Formicoxenus diversipilosus

This ant is a guest or xenobiont in the nest of Formica obscuripes. Workers obtain food from host workers during food tranfer within the nest. Nests are kept separate with Formicoxenus diversipilosus nesting within the hollow twigs and root clumps within the host nest.

Identification
F. diversipilosus can be distinguished from Formicoxenus hirticornis by the less compressed frontal region of the head, the proportionally broader petiolar peduncle, the differently shaped postpetiole and the narrower head.

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

Biology
Multiple nests of this inquiline can be found within the large thatch mound of its host,. Another similar inquiline ant also found within Formica obscuripes nests is Formicoxenus hirticornis. These ants have forms intermediate between workers or queens, known as intercastes. Foragers do not leave the nest but acquire food from their hosts as they exchange food. Mating occurs within the nest or on top of the nest mound. Males are worker-like, with larger eyes than workers and without wings.

Alpert and Akre (1973) - A field survey of the distribution of Formicoxenus diversipilosus in Washington was conducted from June 1970 to August 1971. Laboratory studies were conducted from October to January in 1969, 1970, and 1971. F. diversipilosus was previously considered a rare ant guest in the nest of its only known host, Formica obscuripes. F obscuripes nests were collected from the eight major physiographic areas in Washington and sorted in the laboratory. The inquiline was found in 30% of the nests sampled, and Formica ravida was established as a new host record. Only northwestern Washington yielded negative results, although 30 F. obscuripes nests were collected from this area. Throughout the remainder of the State, F. diversipilosus maintained the same range as its host, and it occurred under a wide variety of vegetative, climatic, altitudinal, and soil conditions.

Laboratory studies indicated that F. diversipilosus is a xenobiont in the nest of F. obscuripes. F. diversipilosus was never found living alone and was unable to survive without its host. Brood was reared separately from the host brood, although the adults moved freely throughout the host nest. F. obscuripes usually treats the inquiline with indifference and occasionally with slight hostility. However, observations indicated F. diversipilosus can obtain regurgitated food from their hosts either directly from a worker or more often from two workers as they exchanged food. Mating, transportation of adults and larvae, trophallaxis, grooming, and aggressive behavior are described.

Castes
Intermediates between workers and queens are common. Males are worker-like and wingless.

Nomenclature

 * . Leptothorax (Mychothorax) diversipilosus Smith, M.R. 1939c: 179 (w. ergatoid q.) U.S.A. (Washington).
 * Type-material: lectotype worker (by designation of Francoeur, Loiselle & Buschinger, 1985: 381), 1 paralectotype worker, 1 paralectotype ergatoid queen.
 * Type-locality: lectotype U.S.A.: Washington, Fort Lewis, 15.x.1938 (F. Smith); paralectotypes with same data.
 * Type-depository: USNM.
 * Smith, M.R. 1956c: 274 (ergatoid m., q.); Wheeler, G.C. & Wheeler, J. 1989a: 321 (l.).
 * Combination in Formicoxenus: Buschinger, 1979a: 61.
 * Status as species: Creighton, 1950a: 278; Smith, M.R. 1951a: 821; Smith, M.R. 1956c: 271; Smith, M.R. 1958c: 133; Yensen, et al. 1977: 183; Smith, D.R. 1979: 1396; Buschinger, 1981: 213; Francoeur, Loiselle & Buschinger, 1985: 381 (redescription); Wheeler, G.C. & Wheeler, J. 1986g: 51 (in key); Bolton. 1995b: 207; Ward, 2005: 32.
 * Distribution: U.S.A.

Worker
Length 2.6-2.8mm.

Head, exclusive of mandibles, almost one-fourth longer than broad, posterior border straight or very faintly emarginate, occipital angles feebly rounded, sides almost subparallel, very feebly divergent anteriorly; vertex without ocelli; dorsal surface of head not noticeably compressed on each side of frontal carinae as with hirticornis. Eye rather small, moderately convex, approximately twice its greatest diameter from base of mandible. Antenna 11-segmented; scape when fully extended not attaining posterior border of head, first funicular segment at least as long as combined lengths of the two preceding segments, and antennal club slightly longer than remainder of funiculus. Frontal area not clearly discernible. Clypeus prominent, anterior border broadly rounded, entire, posterior border extending well back between frontal carinae; dorsal surface faintly impressed medianly toward anterior border. Mandible with two large apical teeth and four small, nearly subequal teeth. Thorax from above distinctly broader anteriorly than posteriorly, with prominent transverse pronotal ridge, rounded humeral angles, and distinct but not so strong mesoepinotal constriction as with hirticornis; epinotal spines moderately acute, very short, not noticeably compressed. In profile, dorsum of thorax almost on same plane, with feebly convex, almost flattened surface; mesoepinotal constriction, although visible dorsally and laterally, much less pronounced than with hirticornis, base of propodeum less strongly convex. Petiolar peduncle from above almost square, only one-sixth longer than broad, sides parallel. In profile, anterior surface of node straight; posterior surface gently concave before meeting the postpetiole. Postpetiole broader than long, broader anteriorly than posteriorly, sides converging posteriorly, trapezoidal. Gaster similar to that of hirticornis.

