Formica densiventris

Nests are usually found under stones, but may be found in logs and stumps, and under bark, and may be composed entirely of thatching or only partially covered with thatching. The species occurs from prairies, including disturbed, weedy areas, to semiarid scrub up to pinyon-juniper, ponderosa pine-riparian, Douglas fir, and spruce-fir forests. Brood and reproductives have been found in nests in June to August. Workers are very aggressive when the nest is disturbed. Foragers tend aphids. This is one of the most common Formica species in northern New Mexico. It is known to enslave a range of Formica species.

Distribution
Alberta, Canada and the western United States.

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

Habitat
In New Mexico (Mackay and Mackay 2002) - Prairies, including disturbed, weedy areas, to semiarid scrub up to pinyon-juniper, ponderosa pine-riparian, Douglas fir, and spruce-fir forests.

Biology
In New Mexico (Mackay and Mackay 2002): brood and reproductives were found in nests in June to August. A dealate female collected on 3 July 1986. Workers are very aggressive when the nest is disturbed. Foragers tend aphids. This is one of the most common Formica spp. in northern New Mexico.

Nevada, Wheeler and Wheeler (1986) - Our 24 records are from 16 localities, which are widely scattered throughout the state north of the Hot Desert; 5,500-10,000 ft. Five records are from the Pinyon-Juniper Biome, 6 from the Coniferous Forest Biome, and 1 is from the ecotone above it. Four nests were in and under rotten wood, 1 was under a stone, 1 was under a stone surmounted by thatch, and 1 was under a prostrate sagebrush trunk. When a populous nest was disturbed the workers moved rapidly and attacked promptly; the bite was annoying.

Slave Making
Formica pergandei is known to inslave the following species:

Nomenclature

 *  densiventris. Formica fusca var. densiventris Viereck, 1903: 74 (w.) U.S.A. Cole, 1954a: 90 (m.). Junior synonym of subaenescens: Wheeler, W.M. 1913f: 504. Revived from synonymy as subspecies of fusca: Brown, 1947: 7. Raised to species: Creighton, 1950a: 499. Senior synonym of spicata: Cole, 1954a: 89; Cole, 1955b: 50; of rasilis: Mackay, Lowrie, et al. 1988: 114.
 * rasilis. Formica microgyna var. rasilis Wheeler, W.M. 1903e: 648 (w.q.m.) U.S.A. Subspecies of microgyna: Wheeler, W.M. 1913f: 468. Raised to species: Creighton, 1950a: 506. Junior synonym of densiventris: Mackay, Lowrie, et al. 1988: 114.
 * spicata. Formica rasilis subsp. spicata Creighton, 1950a: 507 (w.q.m.) U.S.A. [First available use of Formica microgyna subsp. rasilis var. spicata Wheeler, W.M. 1913f: 469; unavailable name.] Material of the unavailable name pinetorum referred here by Creighton, 1950a: 507. Junior synonym of densiventris: Cole, 1954a: 89; Cole, 1955b: 50.

Taxonomic Notes
The nomenclature and status of this ant have been very complicated. The description by Viereck (1903) is brief and completely inadequate, and based on two poorly preserved specimens (Brown, 1947). This has created considerable confusion. A number of species and subspecies have been synonymized with F. densiventris (Creighton, 1950; Cole, 1955b). Wheeler (1903c) described a taxon, F. rasilis based on workers, queens and males. Subsequently hybridization was observed between F. rasilis and F. densiventris (Creighton, 1950; Cole, 1955b; Gregg, 1963). Because of this, Gregg chose to consider F. densiventris as a subspecies of F. rasilis. We do not recognize a separate subspecies and due to precedence of date of publication (Viereck: Jan 1903; Wheeler: Nov 1903c) we consider the proper name of the species to be Formica densiventris Viereck (Mackay et al. 1988).