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Widespread in Neotropics, from southern Mexico to Argentina. Costa Rica: throughout the country from sea level to 1700m.
Apterostigma pilosum, almost certainly a complex of many species (see Comments), occurs in forested habitats throughout Costa Rica, from sea level to cloud forest habitats at 1700m. Most examples are workers and queens extracted from Berlese or Winkler samples of sifted leaf litter. In the Bosque Humedo of Santa Rosa National Park I found a nest under a stone. The fungus garden was a spongy mass about 5cm wide. The colony was polygynous, with at least 9 dealate queens. At Estacion Pitilla in the Guanacaste Conservation Area, I found a golf ball-sized nest under rotten wood along a dirt road in second growth forest. At the El Ceibo station along the Barva Transect in Braulio Carrillo National Park, I found a nest under dead wood on ground. The nest space was a disk-shaped area about 4cm across. White hyphae lined the nest and the center was a mass of fuzzy yellow particles. The workers were all immobile on disturbance and very hard to see. They remained motionless for several minutes before beginning to move.
Lattke (1997) discussed the pilosum complex as a variable group within which species boundaries were uncertain. He did not attempt to revise the group but instead highlighted the need for further research. After examining 37 different collections from 23 localities in Costa Rica, I conclude that the same complexity occurs within Costa Rica. These are the most generalized and smallest Apterostigma. They vary in size, scape index, and shape of frontal lobes, but I have not been able to sort them into discrete morphological clusters. Almost all the collections are from workers in samples of sifted leaf litter from the forest floor, so there are few observations of behavior or nest structure that might point to species differences. Given the nature of diversity and the amount of morphological variation, I am almost certain this group is comprised of numerous species. Lattke lists numerous available names in the pilosum complex, but for now I call them all pilosum (the oldest name in the group) until we know more about species boundaries.
Lattke, J. E. 1997. Revisi—n del gŽnero Apterostigma Mayr (Hymenoptera: Formicidae). Arq. Zool. (S‹o Paulo) 34:121-221.
Alto Paraguay, Alto Paraná, Amambay, Canindeyú, Concepción, Itapúa, Misiones (ALWC, INBP, LACM, MHNG USNM). Literature records: Alto Paraná (Fowler 1981).
Found most commonly in these habitats: 3 times found in Plateau, 1 times found in Grassland, 1 times found in Forêt sommitale Inselberg.
Found most commonly in these microhabitats: 4 times Leaf litter, 1 times Foraging ants.
Collected most commonly using these methods: 4 times Winkler48h.
Elevations: collected from 99 - 600 meters, 429 meters average