Formica obtusopilosa

Nests are found under stones or in earthen mounds, similar to those of Myrmecocystus, in fine sandy or loam soils. These ants are very aggressive. Brood was found in nests in June and August, dealate females were found in July. Colonies are probably small, possibly a few hundred workers. One colony also contained workers of Formica aserva, Formica argentea, Formica lasioides and Myrmica. (Mackay and Mackay 2002)

Identification
Just approaching medium-sized, the bicolored (black, or darker brown to reddish brown, gaster with lighter colored, yellowish-red alitrunk and head) Formica obtusopilosa workers have a dense gastric pubescence. This species belongs to the sanguinea species group, which is behaviorally differentiated from other Formica species by their slavemaking habitats. They may be found in colonies that contain a mix of conspecific and heterspecific workers. Morphologically the combination of dense gastric pubescence and an indentation in the middle of the clypeus or, more technically, a median concave impression on the anterior border of the clypeus set sanguinea species apart from other North American Formica. Erect light colored hairs (whitish to whitish yellow) that are larger towards their truncate tips differentiate these ants from other sanguinea species.

Distribution
Minnesota to Alberta and southward to Nebraska, Nevada, Utah, and New Mexico; also northern Mexico.

Distribution based on Regional Taxon Lists
Nearctic Region: Alberta, Canada, Canada, United States. Neotropical Region: Mexico.

Habitat
In New Mexico (Mackay and Mackay 2002) - Sagebrush scrub through meadows, irrigated plains and pinyon-juniper forests up to aspen forests. Cole (1954) found a nest in dry semi-desert.

Biology
This species is a member of a group of Formica species that were formerly placed in the subgenus Raptiformica. All species are facultative slavemakers, i.e., species which usually or often have slaves but can get along without them. The colony-founding female forces her way into a small colony of another species of Formica, somehow gets rid of its queen and workers and appropriates its nest and brood. The workers emerging from this brood accept the intruding queen as their own. The enslaved species belong to the Formica neogagates, fusca, and pallidefulva species groups. When the workers of the slave-making species have become numerous enough, they start raiding for more slaves.

Nests in the soil in open grassy areas. Chambers may be found under stones or there may be a small earthen mound surrounding exposed ground entrances. Colonies can contain up to a few hundred workers.

Nevada, Wheeler and Wheeler (1986) - This species is widely scattered throughout the state. We have 45 records from 29 localities; 3,900-9,000 ft.; but 80% are between 6,000 ft. and 8,000 ft. Fourteen are in the Cool Desert (4 in Atriplex Subclimax and 1 in Sarcobatus Subclimax) and 28 are in the Pinyon-Juniper Biome. We have descriptions of 36 nests: 13 were under stones; of the exposed nests 11 were surmounted by craters, 7 by messy piles of excavated soil, while 5 had no excavated soil (just a hole in the ground). Craters ranged from 5 to 19 cm in diameter, average 14 cm; entrances ranged from 5 to 25 mm in diameter, average 8.6 mm. Workers were fast and timid, erratic (i.e., stopped suddenly and changed direction), but in a populous colony they were aggressive. In 2 colonies we found Formica fusca as slaves.

Nomenclature

 *  obtusopilosa. Formica obtusopilosa Emery, 1893i: 648 (w.) U.S.A. Combination in F. (Raptiformica): Emery, 1925b: 259. Subspecies of sanguinea: Wheeler, W.M. 1901c: 713; Wheeler, W.M. 1913f: 414. Revived status as species: Emery, 1925b: 259; Cole, 1942: 377. Senior synonym of munda: Emery, 1925b: 259; Creighton, 1950a: 465; of alticola: Wilson & Brown, 1955: 128.
 * munda. Formica munda Wheeler, W.M. 1905c: 267 (w.q.) U.S.A. Junior synonym of obtusopilosa: Emery, 1925b: 259; Creighton, 1950a: 465. See also: Wheeler, W.M. 1913f: 416.
 * alticola. Formica munda var. alticola Wheeler, W.M. 1917a: 534 (w.) U.S.A. Combination in F. (Raptiformica): Creighton, 1950a: 466. Subspecies of obtusopilosa: Creighton, 1950a: 466. Junior synonym of obtusopilosa: Wilson & Brown, 1955: 128.