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.
Costa Rica (type locality), Colombia, Venezuela, Guyana, Brazil, Peru, Bolivia (Lattke 1997).
Taxonomic history
Lattke, 1997 PDF: 168 (m.).Senior synonym of Apterostigma amiae: Weber, 1958d PDF: 249.Senior synonym of Apterostigma branneri: Weber, 1958d PDF: 249.Senior synonym of Apterostigma robustum constrictum: Weber, 1958d PDF: 249.Senior synonym of Apterostigma robustum tic: Weber, 1958d PDF: 249.See also: Lattke, 1997 PDF: 167.
