Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Costa Rica (southern Atlantic slope), Guatemala, Mexico (Chiapas).
Face nearly smooth, shagreened (not shiny), with 1-3 pairs of erect setae on face; mesosomal and gastral dorsa completely lacking erect setae; color dark red brown; HW 0.81 (n=1).
Similar species: Octostruma JTL-006.
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 lowland wet forest.
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.
Rhopalothrix (Octostruma) wheeleri Mann 1922:43. Holotype worker: Guatemala, Livingstone [USNM].
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.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.email@example.com
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