Formica ravida

This mound building ant in the Formica rufa group nests in open areas and feeds on insects and secretions from Homoptera.

Identification
The tentorial pits of this species are shallow. The erect bristles on the tibiae are restricted to two rows on the flexor surface, which extend nearly the entire length of the tibiae. The erect hairs on the gaster are scattered, and do not form an even vestiture when viewed in profile, although the gaster is covered with dense, gray, appressed pubescence. The petiole is narrow in profile with a moderately sharp apex (MacKay & MacKay 2002). There are several short erect hairs coming out of the compound eyes.

Distribution
Western North America.

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

Habitat
Various; from prairies up to pine forests.

Biology
This ant is a presumed temporary social parasite of other species of Formica in the fusca group. It is a very aggressive ant that readily defends its large mound nests by squirting formic acid. Temnothorax andrei may be occasionally found within this mound nest. Incipient F. ravida nests may be found under logs or stones. In northwestern New Mexico on the Navajo Reservation, this ant was found at 1,492 meters elevation near the San Juan River just outside of Shiprock New Mexico in an open pasture. Deep within these host nests, the inquiline ant, Formicoxenus hirticornis has been found.

In Colorado, Gregg (1963) found this species in mixed and deciduous forests, pinyon-juniper woodland, grassland, and sagebrush desert. In North Dakota we (Wheeler and Wheeler, 1977: 10) reported it as a grassland species which preferred shrubby areas, mostly sagebrush. The nest is usually started under a stone or around the base of some small plant (frequently sagebrush). In some nests very little thatch is used, but dome-like thatch mounds are common, averaging 20 cm in height and 60 cm in diameter. The large thatch domes have numerous entrances over all parts of the surface.

Mackay and Mackay (2002) - Nests are usually in the form of thatched mounds on the sides of logs and stumps. Incipient nests may be found under stones or logs, but usually some thatching is present. These ants are extremely aggressive. Workers fold the gaster under the body and squirt a stream of formic acid several centimeters. This acid is strong enough to cause blistered skin, after repeated contact with these ants.

Nevada, Wheeler and Wheeler (1986) - Our 40 records are from 26 localities, which are widely scattered north of the Hot Desert except none in the northwest; 4,300-8,800 ft. Six records were from the Cool Desert (1 from a cottonwood grove), 11 were from the Pinyon-Juniper Biome, and 1from the Coniferous Forest. The nest structure (Fig. 41) is so varied that we give all our recorded descriptions; no two were alike: under horizontal buried sagebrush trunk; thatch mound around rotten log 1 m long; under slightly buried stone with excavated soil at one end of stone; under several contiguous partly buried stones with excavated soil at edge of largest stone; under a slightly buried stone; thatch 15 cm deep on horizontal dead sagebrush trunk and nearby thatch 38 cm in diameter around erect dead sagebrush trunk: a polycalic cluster of 7 thatch mounds 1 ½ - 7 1/2 m apart, each thatch mound on top of a large deeply buried stone except 1 around a dead Purshia trunk, thatch mostly pine needles; asymmetrical thatch mound 94 x 102 cm, of pine needles; asymmetrical thatch mound against a juniper stump, thatch of juniper needles; under old lumber and piece of tin roofing, debris piled around timber; under a log 60 cm long and 30 cm in diameter. Our notes on the behavior of one colony can serve as a sample for the species: fast, aggressive, bite annoying; workers patrolling pine trunks and numerous on the ground; certainly the dominant animal in that habitat.

Nest site selected in open areas devoid of cover or in areas of moderate to sparse cover. Nest begun at the base of some small plant (frequently sagebrush) or under log or stone with many of the passages running into the soil. Moderate to extensive use made of thatching, often little of this visible on the outside of the nest. The finished nest may or may not consist of a large mound of collected detritus. (Creighton, 1940)

Nomenclature

 *  ravida. Formica rufa subsp. ravida Creighton, 1940a: 1, fig. 1 (w.q.m.) U.S.A. [First available use of Formica truncicola subsp. integroides var. ravida Wheeler, W.M. 1913f: 560; unavailable name.] Subspecies of obscuripes: Creighton, 1950a: 493. Raised to species: Gregg 1963: 581. Junior synonym of haemorrhoidalis Creighton: Brown, 1965d: 181. [F. haemorrhoidalis Creighton, 1940a: 1, junior primary homonym of F. haemorrhoidalis Latreille, 1802c: 276.] F. ravida designated as first available replacement name and senior synonym of tahoensis: Bolton, 1995b: 202.
 * haemorrhoidalis. Formica rufa subsp. haemorrhoidalis Creighton, 1940a: 1, fig. 1 (w.) U.S.A. [First available use of Formica rufa subsp. integra var. haemorrhoidalis Emery, 1893i: 652 (w.); Wheeler, W.M. 1913f: 441 (q.m.); unavailable name.] [Junior primary homonym of Formica haemorrhoidalis Latreille, 1802c: 276, above.] Replacement name: ravida Creighton, 1940a: 1 (designated first available replacement name by Bolton, 1995b: 202, as haemorrhoidalis Creighton was raised to species and made senior synonym of ravida and tahoensis by Brown, 1965d: 181).
 * tahoensis. Formica rufa subsp. tahoensis Creighton, 1940a: 1, fig. 1 (w.q.) U.S.A. [First available use of Formica truncicola subsp. integroides var. tahoensis Wheeler, W.M. 1917a: 538; unavailable name.] Cole, 1956g: 260 (q.m.). Subspecies of integra: Creighton, 1950a: 488. Junior synonym of haemorrhoidalis: Brown, 1965d: 181; of ravida: Bolton, 1995b: 205.

Description
This description is taken from Wheeler, W.M. 1913i under the name Formica truncicola subspecies integroides var ravida which is an unavailable name.

Worker. Length 4-6 mm.

Like the var. haemorrhoidalis Emery in pubescence and sculpture and in lacking erect hairs, except on the gaster, but differing in color. The red of the head, thorax, and petiole is much deeper and not yellowish, the legs, whole of the funiculi, tips of the scapes and the gaster are black and even the largest workers have a large black spot on the pro- and mesonotum. In small workers the red color is darker and more brownish, the whole thorax is blackish and the posterior portion of the head and the whole of the scapes are infuscated. The surface of the body in all of the workers is opaque, the pubescence on the gaster short, dense and dark gray in color; the red anal spot is much restricted.

Female. Lengthe 8.5-9 mm.

Differing from the female of haemorrhoidalis in having the tips of the scapes, the posterior border of the pronotum, three spots on the mesonotum, the whole of the scutellum and metanotum, a few spots on the mesoleurae and the middle and hing legs, including their coxae, black.