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Trachymyrmex is a taxonomically difficult group of inconspicuous attines, all of which are monomorphic and with tuberculate gaster. Most or all of the Costa Rican species nest in the soil, with 5-10cm diameter spherical chambers located within 20cm of the surface (at least in wet forest habitats). Colony sizes are usually small, a few hundred workers or less. The solitary foragers are inconspicuous and often freeze when disturbed, making it difficult to discover them in the field. In many species the nest entrance is completely unadorned, a simple tiny hole in the soil. They are fairly abundant in most lowland and mid-elevation habitats, but mass sampling methods such as Winkler sifting, Berlese extraction, Malaise traps, and Canopy fogging only rarely capture workers. Direct visual search and manual collecting is probably the most efficient way to discover them. A light-colored bait such as cracked barley may be harvested by Trachymyrmex workers, which then allows you to follow workers to nest entrances. Workers harvest a wide variety of materials as fungus substrate, including caterpillar droppings and occasionally cut leaves.
Recent taxonomic work on the genus has been carried out by Mayh-Nunes and Brandao (2002, 2005, 2007).
The following are taxa that should be checked for matches with Costa Rica morphospecies:
Atta (Acromyrmex) tardigrada st. saussurei Forel 1885:361. Worker: Mexico. Combination in Atta (Trachymyrmex): Forel, 1893:601; in Trachymyrmex: Gallardo, 1916:242. Raised to species: Forel, 1893:601.
Trachymyrmex smithi Buren 1944:5. Worker: Mexico. Current subspecies: nominal plus neomexicanus.
Atta (Trachymyrmex) squamulifera Emery 1896:100. Worker: Costa Rica. Combination in Trachymyrmex: Gallardo, 1916:242.
Trachymyrmex urichi subsp. panamensis Wheeler, W.M. 1925:38. Worker: Panama. Junior synonym of urichii: Weber, 1958:53.
Myrmicocrypta cucumis Mann 1922:45. (w.q.) HONDURAS. Combination in Trachymyrmex: Weber, 1958b:50. Junior synonym of bugnioni: Weber, 1967:273.
Trachymyrmex annulatus Santschi 1936b:201, figs. 6-9. (w.) PANAMA. Junior synonym of cornetzi: Weber, 1958b:49.
Trachymyrmex cornetzi subsp. gatun Weber 1940a:420. (w.q.) PANAMA. Junior synonym of cornetzi: Weber, 1958b:49.
Trachymyrmex morgani Weber 1940a:421. (w.) PANAMA. Junior synonym of bugnioni: Weber, 1967:273.
Trachymyrmex uncifer Santschi 1931c:281, figs. 16, 17. (w.) PANAMA. Junior synonym of cornetzi: Weber, 1958b:49.
Mayh-Nunes, A. J., and C. R. F. Brandao. 2002. Revisionary studies on the attine ant genus Trachymyrmex forel. Part 1: Definition of the genus and the Opulentus group (Hymenoptera : Formicidae). Sociobiology 40:667-698.
Mayh-Nunes, A. J., and C. R. F. Brandao. 2005. Revisionary studies on the attine ant genus Trachymyrmex Forel. Part 2: The iheringi group (Hymenoptera : Formicidae). Sociobiology 45:271-305.
Mayh-Nunes, A.J., and C. R. F. Brando. 2007. Revisionary studies on the attine ant genus Trachymyrmex Forel. Part 3: The jamaicensis group (Hymenoptera: Formicidae). Zootaxa 1444:1-21.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.firstname.lastname@example.org
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