Eciton burchellii

Eciton burchellii is a species of New World army ant in the genus Eciton. This species, one of the most extensively studied ant species, consists of expansive, organized swarm raids that give it the informal name, Eciton army ant This species displays polymorphic caste features, with the soldier ants having much larger heads and mandibles. The colony lives in bivouacs, which are routinely moved as the foraging paths change. Eciton burchellii colonies cycle between stationary and more active nomadic phases. The colony raids are maintained by the use of pheromones, can be 200 metres (660 ft) long, and employ up to 200,000 ants. Colony members have been observed to fill 'potholes' in the foraging trail, allowing for the faster and easier movement of captured prey back to the nest. Numerous antbirds parasitize the Eciton burchellii by using their raids as a source of food. In terms of geographical distribution, this species is found in the Amazon jungle and Central America. Like most ant species, Eciton burchellii is polymorphic, meaning that features amongst smaller groups within the colony vary in size: a colony contains workers ranging from 3 mm to 12 mm, with each specific 'caste' suited to specialized tasks. At least four castes of workers exist in its social system. Like other species of Eciton, Eciton burchellii features a highly modified soldier caste bearing long, pointed, characteristically falcate (sickle-shaped) mandibles. These features are much larger than on the 'porter caste', the caste directly below that of the major 'soldiers'. Their long legs and elongated body lend them a spider-like appearance. Color varies from deep golden to dark brown. Workers possess single-faceted compound eyes, double-segmented waists, a well-developed sting, and specialized tarsal hooks on their feet with which they cling to one another to form bridges and bivouacs. Eciton burchellii ants are found in the tropical jungles of Central and South America, from Mexico to Paraguay. This species dwells in damp and well-shaded areas, avoiding direct sunlight and high elevations. The species was referred to as Eciton burchellii in the original publication. The double i was subsequently deemed unnecessary in the later 1800s by taxonomists, and hence the name became Eciton burchelli. Recent taxonomic rules, however, adhere more strictly to the original form; the name Eciton burchelli is now largely regarded as invalid. Colonies may be quite large, accommodating as many as 100,000 to 600,000 adult individuals. Each colony consists of a single queen, a brood of developing young, and many adult workers. The adult workers make up the majority of the population. There are four distinct physical worker castes. The queen usually copulates with 10–20 males, which leads to a colony with a large number of worker patrilines, which are full-sibling families with the same father and mother. When a colony's size reaches a maximum, it can result in a split in the colony, with the old queen heading one resultant swarm and a daughter heading the other. The diet and physical upbringing vary among the colony's larvae and is known to determine the physical characteristics of the adult insect. However, caste system determination has also been shown to be influenced by genetic differences. In a study of Eciton burchellii by Jaffé et al. (2007), each individual patriline in 5 colonies was examined. The researchers saw that each patriline had a significantly skewed proclivity for a certain caste, showing that there is considerable evidence for a genetic based caste determination amongst each patriline. These genetic components have been shown not only in Eciton burchellii, but across numerous other ant species—where queens mate with many males, known as polyandry, or where several queens lead a single colony, known as polygyny. Unlike other Hymenoptera species, ants cannot actively thermoregulate through processes such as evaporation, fanning, or incubation. Therefore, they must rely on the location and architecture of their nests in order to regulate their temperature. For species of ants that migrate frequently, such as the Eciton burchellii, the location of the nest may be the most important thermoregulation tool. However, Eciton burchellii does not construct a physical nest. Instead, it builds a living nest out of the individual colony members (called a bivouac). Thermoregulation within these bivouacs is accomplished through the opening or sealing of airways. The colony members can also manipulate the bivouac to avoid rainfall or direct sunlight. Bivouacs are often found in hollow logs, animal burrows in the ground, and hanging in trees. During each nomadic phase, a new nesting site must be found. On average, it takes a colony six to eight hours to move their bivouac. This occurs primarily during the night. Besides being group predators, members of an Eciton burchellii colony cycle between nomadic and stationary (or 'statary') phases. During the twenty-day stationary phase, the pupae and newly laid eggs develop, and the colony goes on raids about every other day. During the fifteen-day nomadic phase, initiated after the eggs hatch and the pupae eclose, the colony goes on raids once every day. Each raid requires approximately one third of the colony, employing up to 200,000 members. The raids can be up to 20 meters in width and 200 meters in length. The raids never occupy the same area twice, so the trail to each new location is always changing. Eciton burchellii colonies avoid locations where they and other colonies have already foraged. This way, they ensure that there are available resources in their foraging area and they avoid any aggressive conspecific encounters. The inbound ants on the trail deliver prey that was captured by the outbound swarming ants.