Plants: Acacia (Leguminosae or Fabaceae)

swollen stipular thorns
extrafloral nectaries (EFN)
Beltian bodies
A. cornigera: canoe-shaped EFN; indehiscent seed pods; mesic habitats
A. collinsii: dome-shaped EFN; dehiscent seed pods; drier habitats

Ants: Pseudomyrmex (Formicidae)

nest-site selection (all)
host-restricted foraging (all?)
aggressive defense of extranidal territory (some)
nocturnal patrolling (some)
vegetation pruning (some)

Ward 1989Janzen
P. ferrugineus (Smith 1877) P. ferruginea
P. spinicola (Emery 1890) P. ferruginea
P. flavicornis (Smith 1877) P. belti (Emery 1890)
P. nigrocinctus (Emery 1890) P. nigrocincta
P. nigropilosus (Emery 1890) P. nigropilosa
P. subtilissimus (Emery 1890)

P. ferrugineus group
P. ferrugineus: Mexico to Honduras; red color; aggressive defender; basal pruning.
P. spinicola: Honduras to Colombia; red color; aggressive defender; basal pruning.
P. flavicornis: Mexico to Costa Rica; black color; aggressive defender; no basal pruning.
P. nigrocinctus: Mexico to Costa Rica; orange color; smaller than above spp.; aggressive defender; pruning?

Unrelated species
P. nigropilosus: Mexico to Costa Rica; orange color; larger than above spp.; timid non-defender; no pruning; known parasite (Janzen 1975).
P. subtilissimus: Nicaragua and Costa Rica; tiny, much smaller than above spp., with long thin head; gray-brown color; timid non-defender; obligate associate of P. flavicornis? Inquiline? (Ward 1989).

Janzen, D. H. 1966. Coevolution between ants and acacias in Central America. Evolution 20:249-272.

Janzen, D. H. 1975. Pseudomyrmex nigropilosa: A parasite of a mutualism. Science 188:936-937.

Janzen, D. H. 1983. pg. 762 in Costa Rican Natural History.

Ward, P. S. 1989. Systematic studies on pseudomyrmicine ants: revision of the Pseudomyrmex oculatus and P. subtilissimus groups, with taxonomic comments on other species. Quaestiones Entomologicae 25:393-468.

Ward, P. S. 1993. Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae). Journal of Hymenoptera Research 2:117-168.