''Polyergus mexicanus'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

slave-making ant Slave-making ants are brood parasites that capture broods of other ant species to increase the worker force of their colony. After emerging in the slave-maker nest, slave workers work as if they were in their own colony, while parasite workers o ...

in the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus Genus ( plural genera ) is a taxonomic rank used in the biological classifica ...

Formicinae The Formicinae are a subfamily within the Formicidae containing ants of moderate evolutionary development. Formicines retain some primitive features, such as the presence of cocoons around pupae, the presence of ocelli in workers, and lit ...

. 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 In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state' ...

and reliant on ants of another species, ''

Formica ''Formica'' is a genus of ants of the family Formicidae, commonly known as wood ants, mound ants, thatching ants, and field ants. ''Formica'' is the type genus of the Formicidae, and of the subfamily Formicinae. The type species of genus ' ...

'', to undertake these tasks. The parasitic ants are known as "dulotics" (from the Greek δοῦλος ''doulos'', meaning a slave) and the ants they

parasitise Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

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 ''Polyergus breviceps'' is a species of ant endemic to the United States. It is a social parasite of other ants, namely of '' Formica gnava'' but also of '' Formica occulta'' and '' Formica argentea''. ''Polyergus'' is an inquiline parasite, ha ...

''. ''P. mexicanus'' was one of these, a widely distributed species found in western North American and originally described by the Swiss myrmecologist

Auguste Forel Auguste-Henri Forel (1 September 1848 – 27 July 1931) was a Swiss myrmecologist, neuroanatomist, psychiatrist and eugenicist, notable for his investigations into the structure of the human brain and that of ants. For example, he is considere ...

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

''P. 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

tergite A ''tergum'' (Latin for "the back"; plural ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'mar ...

s 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

''P. 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

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s. Further south it is restricted to higher altitudes; in the

Chiricahua Mountains The Chiricahua Mountains massif is a large mountain range in southeastern Arizona which is part of the Basin and Range province of the west and southwestern United States and northwest Mexico; the range is part of the Coronado National Forest. ...

of Mexico it occurs at and in

Chihuahua Chihuahua may refer to: Places * Chihuahua (state), a Mexican state **Chihuahua (dog), a breed of dog named after the state **Chihuahua cheese, a type of cheese originating in the state **Chihuahua City, the capital city of the state **Chihuahua Mu ...

is found at , typically in open coniferous forests.

Behaviour

''P. mexicanus'' is an

obligate parasite An obligate parasite or holoparasite is a parasitic organism that cannot complete its life-cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce. This is opposed to a facultative parasi ...

of other species of ant. These "hosts" are species of ''

'' ants in the groups '' F. fusca'' and '' F. neogagates''. A newly mated female of ''P. mexicanus'' enters the nest of a potential host, employing

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s 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 Brood may refer to: Nature * Brood, a collective term for offspring * Brooding, the incubation of bird eggs by their parents * Bee brood, the young of a beehive * Individual broods of North American Periodical Cicadas: ** Brood X, the largest b ...

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

pupa A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in thei ...

e, prepupae and sometimes late-stage

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e 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