Pseudomyrmex nigropilosus

Identification
Ward (1993) - Among the Pseudomyrmex species recorded from swollen-thorn acacias, P. nigropilosus is easily identified by its elongate eyes and head (REL 0.55-0.59, CI 0.84-0.90), short petiole (PU 0.69-0.77), and conspicuous black pilosity.

Distribution
Western Mexico to Costa Rica.

This taxon was described from Costa Rica.

Biology
Ward (1993) - Restricted to nesting in swollen-thorn acacias (including Acacia collinsii, A. cornigera and A. hindsii). It is a member of the P. gracilis group and therefore not closely related to the principal group of acacia-ants (P. ferrugineus group). Janzen (1975) points out that P. nigropilosus is essentially a parasite of the Pseudomyrmex/Acacia mutualism. It occupies abandoned or otherwise uninhabited plants and reaps the benefits of this association without protecting the acacia from herbivores or competing plants.

Nomenclature

 *  nigropilosus. Pseudomyrma nigropilosa Emery, 1890b: 62, pl. 5, fig. 24 (w.) COSTA RICA. [Also described as new by Emery, 1894k: 51.] Combination in Pseudomyrmex: Kempf, 1958f: 453. See also: Ward, 1993: 159.

Description
Ward (1993) - With the traits of the P. gracilis group (see couplet 6 of key) and the following more specific features. Head longer than broad (CI 0.84-0.90); anterior margin of median clypeal lobe convex, conspicuously protruding; dorsolateral margination of pronotum usually blunt; mesonotum more steeply inclined than basal face of propodeum; petiole relatively robust (PU 0.69- 0.77) with a short anterior peduncle; head and mesosoma densely punctulate to coriarious-imbricate, and subopaque; standing pilosity conspicuous on most of the body including the outer faces of the tibiae, consisting largely of black hairs, those on the petiole and Propodeum long (> 0.20 mm) and curved. Color varying from concolorous orange-brown to bicolored orange and black to (western Mexico) predominantly black with orange mottling on the head, mesosoma, and appendages.

Type Material
Ward (1993) - Syntype workers, Liberia, Costa Rica (A. Alfaro) [Examined].