Trachymyrmex nogalensis Byars 1951

T. nogalensis Byars

Trachymyrmex nogalensis Byars, 1951: 109. Holotype worker; Nogales, Arizona, U.S.A. (USNM) [examined]; Paratype workers, same locality (AMNH, MCZC, USNM) [examined].

Diagnosis

Worker: HL 1.1-1.35, HW 1.05-1.5, CI 96-112, SL 1.4-1.8, SI 117-133, ML 1.7-2.2. Large species (HL 1.1-1.35; HW 1.05-1.5), with relatively long legs and antennae (SI 117-133). Head generally longer than broad (CI 96-112), tapering slightly anterior to the eye, posterior border weakly concave. Antennal scape narrowing abruptly toward the antennal insertion, with a conspicuous lobe just distal to the narrowing. Frontal lobes well developed, evenly rounded, equilateral. Frontal carinae short, joining with preocular carinae to form short, distinctive "scrobes" that end just posterior to the level of the eye. Anterior terminus of the preocular carina forming a small tooth in full-face view. Anterolateral promesonotal teeth spinelike, sharply pointed, directed upwards and forward in side view. Propodeal spines toothlike, shorter than the distance between their bases. Body moderately tuberculate. Color yellowish brown.

Queen: HL 1.36-1.45, HW 1.4-1.45, CI 97-104, SL 1.64-1.8, SI 117-124, ML 2.25-2.4. Generally as in worker diagnosis, but mesosoma with caste-specific morphology relating to wing-bearing and the head bearing small ocelli. Dorsolateral pronotal teeth large, tuberculate and sharply pointed in dorsal view; ventrolateral pronotal teeth well-developed, resembling a blunt lobe. Mesoscutum lacking longitudinal rugulae but with numerous small tubercles, each bearing a short, sharply recurved seta.

Male: unknown.

Discussion

Trachymyrmex nogalensis is distinguished from other US Trachymyrmex species by the short, unique "scrobes" and the unusual basal lobe on the antennal scapes. In the field it can be confused only with the occasionally sympatric T. arizonensis, from which it is easily distinguished by the basal lobe on the antennal scape, (absent in T. arizonensis), and the distinctive frontal lobes of T. arizonensis (Figure 1B), (absent in T. nogalensis).

Etymology

Trachymyrmex nogalensis was described from Nogales, Arizona, based on workers that Byars collected from a colony nesting under his house. The species name clearly refers to the type locality.

Biology

Trachymyrmex nogalensis is rarely collected and is also the only Trachymyrmex species in the US whose male remains undiscovered. So far, it is known from only two locations in Arizona: the type locality, Nogales (in Santa Cruz County) and the Chiricahua Mountains (Cochise County) in the southeast corner of the state. All collections have been made in mid elevation habitats at 1200-1550 m.

Byars (1951) collected workers and dealate queens on the porch of his house. Unfortunately, he provided no further information on the surrounding habitat or on any other nests. In the Chiricahua Mountains, we found T nogalensis in creosote bush, mesquite-dominated desert habitats and on a rocky limestone outcrop dominated by Ocotillo, Acacia, Agave and Mimosa. Nests were cryptic and the entrances were located in cracks on rock-face. No information is available on nest architecture, fungus gardens, or number of workers in a colony because the extremely rocky ground makes excavation close to impossible. Trachymyrmex nogalensis is seldom encountered, probably because of it nocturnal foraging behavior and its cryptic nest sites. Studies of ecology, behavior and fungus cultivation would be fruitful areas for further research.

Additional material examined: U.S.A.: Arizona, Cochise County: Chiricahua Mtns. 0.8mi WNW Jct. FSR 42 on FSR42D (SP Cover), Chiricahua Mtns. 2km WNW Portal (G Alpert, RA Johnson, C Rabeling), Huachuca Mtns., Palmerlee (WM Wheeler); Santa Cruz County: Nogales (JN Kaiser, J Steward).