Atta (genus) - Biology

Biology

The leafcutter ant is morphologically similar to all other Hymenoptera with a body made up of three segments: the head, thorax, and abdomen (gastor). The thorax can be broken down into two major parts: the alitrunk which contains the legs and wings, and the petiole which is found directly anterior to the abdomen (Wilson, E. O.1980). Leafcutter ants can range from 0.1 - 0.65 inches in size. On the head of the leafcutter ant is the antennae. Their antennae are usually fairly long and generally have 10 or more segments. They are the main sensory organs of the insect; the others are the eyes. Leafcutter ants have two kinds of eyes: the 1)compound, lateral eyes, two in number and placed on the sides of the head, and the 2)simple, median eyes, ocelli, or stemmata, of which there are three on the vertex. Both kinds are best developed in the males, less in the females and least in the workers, which often lack the stemmata altogether(Lofgren, C. S.1986). Atta ants have variable morphology in the sizes of their mouth parts and heads across different caste groups. The soldiers have the largest and strongest mandibles which they use for defense and chewing. In addition, they also have the largest heads. In contrast, the worker ants use their jaws for cutting plant material, including leaves and grass, for use to harvest fungus. Atta leafcutter ants have some of the most morphologically diverse workers of any ant. The smallest workers (the minims) mainly work in the nest, caring for the brood and tending the fungus garden. Medium-sized workers (medias) include foragers, who cut the leaves and bring them back to the nest for processing. The largest workers (majors) are usually associated with colony defense. Their suitability as defenders is readily apparent in their large heads, with impressive mandibles powered by large muscles. Their giant, armored heads and sharp, powerful mandibles are formidable weapons. Although they do little else, the soldiers are always ready to rush out of the nest when disturbed to aggressively defend the colony.