Animal Behavior/Army Ants - Social Hierarchy, Life Cycles, and Migration

Army Ants (Eciton burichelli)

Army ant colony castes consist of queen ants, soldier ants, and multi-purpose worker ants. In the army ant colony, the queen ant lays eggs, the soldiers focus their attention to the defense of the colony, and the worker ants are split between being foragers or tending to the queens brood.

The Army ant is abundantly found in humid lowland forests or heavily forested areas of Central/South America. The changes in temperature and precipitation have no effect on the life cycles or migration of these ants.

The social structure and life cycles of army ants have two distinct phases. Army ant colonies go through a stationary phase and a migratory (nomadic) phase. The phases are based on the ability of a queen to produce many eggs in a very short period of time (from 100 000 to 300 000 eggs in five to ten days); thus, the queen overpopulates a given area, which then triggers migration of the colony.

In the stationary phase, the army ant queen's abdomen swells to hold 55 000 to 66 000 eggs. As the eggs develop into mature ants, tens of thousands of adult workers appear, triggering the nomadic phase: colony activity increases exponentially, and "swarm raids" increase in size and intensity. With a colony of this size, the army ant colony must emigrate daily. The migration continues until "larval pupation" begins. Once this occurs, the colony re-enters the stationary phase, and the cycle repeats.

Due to their large colony sizes, army ants migrate in order to find food. Most ants are "column feeders." Army ants are what are called "swarm feeders." The foraging workers form a fan-shaped swarm with a broad front. Along with feeding, army ants also have a unique way of forming nests. The army ant nest is made up of army ants themselves. The ants form walls and fasten onto each other by using their mandibles. The ant colony forms these walls almost anywhere in order to enclose the queen and her brood. The nest is very structured, as it provides corridors within itself for transporting food and eggs throughout the many areas of the nest.

Army ant colonies march and nest in different phases as well. In the nomadic phase, army ants march at night and stop to camp during the day. The colony begins a nomadic phase when available food has decreased. During this phase, the colony makes temporary nests that are changed everyday. Each of these nomadic rampages or marches lasts for approximately 17 days.

Army ants are notorious for eating anything that gets in their path. They can kill and eat up to 100 000 animals in a day! They normally consume lizards, snakes, chickens, pigs, goats, scorpions, tarantulas, beetles and other ants. Army ants can also climb trees, and feed on animals within its canopy.

Army ants communication is completely dependent on chemical messaging and trail pheromones. These methods of communication act as a stimuli for changing behavior patterns. Unlike other ants, army ants do not have compound eyes, but instead have single eyes. Army ants are also blind and have to use their antennae to sense smell and touch. The army ants use these senses to communicate in nesting and raiding.

Works Cited

Alcock, John. Animal Behavior. 7th editionSinauer Associates, Inc.: Sunderland, 2001.

The Raiders http://www.ex.ac.uk/bugclub/raiders.html

Insecta Inspecta http://www.insecta-inspecta.com/ants/army/

Animal Diversity Web http://animaldiversity.ummz.umich.edu/site/index.html