Acanthostichus texanus

SPECIES NAME: Acanthostichus texanus Forel

TAXONOMIC SUMMARY:

DIAGNOSIS: All three castes of this species are easily distinguished from those of the other species. The workers are easily distinguished from all other known species by the relatively large eye and the top of the petiole is smooth and strongly shining (found in few other species). Workers of A. emmae would be expected to have a more quadrate petiole than those of A. texanus, but would otherwise be expected to be similar. The female is easily distinguished as it is one of the few in the genus that would have wings. They are not subdichthadiiform as in other species and are actually very similar to the workers, both in size and form. The top of the petiole is smooth and the petiole is elongate. The female is similar to that of A. emmae, but has a narrower head, narrower petiole and smaller ocelli and is thus easily separated. The male is similar to those of other species in the genus, except for the genitalia, which are very distinct, and it has a 13 segmented antenna. The teeth of the subgenital plate are thickened, which easily and conveniently separates this species from all other known males. The males of A. emmae would be expected to be similar, but may have petiolar nodes much more quadrate than those of A. texanus. The males of A. texanus have not been associated with workers, but these three castes are probably all members of the same species. All three castes are quite different from those of other species, it is the only species collected from the area around Monterrey, Mexico, and the petioles of the three castes are polished and shining. There is little doubt they are conspecific. Males have petioles of two forms, but are assumed to be a single species.

BIOLOGY: This species is primarily subterranean and preys on termites (Gnathamitemrmes tubiformans). One method of finding workers involves looking under cow manure pats, where they may be preying on termites. Workers have most commonly been found in the autumn and winter (October through December). Two males were collected in May and November 1987 at 13:30 (D. Gonzalez, pers. comm.). Two workers were collected in the soil when D. Gonzalez was excavating a Pogonomyrmex barbatus nest (pers. comm.). [As reported in MacKay 1996]

DISTRIBUTION: Northeastern Mexico and southeastern Texas

DESCRIPTION:

Worker: HL 0.94 - 1.06, HW 0.83 - 0.96, SL 0.43 - 0.48, SW 0.15 - 0.18, EL 0.05 - 0.08, WL 1.39 - 1.56, FL 0.65 - 0.70, FW 0.28 - 0.33, PW  0.38 - 0.48, PL 0.48 - 0.54, SI 44 - 45, C186 - 93, PI 113 - 130, FI 2.15  - 2.36, SL/ SW 2.64 - 2.92. Mandibles without teeth, but angulate at apex; anterior border of clypeus notched, frontal carinae forming angles which extend past anterior medial border; vertex broadly concave, sides  nearly parallel, slightly convex; eyes relatively large, consisting of about  10 poorly defined ommatidia; anterior border of scape weakly concave; mesosoma similar to those of other members of the genus; propodeum not concave posteriorly, lacking spines or teeth; petiole wider posteriorly than anteriorly; subpetiolar process large, well developed, anterior edge broadly rounded, posterior edge broadly concave, faces meeting at distinct angle (Fig. 42); gaster as in other species, pygidium toothed. Hairs long (0.25 mm), erect, pointed and on all surfaces; entire ant devoid of decumbent pubescence. Dark reddish brown, smooth and polished throughout.

Queen: HL 0.95- 1.24, HW 0.84 - 1.03, SL 0.43 - 0.51, SW 0. 15 - 0. 19, EL 0.23 - 0.29, WL 1.65 - 1.88, PW 0.40 - 0.60, PL 0.53 - 0.64, SI 41 -  45, CI 83 - 88, PI 106 - 131, SL/SW 2.73 - 2.92. Mandible essentially toothless, except for very fine serration in one specimen; clypeus with very small lateral bumps; eyes large, reaching side of head  in full face view; ocelli small (diameter of median ocellus 0.06 mm);  scape very slightly concave anteriorly; sides of head nearly parallel; vertex slightly concave; mesosoma little modified for flight;  posterior face of propodeum concave; petiolar node elongate, widened  posteriorly, All surfaces with abundant erect hairs, decumbent pubescence limited to parts of mesonotum near base of wings, descending  face of propodeum and anterior face of petiole. Sculpture is shining and polished, color is dark reddish brown.

Male: (measurements of C. townsendi lectotype in parentheses): HL 0.83 - (0.85), HW (posterior to eye) (0.78) - 0.80, SL (0.24) - 0.28, SW (0.1) 0.1, EL (0.35) - 0.39, WL (1.79) - 1.85, PW (0.43) - 0.44, PL (0.49) - 0.54. Indices: SI (28) - 34, CI (92) - 96, PI (1 14) - 123. Mandible without teeth, apex angled; median anterior border of clypeus broadly convex; eyes large, convex; 3 well developed ocelli, diameter less than distance between them; antennae 13 segmented, sides of scape parallel, anterior edge not concave; vertex of head convex; posterior face of petiole broadly concave, petiole shaped as in worker, elongate, wider posteriorly, subpetiolar process shaped as in worker, but not as wide. Genitalia unusual for the genus. Parameres large with long slender shaft, hairy apex which is hook-like, pointed ventrally and posteriorly; aedeagus very distinctive, consists of elongate process which terminates in triangular shaped, toothed structure; volsellae large with round lobe; subgenital plate distinctive, terminating in two broad  teeth (Fig. 77). Hairs covering entire surface, most about 0.1 mm long, few up to 0.25 mm, lacking decumbent pubescence. Sculpture mostly smooth, shining, mandibles and head shagreened or finely punctate. Very dark brown in color, mandibles, funiculus, legs, genitalia lighter brown.

LITERATURE: MacKay, W. P. 1996. A revision of the ant genus Acanthostichus (Hymenoptera: Formicidae). Sociobiology 27:129-179.