Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica (Cordillera de Tilar‡n above 700m), Mexico (Chiapas).
Identification
Face reticulate rugose; face with 8-12 erect clavate setae; mesosomal and gastral dorsa completely lacking erect setae (Costa Rica) or with pair of setae on mesosoma (Mexico); color dark red brown; HW 0.76 (n=1).
Natural History
The genus Octostruma is known only from the New World tropics, from southern Mexico and the West Indies to northern Argentina (Brown and Kempf 1960). It is a part of the "cryptobiotic" fauna: small, slow-moving ants that live in rotten wood and leaf litter. The very similar genus Eurhopalothrix is known to be predaceous on small, soft-bodied arthropods (Brown and Kempf 1960, Wilson 1956, Wilson and Brown 1985).
Workers and nests are extremely difficult to see in the field. Some species camouflage themselves with layers of soil (Hoelldobler and Wilson 1986). As a result of their cryptic nature, they were considered extremely rare until the 1960's. But increasing use of Winkler and Berlese sampling has shown Octostruma to be relatively common. I encounter them in most Winkler samples from wet forest sites in Costa Rica.
This species occurs in mid-montane wet to moist forest.
Comments
The Mexican specimens appear identical to the Costa Rican specimens except for the presence of a pair of erect setae on the mesosomal dorsum. This is an upland form of O. wheeleri. The only difference from O. wheeleri is the more reticulate rugose sculpture on the posterolateral vertex (instead of smooth) and a larger number of erect setae on the face and vertex margins (8-12 vs. 6). The highland vs. lowland separation of the two species holds in Costa Rica and Chiapas, Mexico.
Literature Cited
Brown, W. L., Jr., Kempf, W. W. 1960. A world revision of the ant tribe Basicerotini. Stud. Entomol. (n.s.) 3:161-250.
Hoelldobler, B., Wilson, E. O. 1986. Soil-binding pilosity and camouflage in ants of the tribes Basicerotini and Stegomyrmecini (Hymenoptera, Formicidae). Zoomorphology (Berl.) 106:12-20.
Wilson, E. O. 1956. Feeding behavior in the ant Rhopalothrix biroi Szabo. Psyche (Camb.) 63:21-23.
Wilson, E. O., Brown, W. L., Jr. 1985 ("1984"). Behavior of the cryptobiotic predaceous ant Eurhopalothrix heliscata, n. sp. (Hymenoptera: Formicidae: Basicerotini). Insectes Soc. 31:408-428.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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