Pseudomyrmex capillatus

Pseudomyrmex capillatus is thus far known only from Jalisco and Colima in western Mexico. In tropical dry forest at Estación Biología Chamela two nest series were collected by P.S.Ward, both in dead twigs of vines (the vines were 1 m apart, so the nests were likely part of a single colony), and a worker was collected foraging on low vegetation. Recorded elevations are 100 m and 365 m.

Identification
Medium-sized species (HW 0.99–1.07) with moderately elongate head (CI 0.81–0.84) and eyes (see REL and REL2 values); frontal carinae separated by slightly less than basal scape width; metanotal groove distinctly impressed; dorsal face of propodeum flat, elevated anteriorly above level of mesonotum, rounding into declivitous face, the two faces subequal in length; petiole relatively slender (PLI 0.54–0.57, PL/HL 0.54–0.56), in profile petiole with a slight anterior peduncle and with flat to convex anterodorsal face, ascending gradually to summit in the posterior half of node, then rounding into more rapidly descending posterior face; profemur slender; hind leg relatively short (LHT/HL 0.70–0.72). Head opaque, densely coriarious to coriarious-imbricate, punctulae very fine and inconspicuous. Standing pilosity common on head, mesosoma (including mesonotum and propodeum), petiole, postpetiole, and gaster (MSC 25–39, HTC 0, MTC 1–2). Body rather uniformly dark-brown, except scapes, mandibles, anterior quarter of head capsule, protibia, and protarsus, which are a contrasting light yellowish-brown.

This species is notable for the conspicuous standing pilosity that covers the entire mesosoma dorsum (Fig. 13). Such pilosity is generally restricted to 1–3 pairs of setae on the worker pronotum in other members of the P. elongatulus group. Other salient features of the P. capillatus worker are the densely sculptured and opaque head, raised dorsal face of the propodeum, and unique color pattern (see Worker Diagnosis). Surprisingly, our UCE analyses show P. capillatus to be embedded phylogenetically within Pseudomyrmex arcanus (Fig. 1), although the two are superficially quite different in appearance. Both species occur sympatrically at Estación Biología Chamela, the type locality of P. capillatus, but the Chamela sample of P. arcanus (D1651) is not sister to the two P. capillatus samples. This suggests that P. arcanus, the more widespread of the two species, is in the process of achieving allelic monophyly relative to P. capillatus, but that this has not yet gone to completion.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Nomenclature

 * . Pseudomyrmex capillatus Ward & Branstetter, 2022: 19, figs. 13, 22 (w.) MEXICO (Jalisco).

Type Material

 * Holotype Worker. MEXICO Jalisco: Est. Biología Chamela, 100 m, 19° 30′ N 105° 02′ W, 18 Dec 1987, ex dead twig of thorny vine, tropical dry forest, P. S. Ward PSW09248 (UNAM) (CASENT0863535).
 * Paratypes: series of workers, same data as holotype (CASC, CZUG, IEXA, MCZC, PSWC, UCDC, USNM).