Polyergus Mexicanus

''Polyergus mexicanus'' is a species of slave-making ant in the subfamily Formicinae. It is the most widely distributed species of ''Polyergus'' in North America. It is an obligatory social parasite, unable to feed itself or look after the colony and reliant on ants of another species, ''Formica'', to undertake these tasks. The parasitic ants are known as "dulotics" (from the Greek δοῦλος ''doulos'', meaning a slave) and the ants they parasitise are known as "hosts".

Taxonomy

In a revision of the genus ''Polyergus'' in 2013, Trager reinstated five species previously thought to be synonymous with ''Polyergus breviceps''. ''P. mexicanus'' was one of these, a widely distributed species found in western North American and originally described by the Swiss myrmecologist Auguste Forel in 1899, the type locality being Mexico. It is likely that most species mentioned in scientific journals as ''P. breviceps'' are in fact ''P. mexicanus''.

Description

''Polyergus mexicanus'' is somewhat variable across its range and averages in total length. The head is glossy in the south of its range and more matte in eastern and northern populations. The mesonotum is matte dorsally and usually shining laterally. The gaster is also shining but this is partially concealed by a covering of short erect hairs, especially dorsally. The colour is generally red with the posterior portion of the tergites being tinged with brown. The legs may be a slightly darker colour than the body, and the hairs on the dorsal surface are grey, never yellowish as they are in ''P. breviceps''. This species also bears longer brownish macrosetae (hairs) but they often get worn away, leaving dark scars on the tergites.

Distribution and habitat

''Polyergus mexicanus'' is the most widely distributed species in the genus ''Polyergus'' in North America. It is native to the western United States and Canada, North Dakota, South Dakota, Arkansas and Mexico. It usually inhabits open woodland with little undergrowth or mixed wood and grassland habitats. Further south it is restricted to higher altitudes; in the Chiricahua Mountains of Mexico it occurs at and in Chihuahua is found at , typically in open coniferous forests.

Behaviour

''Polyergus mexicanus'' is an obligate parasite of other species of ant. These "hosts" are species of ''Formica'' ants in the groups '' F. fusca'' and '' F. neogagates''. A newly mated female of ''P. mexicanus'' enters the nest of a potential host, employing pheromones to subdue the resident workers. She then kills the existing ''Formica'' queen and becomes accepted by the ''Formica'' workers. These then proceed to rear her brood as well as maintaining the nest and feeding the dulotic queen and the ants which develop from the eggs she lays. The dulotic ants are unable to carry out these tasks themselves.

The workforce of the colony is periodically replenished by a raid being undertaken on another nearby colony of ''Formica'' ants. The raid is made by the ''Polyergus'' worker ants and usually takes place on a hot afternoon in the summer. A scout ant locates a suitable target nest and a column of dulotic ants move towards it. On arriving at the nest they may mill around for a while, perhaps clearing debris such as small stones or twigs away from the entrance. They then surge inside and quickly begin to emerge carrying host pupae, prepupae and sometimes late-stage larvae back to the dulotic nest. There, the host workers care for them as well as the dulotic young developing from eggs laid by the ''Polyergus'' queen. Newly mated female dulotics may take advantage of raids to enter host colonies during the chaotic situation that exists during a raid.

References

{{Taxonbar, from=Q16757635

Formicinae
Slave-making ants
Hymenoptera of North America
Insects described in 1899
Taxa named by Auguste Forel