Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica (widespread in mid-elevation moist to wet forest).
Identification
Face longitudinally rugose; face usually with 10 and mesosoma usually with 4 erect spatulate setae; first gastral tergite usually with 4 erect spatulate setae; first gastral tergite punctate anteriorly, grading rather abruptly to nearly smooth and shining posteriorly (puncta becoming dense again at posterior border on some specimens); color red brown; HW 0.64 (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 is apparently rare (either low density or not easily sampled) but widespread. I know it from one Winkler sample from each of the following five localities: Rio Penas Blancas at 800m, Estacion Biologica Pitilla at 700m in Guanacaste Conservation Area, Reserva Biologica Carara at 500m, C.A.T.I.E. near Turrialba at 550m, and Reserva Biologica Hitoy Cerere at 200m.
Taxonomic notes
This species has a weak longitudinal trough on the mesosoma, and thus would key to iheringi in Brown and Kempf's revision. Brown and Kempf would certainly have included it within their polytypic concept of iheringi.
Kempf and Brown synonymized a number of forms under iheringi. With the splitting of iheringi into several forms, those synonyms will need to be reevaluated. In particular, the type of godmani should be examined (see synonymy under iheringi).
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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