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Ants of tropical wet forests are common, yet practically unstudied, despite their importance in nutrient cycling and seed bank dynamics. I investigated the ecology of a leaf litter assemblage of twig-dwelling ants in lowland tropical wet forest and contrasted it with the better known ecologies of ground- and tree-dwelling ants. Nest densities at La Selva, Costa Rica were high (7.48 nests/m2) and potential nest sites were abundant. Colonies moved frequently (residence times for species ranged from 35 to 146 days) from one twig nest to another, occupying a wide range of twig types. Experiments with artificial nests showed that colonization was not reduced by the presence of resident ant colonies. Queenright nests (in which at least one queen is present) and queenless workers, as well as dealate queens, colonized artificial nests. Activity times and diet composition did not differ between the two species with largest sample sizes; workers were active under most conditions. Despite their abundance, twig-dwelling ants are apparently limited neither by availability of nest sites nor food. Many of the 32 species found coexisting at La Selva may be limited by high mortality during alate dispersal or colony movement.