The road led towards a cocoa plantation, and here I soon discovered the building which I afterwards visited daily. As I again went thither one day I was met, at a considerable distance from the nest, by a closely pressed column coming thence, and all the ants laden with leaves, beetles, pupæ, butterflies, &c.; the nearer I came to the nest, the greater was the activity. It was soon plain to me that the ants were in the act of leaving their dwelling, and I walked along the train to discover the new abode. They had gone for some distance along the old road, and had then made a new one through the grass to a cooler place, lying rather higher. The grass on the new road was all bitten off close to the ground, and thousands were busy carrying the path on to the new building. At the new home itself was an unusual stir of life. There were all sorts of labourers—architects, builders, carpenters, sappers, helpers. A number were busy digging a hole in the ground, and they carried out little pellets of earth and laid them together on end to make a wall. Others drew along little twigs, straws, and grass-stalks, and put them near the place of building. I was anxious to know why they had quitted their old home, and when the departure was complete, I dug it up with a spade. At a depth of about a foot and a half I found several tunnels of a large marmot species, the terror of cocoa planters, because in making their passages they gnaw off the thickest roots of the cocoa plants. The interior of the ant-hill had apparently fallen in through these mines. Unfortunately I was unable to follow further the progress of the new building, for I was obliged to leave the next day for San Juan del Sur. When I returned at the end of a week the building was finished, and the whole colony was again busy with the leaves of the coffee plants.
Harvesting Ants (Atta).—The ants which, so far as at present known, practise the peculiar and distinctive habits to be described under this division belong for the most part to one genus, Atta, which, however, comprises a number of species distributed in localised areas over all the four quarters of the globe. Hitherto nineteen species have been detected as having the habits in question. These consist of gathering nutritious seeds of grasses during summer, and storing them in granaries for winter consumption. We owe our present knowledge concerning these insects to Mr. Moggridge,[34] who studied them in the south of Europe, Dr. Lincecum,[35] and Mr. MacCook,[36] who studied them in Texas, and Colonel Sykes[37] and Dr. Jerdon,[38] who made some observations upon them in India. They also occur scattered over a great part of Europe and in Palestine, where they were clearly known to Solomon and other classical writers of antiquity,[39] whose claim to accurate observation, although long disputed (owing to the authority of Huber), has now been amply vindicated.
Mr. Moggridge, who was a careful and industrious observer, found the following points of interest in the habits of the European harvesters. From the nest in various directions there proceed outgoing trains, which may be from twenty to thirty or more yards in length, and each consists of a double row of ants, moving, like the leaf-cutting ants, in opposite directions. Those in the outgoing row are empty-handed, while those in the incoming row are laden. But here the burdens are grass seeds. The roads terminate in the foraging ground, or ant-fields, and the insects composing the columns there become dispersed by hundreds among the seed-yielding grasses. The following is their method of collecting seeds; I quote from Moggridge:—
It is not a little surprising to see that the ants bring in not only seeds of large size and fallen grain, but also green capsules, the torn stalks of which show that they have been freshly gathered from the plant. The manner in which they accomplish this feat is as follows. An ant ascends the stem of a fruiting plant of shepherd's-purse (Capsella bursa-pastoris), let us say, and selects a well-filled but green pod about midway up the stem, those below being ready to shed their seeds at a touch. Then, seizing it in its jaws, and fixing its hind legs firmly as a pivot, it contrives to turn round and round, and so strain the fibres of the fruit-stalk that at length they snap. It then descends to the stem, patiently backing and turning upwards again as often as the clumsy and disproportionate burden becomes wedged between the thickly set stalks, and joins the line of its companions on their way to the nest. In this manner capsules of chickweed (Stellaria media) and entire calyces, containing the nutlets of calamint, are gathered; two ants also sometimes combine their efforts, when one stations itself near the base of the peduncle and gnaws it at the point of greatest tension, while the other hauls upon and twists it. I have never seen a capsule severed from its stalk by cutting alone, and the mandibles of this ant are perhaps incompetent to perform such a task. I have occasionally seen ants engaged in cutting the capsules of certain plants, drop them, and allow their companions below to carry them away; and this corresponds with the curious account given by Ælian of the manner in which the spikelets of corn are severed and thrown down 'to the people below,' τῷ δήμῳ τῷ κάτω.
The recognition of the principle of the division of labour which the latter observation supplies, is further proved by the following quotation from the same author. A dead grasshopper which was being carried into their nest was—
Too large to pass through the door, so they tried to dismember it. Failing in this, several ants drew the wings and legs as far back as possible, while others gnawed through the muscles where the strain was greatest. They succeeded at last in thus pulling it in.
The same thing is strikingly shown by the following quotation from Lespès:—
If the road from the place where they are gathering their harvest to the nest is very long, they make regular depôts for their provisions under large leaves, stones, or other suitable places, and let certain workers have the duty of carrying them from depôt to depôt.