Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica (southern Atlantic slope).
Identification
Face nearly smooth, shagreened, not shiny, with one pair of erect setae near middle of face; mesosomal and gastral dorsa completely lacking erect setae; color dark red brown; HW 0.81 (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.
I know this species from one specimen from a Winkler sample, Hitoy Cerere Biological Reserve at 200m, a wet forest site.
Taxonomic notes
Mann (1922) described the species wheeleri from a single specimen from Guatemala. Brown and Kempf (1960) redescribed the worker as follows:
The worker holotype was examined and measured ... TL 3.0, HL 0.64, HW 0.71 (CI 111), WL 0.78 mm.Habitus of head much as in O. jheringi; sculpture, though irregularly rugulose-punctate, less rugged than in jheringi, and not forming longitudinal costulae. Posterior occipital surface and most of alitrunk smooth but very finely shagreened and opaque to subopaque. Gaster densely punctate. Alitrunk convex in profile, without longitudinal sulcus; propodeal dorsum sloping posteriad; propodeal teeth triangular. Six erect clavate hairs on cephalic dorsum: one pair far up on the verticocciput, one hair on each side of the occipital lobes posteriorly and one hair on each side near the eyes. No other prominent erect hairs on body. Numerous fine, short appressed hairs on head, dorsum of alitrunk, both nodes and gaster. Color reddish-brown.
A single badly rubbed specimen labeled "Tres Rios, C. Rica", collected by A. Bierig and in the Borgmeier Collection, is similar to the wheeleri holotype and is probably the same species, though it has not been compared directly with the type. TL 3.2, HL 0.72, HW 0.78 (CI 108), WL 0.80 mm. This worker has a very feebly marked metanotal groove.
The description of wheeleri is similar to JTL-006, with which it may prove conspecific, and the Costa Rican worker matches JTL-007.
Rhopalothrix (Octostruma) wheeleri Mann 1922:43. Holotype worker: Guatemala, Livingstone [USNM].
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.
Mann, W. M. 1922. Ants from Honduras and Guatemala. Proc. U. S. Natl. Mus. 61:1-54.
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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