Temnothorax mexicanus

The type series was collected nesting under a rock in a pine forest on a west-facing slope, covered with abundant rocks.

Identification
Mackay (2000) "This is a small, black species, with a smooth and strongly shining head, 12 segmented antenna, and very poorly developed propodeal spines (simple bumps). The dorsum of the pronotum and of the mesonotum are mostly smooth and polished. The dorsal face of the propodeum is punctate with transverse striae. The petiolar node is blunt and rounded. The female is considerably different from the worker as it is more heavily sculptured, has well-developed propodeal spines, and the node of the petiole is more acute.

The smooth, shining dorsum of the head with very fine striae differentiates this species from most of the others in the subgenus. The glossy pronotum and mesonotum will further distinguish this species from most others. Additionally the blunt petiolar node will separate it from other similar species, such as ''T. mariposa. T. melinus. T. nitens. T. adustus and T. chandleri it would be most likely to be confused with T. cokendolpheri and T. punctithorax''. The smooth dorsal surface of the postpetiole would separate it from both of these species, which have the dorsum of the postpetiole punctate. Note that the posterior surface of the postpetiole of T. mexicanus is punctate. Leptothorax mexicanus and T. punctithorax are both dark brown, but differ in the sculpture of the top of the postpetiole, and the dorsum of the mesonotum is nearly smooth and shining (with foveolate punctures in T. punctithorax). It could be confused with T. brevispinosus, from which it can be distinguished as the side of the pronotum is covered with striae (mostly smooth and glossy in T. brevispinosus). The sexuals of the two species arc distinct (see key to the tricarinatus species complex)."

Distribution
MEXICO. Coahuila and San Luis Potosi

Habitat
From pine forest through pinyon pine scrub.

Abundance
Uncommon.

Biology
Mackay (2000) - The type series was collected nesting under a rock in a pine forest on a west-facing slope, covered with abundant rocks. The specimen collected near San Luis Potosi was together with Pheidole sp., nesting in the soil in a mesquite/Yucca sp. scrub. with fine textured soils. The second series from Coahuila was under a stone, which was part of a rock wall. The soil was very rocky clay on a south facing slope. The vegetation consisted of dry scrub of pinyon pine, Yucca sp., etc. It was an open area with lots of stones and an abundance of interesting ants (Formica, Lasius, Camponotus, Monomorium, Liometopum, Pheidole, Myrmica).

Worker
Mandibles with 5-6 teeth, only 3 or 4 well defined; anterior border of clypeus moderately convex, clypeus mostly smooth and shining with poorly developed carinae and a median carina; head with weakly convex sides, vertex concave; eyes small, but exceeding sides of head; scape not reaching occipital corner; pronotum with promesonotal suture visible when seen from above, but none of sutures impressed with mesosoma in profile; propodeum with dorsal and posterior face equal in length, propodeal spines consisting of poorly developed angles; petiole with weakly concave anterior face, posterior face convex, petiolar node rounded in profile.

All surfaces with scattered, coarse, blunt hairs, hairs on legs and antennae (including scapes) much finer and semierect; decumbent pubescence nearly absent, except for a few coarse hairs on gaster.

Sculpture mostly smooth and shining, head with barely perceptible fine costulae on sides and dorsum of head, malar area with scattered punctures and fine rugae, mesopleuron and sides and faces of propodeum with scattered punctures, sides and part of tops of petiole and postpetiole with fine punctures, gaster shining. Color: dark brown.

Worker measurements: HL 0.60-0.65. HW 0.52-0.53. SL 0.49-0.52. EL 0.13-0.16. WL 0.70-0.72. PW 0.16-0.18. PL 0.20-0.22. PPW 0.19-0.22. PPL 0.16-0.17. Indices: CI 82-87. SI 80-82. PI 80-82. PPI 119-129.

Queen
Mandible with 5 or 6 teeth, only 3 or 4 are well defined; clypeus shining, with medial carina and several lateral carinae; clypeal border slightly concave; eyes large, extending past sides of head; ocelli well developed; scape extending slightly past posterior corners of head; vertex straight; propodeal spines large and well developed; petiole with nearly straight anterior and posterior faces, petiolar node sharply angulate.

Erect hairs abundant on most surfaces, mostly with sharpened ends, legs and antennae with semierect hairs; decumbent pubescence consisting of long, scattered hairs on gaster. Sculpture much more coarse than in worker, head with fine rugae, those between eye and mandible in form of semicircle, with center at point of insertion of antennae, much of mesosoma smooth and shining, sides of mesosoma strongly polished, propodeum with rugae which converge on tip of propodeal spines, sides of petiole and postpetiole shining, but with a few fine rugae and scattered punctures, gaster completely smooth and shining.

Concolorous dark brown.

Female measurements: HL 0.79-0.90, HW 0.77-0.82, SL 0.59-0.62, EL 0.22-0.23, WL 1.31-1.39, PW 0.22-0.25, PL 0.25-0.30, PPW 0.36-0.38, PPL 0.19-0.20, Indices: CI 91-97, SI 66-78, PI 73-100, PPI I89-190.

Male
Mandible with apical and subapical teeth defined, others present as small denticles; medial anterior border of clypeus nearly straight (slightly convex), clypeus with transverse rugae; eyes large; ocelli well developed; scape short; propodeal spines or angles absent; petiole with convex anterior face, posterior face convex, but broadly curving into posterior collar, petiolar node blunt and rounded.

Hairs erect and scattered on most surfaces, suberect on antennae and legs; decumbent pubescence sparse and only on gaster, consisting of long hairs.

Sculpture consisting of dense punctures on head, transverse rugae on anterior of clypeus, sides of mesosoma mostly smooth and shining, propodeum with scattered punctures on most surfaces, petiole and postpetiole mostly smooth and shining, gaster completely smooth and shining.

Color: dark concolorous brown.

Male measurements: HL 0.44-0.49, HW 0.44-0.46, SL 0.10-0.11, EL 0.19-0.20, WL 0.88-0.90, PW 0.11-0.13, PL 0.14-0.18, PPW 0.17-0.19, PPL 0.14-0.15. Indices: CI 94-100, SI 22-23. PI 72-79. PPI 121-127.

Type Material
Holotype worker (MCZC), 12 paratype workers, 12 paratype females and 21 paratype males (AMNH, CASC, CWEM, FMNH, LACM, MCZC, USNM, UNAM)

Type Locality Information
MEXICO, Coahuila, 16 KE San Antonio, 20 May 1988, W. Mackay #10270, nest collected under rock.

Etymology
Toponym. "Based on wide distribution in northeastern Mexico."