The Ecitons in Nicaragua are termed "Army Ants," and they appear regularly to change their hunting grounds in quest of food. Their community comprises males and females, and two kinds of neuters or workers -- a "worker major," or large-headed worker, and a small-headed kind, termed the "worker-minors." The former kind are noted for their elongated jaws; and in some species these forms are denominated "soldiers," their peculiar office being the protection of the community from the attacks of enemies, or the making forays on the nests of other species, or upon other animals.
The habit the Ecitons have of hunting in regular organized bands distinguished them from other and more familiar British species (e.g., Myrmica, the Red Stinging Ant of Britain), which are predatory, but hunt in an irregular and ill-defined manner. One of the best-defined species of foraging ants is the Eciton predator, a small species which hunts in dense hordes, and marches rapidly over a territory. A moving phalanx of this species will extend over from 4 to 6 square yards; and any unwary insect meeting with, or falling into the serried ranks, is soon torn to pieces and devoured. Eciton hamata hunts both in dense masses or in detached columns.
The nature of the prey appears to regulate the mode of march. Thus, when proceeding in columns, Mr Belt found that the Eciton hamata was in search of the nests of another ant (Hypoclinea), the larvae and pupae of which are seized by the Ecitons for the purpose of being brought up as slaves, in accordance with the habits already alluded to. The Hypoclineas rush out on being attacked, bearing their pupae and larvae in their jaws; but the Ecitons at once seize the young ants, although they never appear to injure the parent Hypoclineas. The latter appear a cowardly race, as they make no effort, at self-defence, their habits leading them chiefly to milk aphides, which they desert at once on seeing another and even smaller species of ant approach.
Birds and opossums are terrified, as well as insects, at the Foraging Ants, and frequently fall victims to the determined onslaught of the little furies.
The other species of Ecitons comprise Eciton rapax, the largest of the race, the body of which is half-an-inch in length; Eciton legionis, famed for its ravages on other species of ants (Formicae); Eciton hamata and E. drepanophora, nearly related species; and the so-called Blind Ecitons, thus named from the imperfect condition of the eyes. The E. vastador and E. erratica, species of blind Ecitons, proceed on their raids by means of covered of blind Ecitons, proceed on their raids by means of covered roads or ways, which are excavated and formed in front at a rate corresponding to the advance of the army.
Some interesting information regarding the senses and instincts of the Foraging Ants appears to corroborate the opinions of some earlier observers, already alluded to, on the subject. About a dozen individuals of Eciton hamata were observed to assemble together, as if in consultation, in a tramway excavation in Nicaragua. One ant suddenly left the assembly, and ran up the perpendicular side of the cutting. The example of this first ant was followed by several others, which ran after the first ant for a short distance, then returned, and again proceeded for a farther distance along the track of the first. The object of this proceeding was to make the track readily determinable by the succeeding travellers, and the route of the first individual was unerringly followed by the others, who were at long distance behind. A portion of the trail was removed, when the ants appeared at fault, and occupied themselves in making detours until they again hit upon the interrupted track. On arriving at the top of the excavation, a suitable spot for hunting was descried, when the information appeared to be quickly communicated to those that were below, and the whole army rushed upwards in obedience to the behest of the scouts.
All the Foraging Ants are migratory in habits, and appear to possess no fixed place of abode, but shift their camp at intervals of from four to six or more days. The temporary abode is found in hollow trees, or under fallen trunks.
An Eciton, intentionally imprisoned beneath a stone, was discovered by a companion, who at once informed his neighbours. The other ants then came to the rescue; and by biting at the stone, trying to move it, and seizing the prisoned ant by the legs, they, by their united efforts, set their companion free. An ant embedded in clay, with only the points of the antennae protruding, was discovered by his neighbours, and soon disentombed. And in cases where the efforts of one ant have been inadequate to release a comrade placed in peril, the others were duly informed of the fact, and hurried to assist their less fortunate neighbour.
In crossing a crumbling slope, which was gradually disintegrating under the passage of the ant-army, a portion of the band, by adhering to each other, formed a solid pathway, over which the others passed safely. A twig formed a bridge across a small rill; but this proving insufficient and too narrow for the transit of the army; it was widened by ants clinging to each side of the twig, and in this way the track was broadened sufficiently to admit of the easy passage of the mass.
Such acts would appear to lie beyond the category of purely instinctive processes, since they appear to involve an adaptation of faculties to special cases, and result in special actions being instituted, and thus bear some resemblance to what we familiarly see involved in the process of reasoning characteristic of man's mental powers. The more ordinary operations of ant-life are purely instinctive, as has been already shown; but it may be a matter for consideration if the theory of some naturalists, that the higher development of instinctive powers is akin to reason itself, may not be tenable. Such instances as these just given of the curious and extraordinary acts of the Foraging Ants may serve to show from what circumstances the theory obtains support. Houzeau, in particular, among recent writers, adopts analogous views to these, and maintains that the ants most nearly approach man in the arrangement and general nature of their social existence and condition.
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