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Yet, whatever the simile, the net of unconscious precedent is too closely drawn, the mesh of instinct is too fine to hope for any initiative. This was manifested by the most significant and spectacular occurrence I have ever observed in the world of insects. One year and a half ago I studied and reported upon, a nest of Ecitons or army ants.
On digging into the earth with a small trowel near the entrances of the mines, I found the nests of the Formicae, with grubs and cocoons, which the Ecitons were thus invading, at a depth of about eight inches from the surface.
The place was a tract of open ground near the river side, just outside the edge of the forest, and surrounded by rocks and shrubbery. A dense column of Ecitons was seen extending from the rocks on one side of the little haven, traversing the open space, and ascending the opposite declivity. The length of the procession was from sixty to seventy yards, and yet neither van nor rear was visible.
About the nest which they are harrying everything is confusion, Ecitons run here and there and everywhere in the greatest haste and disorder; but the result of all this apparent confusion is that scarcely a single Hypoclinea gets away with a pupa or larva. I never saw the Ecitons injure the Hypoclineas themselves, they were always contented with despoiling them of their young.
It keeps them together, and prevents individual ants from starting off alone after objects that, if their eyesight were better, they might discover at a distance. The Ecitons and most other ants follow each other by scent, and, I believe, they can communicate the presence of danger, of booty, or other intelligence, to a distance by the different intensity or qualities of the odours given off.
In about two hours, all the nests of Formicae were rifled, though not completely, of their contents, and I turned towards the army of Ecitons, which were carrying away the mutilated remains.
We timed the laden Ecitons and found that they averaged two to two and three-quarter inches a second. So a given individual would complete the round in about two hours and a half. Many guests were plodding along with the ants, mostly staphylinids of which we secured five species, a brown histerid beetle, a tiny chalcid, and several Phorid flies, one of which was winged.
The armies of E. legionis consist of many thousands of individuals, and move in rather broad columns. They are just as quick to break line, on being disturbed, and attack hurriedly and furiously any intruding object, as the other Ecitons. The species is not a common one, and I seldom had good opportunities to watch its habits. The first time I saw an army was one evening near sunset.
They soon penetrate every part of the confused heap, and then, gathering together again in marching order, onward they move. All soft-bodied and inactive insects fall an easy prey to them, and, like other Ecitons, they tear their victims in pieces for facility of carriage.
In a very short space of time the information was communicated to the ants below, and a dense column rushed up to search for their prey. The Ecitons are singular amongst the ants in this respect, that they have no fixed habitations, but move on from one place to another, as they exhaust the hunting grounds around them. I think Eciton hamata does not stay more than four or five days in one place.
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