Posterior border of clypeus, frontal area, an indefinite area on front, and gaster smooth and shining; scapes, head, thorax, legs excepting tarsi, petiole, and postpetiole finely and densely punctulate, subopaque. In addition, front of head and cheeks with very faint longitudinal rugulae.

Hairs short, erect, clave (almost capitate), present on dorsal surface of head, tips of femora, tibiae, and metatarsi; slender, tapering hairs on clypeus, mandibles, antennae, under side of head, thorax, coxae, trochanters, femora excepting tips, tarsi excepting metatarsi, petiole, postpetiole and gaster.

Dark ferruginous; base of gaster brown; eyes and mandibular teeth black. In some lights the body appears lighter than in others.

Queen
Ergatoid female. Length 3.1mm.

Differing from the worker as follows: Vertex with three small ocelli. Thorax from above with pronotum, scutum, scutellum, metanotum, epinotum, and all sutures except that separating the metanotum and epinotum faint; the two latter areas separated by a foveolated constriction that extends across dorsum and down on to each side of thorax. Entire clypeus and a large spot on front shining. Body much darker than that of worker, the petiole and postpetiole deeply infuscated. Gaster almost entirely black.

M. R. Smith (1956) - Dealate, Length 3-3.5 mm.

Similar to the worker except for the following: Larger, stouter and more deeply colored. Eye larger and more convex. Thorax with the usual sclerites typical of a femaie (queen); viewed from above, with prominent but rounded humeral angles and a distinct constriction or concavity on each side of the body anterior to the insertions of the front pair of wings.

Male
M. R. Smith (1956) – Ergatoid, Length 2.5-2.75 mm.

Head, excluding mandibles, approximately one-sixth longer than broad, with straight or feebly rounded posterior border, rounded posterior corners and convex sides behind the eyes; sides anterior to eyes converging anteriorly, thus giving the area in the vicinity of the mandibles a narrow, reduced appearance. Eye larger and more convex than that of the worker. Antenna 12-segmented; scape noticeably enlarged toward the apex, not attaining the posterior border of the head; funiculus more slender than that of the worker, the segments progressively enlarged apically but without forming a clearly differentiated club, the three segments preceding the last subequal in length. Clypeus prominent, strongly convex, protruding above and beyond the mandible and partly concealing them; the anterior and posterior borders rounded, the posterior border more rounded than the anterior and extending well between the frontal carinae. Mandible greatly reduced; masticatory margin with a long apical and several small, indistinct teeth. Vertex of head with small, indistinct ocelli. Frontal area poorly defined. Thorax, petiole, and postpetiole similar to that of the worker but more slender. Promesonotal suture obsolete. Postpetiole more convex dorsally than that of the worker. Gaster similar to that of worker, when viewed from above, with the first segment occupying almost all of the dorsal surface; genitalia concealed.

Hairs moderately abundant, simple, grayish, short, suberect to erect; some of the hairs on the head and appendages appear to be a little thicker than those on the remainder of the body and to assume a slightly clavate form, especially a small number on the vertex of the head. Hairs at apex of gaster the longest.

Head, thorax, petiole and postpetiole punctate, subopaque; scape, femur and tibia more finely punctate, almost shining in certain lights. Most of the clypeus, frontal area, a median line or spot on front of the head, and gaster, smooth an shining.

Color dirty ferruginous, lighter than that of the worker; gaster dark brown, almost black.

Type Material
Cotype locality. Fort Lewis, Washington, October 15, 1938 (Falconer Smith). Cotypes. No. 53284, United States National Museum. Described from two workers and a single ergatoid female collected from the nest of the Western mound-thatching ant (Formica rufa subsp. obscuripes var. melanotica Emery). According to Falconer Smith, the nest of the host ant was found in the humid Transition Zone at approximately sea level. The vegetation in the vicinity was dominated by Douglas fir trees and low grass of the genus Poa and the areas immediately surrounding the nest was covered by a layer of moss, Eurynchium oregonum.

References based on Global Ant Biodiversity Informatics

 * Alpert G. D., and R. D. Akre. 1973. Distribution, abundance, and behavior of the inquiline ant Leptothorax diversipilosus. Annals of the Entomological Society of America 66: 753-760.
 * Longino, J.T. 2010. Personal Communication. Longino Collection Database