Formica difficilis

Formica difficilis is an ecologically conservative grassland ant species of eastern USA, which once was common in prairies and natural meadows, but now is rare and very sporadic due to nearly total destruction or degradation of suitable habitat. It is a member of the F. microgyna group and is generally found in areas where there are large populations of its temporary host, Formica incerta. It is one of the more heat-tolorant species within the microgyna species group.

Identification
Posterior margin of head and pronotum with sparse short, spatulate or distally flattened and broadened hairs and head slightly shinier than mesosoma.

The scape of workers of this species are without erect or suberect hairs (except at the apex). The tibiae lack erect hairs, except for a row of bristles along the flexor surface. The pronotum and mesonotum have several, erect, blunt-tipped hairs, the propodeum may lack hairs or may have a few. The petiole always has at least a few hairs on the apex and on the sides, the gaster has several scattered hairs.

The queens are tiny, yellow specimens, slightly smaller than the largest workers. The scapes are without erect hairs, the tibiae are without erect hairs except for a row of bristles on the flexor surface. The dorsum of the head has a number of erect hairs, the ventral surface has few erect hairs the dorsum of mesosoma has numerous erect hairs as does the petiole and the gaster. Most hairs are sharp-tipped, except for a few on the mesosoma that have blunt tips.

This species could be confused with Formica querquetulana, but differs in that the head is slightly more shiny  than the mesosoma, and their are at least a few hairs present on the posterior lateral corner of the head. It is difficult to separate this species from Formica indianensis, and Formica postoculata, both of which may be synonyms. It can usually be separated on the basis of several erect hairs on the apex of the petiole, which are missing in the other two species. It differs from F. indianensis as there are a number of erect hairs on the dorsum of the head, which are reduced in number in F. indianensis (to 6 of fewer).

Distribution
Eastern United States, roughly co-extensive with its usual temporary host (during colony foundation), Formica incerta.

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

Biology
This species occurs in native loamy or sandy grasslands, old fields, lightly grazed pasture and barrens. It avidly tends aphids and membracids and visits extrafloral nectaries on prairie plants, as well as preying on (mostly) small, soft-bodied invertebrates. It is attracted to both sweet and meat baits.

New colonies are established when the small F. difficilis queen invades an existing colony of F. incerta (whose workers they somewhat resemble), or when it re-entering an established colony of its own species followed by colony fission.

It is a host for the slave-maker.

Nomenclature

 *  difficilis. Formica rufa subsp. difficilis Emery, 1893i: 651, pl. 22, figs. 9, 14 (w.q.m.) U.S.A.
 * Wheeler, G.C. & Wheeler, J. 1953c: 164 (l.).
 * Status as species: Wheeler, W.M. 1904e: 305; Wheeler, W.M. 1904f: 348; Wheeler, W.M. 1906b: 16; Wheeler, W.M. 1913f: 477 (redescription); Cole, 1943a: 389; Creighton, 1950a: 500; Smith, D.R. 1979: 1462; Bolton, 1995b: 194; Coovert, 2005: 152; Ellison, et al. 2012: 151.
 * Senior synonym of consocians, habrogyna: Cole, 1943a: 389.
 * consocians. Formica difficilis var. consocians Wheeler, W.M. 1904f: 371 (w.q.m.) U.S.A.
 * Subspecies of difficilis: Wheeler, W.M. 1906b: 16; Wheeler, W.M. 1913f: 479 (redescription); Wheeler, W.M. 1916m: 597.
 * Junior synonym of difficilis: Cole, 1943a: 389.
 * habrogyna. Formica habrogyna Cole, 1939: 413, figs. A-D (w.q.) U.S.A.
 * Junior synonym of difficilis: Cole, 1943a: 389.