Polyergus

Taxobox | name = "Polyergus"
regnum = Animalia
phylum = Arthropoda
classis = Insecta
ordo = Hymenoptera
familia = Formicidae
subfamilia = Formicinae
genus = "Polyergus"
genus_authority = Latreille, 1804
subdivision_ranks = Species
subdivision =
* "Polyergus breviceps" western North America (probably includes several distinct species)
* "Polyergus lucidus" eastern North America to the Rockies
* "Polyergus lucidus longicornis eastern North America (considered a distinct species by knowledgeable myrmecologists, but this not yet formalized)
* "Polyergus nigerrimus" Mongolia, Tuvan republic
* "Polyergus rufescens" Europe, western Asia
* "Polyergus samurai" Japan, Korea, eastern China
* "Polyergus texanus" (identity of this taxon uncertain, but unlikely to be a true "Polyergus")

"Polyergus", or Legionnaire ant, 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 solely as a ruling caste, maintaining a worker force by capturing ants of the closely related genus "Formica" in massive colony-to-colony raids. The captured ants are generally referred to as "slaves" in scientific literature, though recent attempts have been made to apply other human cultural models, such as describing the ruling caste as "parasites" or "raiders" and the servant caste as "hosts", "help-ants", or "domesticated animals".

"Polyergus" obtains its "Formica" work force by stealing pupae from nearby "Formica" colonies and carrying them back to its 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 kills the existing "Formica" queen (immediately if workers are present, later if these are not yet reared) and becomes accepted by the "Formica" workers. These proceed to rear the first and all subsequent "Polyergus" 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.

References

*Cite web |author=Dale Ward |year=2005 |url=http://www.tightloop.com/ants/polbre.htm |title=Ants of Arizona: "Polyergus breviceps" (Slave Raiding Ant)