Atta spp.

Scientific Name Atta spp.
Common Names English: Giant leafcutter ant; German: Blattschneiderameise; Spanish: hormiga cortadora de las hojas
Description The castes of these ants vary extremely in size, from less of a millimetre for the smallest workers to nearly 2.5 cm (0.97 inch) for the queen.

Biology

Damage

Leafcutter ants harvest leaves from the plants around their nests to use them as substrate for a special fungus, which is their actual source of food. Due to the huge size of their colonies, the consumption of plant material is enormous. In their natural habitat, the ants generally feed on many different plants in turn, removing only a part of their foliage, thus avoiding complete destruction of their substrate source. On cultivated land, however, the plant cover is often less dense than the natural vegetation, and crops mostly lack the defense mechanisms, which the native plants have developed. So an attack by Atta ants can leave the whole stand without a single leaf. Complete defoliation of a citrus tree within 24 hours has been reported.

Lifecycle

Atta spp. live in huge colonies with several millions of individuals. The nests of e.g. A. sexdens can be dug 6 m (19.68 ft) deep into the ground, have a diameter of 10 m (32.8 ft) and a volume of 20 cubic metres. They consist of a great number of about football-sized chambers. Some of these are used for waste, but most for growing fungus and raising larvae. A comparatively small mound above ground is built only from excavated material.

For foraging the insects wander up to 100 m 328 ft) from their nest, on „ant trails“ which they keep free of obstacles. The population in a colony is differentiated in several castes. They are each specialised in a particular task and differ remarkably in size. As with other ants, most of the animals are sterile females, only the queen is fertile. From time to time males and fertile females emerge. As soon as they are mature, they leave the colony on a mating flight. After that the males perish, the females are new queens and each of them will try to found a new colony.

If this is successful the colony can last as long as the queen lives and lays eggs, e.g. 10-15 years in A. sexdens.The genus Atta comprises 15 species, which are found from Texas to south Argentina.

Occurrence

Additional Crop Information

Atta spp. attack almost anything that provides leaves they are able to harvest.

Agricultural Importance

Atta ants are regarded one of the most destructive pests. Where they occur, damage is usually utterly devastating.

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