Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica (Atlantic lowland rainforest, Osa Peninsula rainforest).
Identification
Face with 8-12 erect clavate setae; mesosoma usually with 2 pairs erect clavate setae; first gastral tergite with up to 16 erect spatulate setae; face, mesosomal dorsum, petiolar node, postpetiole, and gastral dorsum covered with conspicuous, curved, clavate, subdecumbent ground pilosity; ground pilosity often binding a uniform layer of soil over entire face, mesosoma, and gaster; vertex lobes (when visible) uniformly punctate and opaque; color orange; HW 0.72 (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.
At La Selva Biological Station, this species is known from three collections: one of the Project ALAS Berlese samples, a stray worker collected from the ground by Louisa Stark, and a nest series that I collected. The nest was a 2-3cm dia. cavity beneath a rotten pejibaye trunk lying on bare soil, in an open second growth area. I collected the entire nest contents as far as I could tell; it contained 139 adult workers, 4 dealate queens, 1 alate queen, and abundant brood including worker, male, and queen pupae, and larvae of all sizes. I also have collected this species in Winkler samples from other sites, one from C.A.T.I.E. near Turrialba, and one from Corcovado National Park on the Osa Peninsula.
This species presents an extreme of camouflaging behavior. The isolated workers of this species (not the ones from the nest collection) have a thick adherent soil layer over the entire dorsal surface of the body, including the face, mesosoma, and gaster. Although some other Octostruma species also accumulate a soil layer, it tends to be concentrated on the face and less often on the mesosoma. JTL-004 is the only species I know that also develops a thick soil layer on the gaster.
Taxonomic notes
This species is clearly not any of those treated in Brown and Kempf's revision.
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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