Attini, Myrmicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica (type locality), Colombia, Venezuela, Guyana, Brazil, Peru, Bolivia (Lattke 1997).
Identification
Metanotum lacking longitudinal carinae; anterior margin of clypeus convex, with thin fringe of smooth cuticle; mesosoma length about 1.8mm or greater; scape index (scape length/head width) about 1.5; frontal lobes in face view appear grossly swollen and rounded.
Similar species: Apterostigma collare has less inflated frontal lobes and relatively longer scapes.
Natural History
Apterostigma robustum inhabits wet forest habitats throughout the country, from sea level to 900m elevation. Foragers can be collected both during the day and at night.
Nests are exposed on tree trunks, or more often sheltered in cavities in rotten logs, suspended dead branches, or dead stilt palm roots. When exposed on tree trunks, the form of the nest is very like collare, with a white hyphal sack enveloping the nest. However, the sack is often (always?) covered with a layer of small wood fragments and other debris, which makes it very cryptic. When sheltered in a cavity the sack may be lacking. Nests tend to be larger and contain more workers than collare.
At La Selva Biological Station I observed a nocturnal foraging column leading to a nest. A line of workers was carrying clumps of slimemold(?) fruiting bodies (click here for image). The line extended from a 30cm long patch of these fruiting bodies, 2m across a rotten log, and into a 5cm diameter chamber in the rotten log. The chamber was filled with the fungus garden, which was suspended from the ceiling of the chamber. The garden was fluted and and looked like stalactites. The slimemold fruiting bodies were distributed evenly throughout the garden. The fruiting bodies were pure white, like polished rice, about 5mm long, and extremely delicate. They disintegrated into a milky liquid at the slightest touch.
In the Pe–as Blancas Valley east of Monteverde, I found a nest in a crevice in the undersurface of a rotten log, about 2m high. The nest had an outer covering of accreted particles of rotten wood, in the same shape as a typical Apterostigma collare nest. The collection contained a single bit of insect chitin (a beetle pronotum?) along with wood debris.
I have twice found small founding colonies; both were monogynous. One was under an epiphyte mat in an old treefall, and one was under loose bark on a rotten log.
Literature Cited
Emery, C. 1896. Studi sulle formiche della fauna neotropica. XVII-XXV. Bull. Soc. Entomol. Ital. 28:33-107.
Lattke, J. E. 1997. Revisi—n del gˇnero Apterostigma Mayr (Hymenoptera: Formicidae). Arq. Zool. (S‹o Paulo) 34:121-221.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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