Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae) Author Ward, Philip S. text Journal of Hymenoptera Research 1993 2 117 168 journal article 10.5281/zenodo.10150 2958 Pseudomyrmex nigropilosus ( Emery 1890 ) (Fig. 7) Pseudomyrma nigropilosa Emery 1890:62 . Syntype workers , Liberia , Costa Rica ( A. Alfaro ) ( MCSN , MHNG ) [Examined] , Pseudomyrmex nigropilosus (Emery) ; Kempf 1958:453 . Worker diagnosis. With the traits of the P. gracilis group (see couplet 6 of key) and the following more specific features. Head longer than broad (Cl 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 ( PLI 0.69- 0.77) with a short anterior peduncle (Fig. 7, 53); 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. Taxonomic comments. - Among the Pseudomyrmex species recorded from swollen-thom acacias, P. nigropilosus is easily identified by its elongate eyes and head ( REL 0.55-0.59, Cl 0.84- 0.90), short petiole ( PLI 0.69-0.77), and conspicuous black pilosity (Fig. 7). Kempf (1958) provides further descriptive details. Distribution and biology. - P. nigropilosus is found from Nayarit, western Mexico to Guanacaste Province, Costa Rica, and is restricted to nesting in swollen-thom 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. Additional information about the ecology of this species is given in Janzen (1975) .