Pseudomyrmex nigropilosus

An acacia nesting species, this ant is considered a parasite of the mutualism formed between acacias and other Pseudomyrmex species. Pseudomyrmex nigropilosus will use the hollow-thorn domatia and exploit the food produced by the plants, i.e, beltian bodies and nectar from extrafloral nectaries, but they are not effective at decreasing herbivores and do not remove encroaching vegetation.

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.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Mexico.

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].