Polyergus
From Wikipedia, the free encyclopedia
| Polyergus | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Scientific classification | ||||||||||||||
|
||||||||||||||
| Species | ||||||||||||||
|
Polyergus is a small genus of 6 described species (and several possible undescribed species) of "slave-raiding" ants, sometimes called Amazon ants. Its workers are incapable of caring for brood, in part due to their dagger-like, piercing mandibles, but more importantly, because in the evolution of their parasitism, they have lost the "behavioral wiring" to carry out even rudimentary brood care, or even to feed themselves. Polyergus species subsist as social parasites, maintaining a worker force by capturing ants of the closely related genus Formica in massive colony-to-colony raids. Until recently, the Formica workers that live with Polyergus have been referred to, unquestioningly, as "slaves". The situation under which the Formica workers live in a Polyergus nest is more comparable to that of domesticated and spayed work animals, so it may be preferable to simply refer to the two species in this relationship as parasite and host, raider and help-ants, or some other more appropriate terms.
Polyergus obtains its Formica work force by stealing pupae from nearby Formica colonies and carrying them back to their own nest, by means of spectacular raids, conducted on hot, summer afternoons. Back in the Polyergus nest, Formica workers are eventually helped to emerge from the cocoons by Formica workers already living there. The new workers quickly assimilate the characteristic odor of the mixed-species population of the Polyergus colony -- completely without violence or coercion. The newly hatched "slaves" go on to nurse, forage, and perform other colony upkeep duties. As far as is known, all established Polyergus colonies have only one queen. To found a new colony, a lone Polyergus queen invades a nest of the host species, or encounters and moves in with a colony-founding queen of the host species. In the latter case, the host queen is allowed to survive until she has reared a number of host workers, something the Polyergus queen cannot do herself. A young Polyergus queen ultimately kills the existing Formica queen (right away if workers present, later if these are not yet reared) and becomes accepted by the Formica workers. These proceed to rear the first and all subsequent Amazon ant workers. Clearly, this complicated and lengthy process often fails, as Polyergus colonies are relatively rare, even though each mature colony produces dozens or hundreds of new potential queens each year. To counteract the natural mortality of the Formica worker population, Polyergus workers must conduct regular raids over a 6-8 week period, every summer over the 10-15 year life span of their colony.
The raids of Amazon ants have been sensationalized as "blood baths" in popular writing. However, scientific study has demonstrated repeatedly and for all species that their brood stealing raids are highly efficient and virtually non-violent. It is rare for even a single member of the raided host colony to be injured or killed. Instead, the host colony is overwhelmed, apparently by its own formic acid and alarm pheromones produced in the panic, when the marauders enter their nest en masse. Commonly, the queen and workers of the raided Formica colony evacuate up nearby vegetation and simply "wait for the problem to go away" while the Polyergus workers find and run off with their brood.
[edit] References
- Dale Ward (2005). Ants of Arizona: Polyergus breviceps (Slave Raiding Ant).
