These plants are sometimes found along the sides of miniature gullies and crevices in the rock, where they have been washed by little runlets of water formed in seasons of heavy rain, and thus these interloping plants are occasionally dispersed and brought into competition with the rightful occupiers of the ground.
Atta structor and A. barbara do not employ any materials in the construction of their nest, simply excavating it out of the earth itself, or occasionally out of the sandy rock, and the large mounds, in great part composed of vegetable matter, which may frequently be found at the entrances of their nests, are nothing more than the rubbish heaps and kitchen middens of each establishment. These consist in part of the earth pellets and grains of gravel which the ants bring out from their nest when forming the subterranean galleries, but principally of plant-refuse such as the chaff of grasses, empty capsules, gnawed seed-coats, and the like, which would occupy much space if left inside the nest (see Plate I., Fig. A.). While an army of workers are employed in seeking and bringing in supplies, others are busy sorting the materials thus obtained, stripping off all the useless envelopes of seed or grain, and carrying them out to throw away. Thanks to the unwearied activity with which this divided labour is carried on the kitchen middens speedily rise in the harvest season, and in places where they are not exposed to the action of wind and rain, often acquire a considerable size, so much so that sometimes, if collected, one alone might fill a quart tankard.
It was the sight of such a refuse mound, and an examination of the materials which composed it,—many
