Atta (genus) - Division of Labor

Division of Labor

Head width is an important determining factor in the division of labor for these ants. In a new colony, head width sizes only vary from 0.8-1.6 mm, because workers which tend the gardens must have a head size of less than 1 mm, while 1.6 mm is the smallest head size that can facilitate the cutting of average-toughness vegetation. As a colony grows in size, the queen begins producing individuals with a wider range of head sizes, from 0.7–5 mm. The older the colony becomes, the higher frequency of larger individuals there (Wirth, et al., 2003). This variation in size allows the ants to divide the labor into two main groups; the larger ants are foragers and the smaller ants gardeners. The most common size group for foragers is from 2.0-2.2 mm. These ants bring in foraged leaves and drop them on the floor of a nest chamber. Then, a smaller-sized ant trims the leaves to a size of 1–2 mm across. An even smaller ant balls up the pieces of leaves to cultivate fungus on them. Finally, the smallest ants plant the fungus on the leaves, tend the garden and remove any spores from other species of fungus (Wirth, et al., 2003). The defense of the colony is also divided. When threatened by something such as a large vertebrate animal, the colony deploys its largest workers to defend the colony; however, if defending against something such as other ants, they deploy many smaller workers to repel the threat. In Atta ants, an estimated seven castes split up a total of 20-30 different tasks within the colony (Wirth, et al., 2003).