are found commonly in every part of the country, and one is peculiar to the open campos of Santarem; but, as nearly all the species are found together at Ega, where the forest swarmed with their armies, I have left an account of the habits of the whole genus for this part of my narrative.The Ecitons resemble, in their habits, the Driver ants of Tropical Africa; but they have no close relationship with them in structure, and indeed belong to quite another sub-group of the ant-tribe.
Like many other ants, the communities of Ecitons are composed, besides males and females, of two classes of workers, a large-headed (worker-major) and a small-headed (worker-minor) class.
the large-heads have, in some species, greatly lengthened jaws, the small-heads have jaws always of the ordinary shape; but the two classes are not sharply-defined in structure and function, except in two of the species.There is in all of them a little difference among the workers regarding the size of the head; but in some species this is not sufficient to cause a separation into classes, with division of labour; in others, the jaws are so monstrously lengthened in the worker-majors, that they are incapacitated from taking part in the labours which the worker-minors perform; and again, in others the difference is so great that the distinction of classes becomes complete, one acting the part of soldiers, and the other that of workers.The peculiar feature in the habits of the Eciton genus is their hunting for prey in regular bodies, or armies.It is this which chiefly distinguishes them from the genus of common red stinging-ants, several species of which inhabit England, whose habit is to search for food in the usual irregular manner.All the Ecitons hunt in large organised bodies; but almost every species has its own special manner of hunting.
Eciton rapax.--One of the foragers, Eciton rapax, the giant of its genus, whose worker-majors are half-an-inch in length, hunts in single file through the forest.There is no division into classes amongst its workers, although the difference in size is very great, some being scarcely one-half the length of others.
