Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Minor worker: head length 0.59mm, head width 0.53mm, scape length 0.58mm, Webers length 0.72mm (n=1). Head rounded behind; promesonotum evenly arched, mesonotal suture very weak; propodeal spines small but distinct; face and pronotum smooth and shining, katepisternum and lateral propodeum feebly foveolate; postpetiole grossly swollen; dorsal pilosity abundant, long, flexuous, some setae on mesosomal dorsum branched near apex, branches minute; color brown.
Major worker: head length 1.22mm, head width 1.21mm, scape length 0.65mm (n=1). Face between frontal carinae with parallel longitudinal carinae, space between eyes and frontal carinae punctatorugose overlain with parallel longitudinal carinae, rest of face smooth and shiny; hypostomal margin nearly flat, with pair of very small, low tubercles, located about one third distance from midline to recessed teeth flanking mandibles (superficially looks like there are no hypostomal teeth); dorsal pilosity abundant; sparse subdecumbent setae projecting from sides of head in face view.
A cosmopolitan tramp found in many tropical and subtropical regions, introduced in New World tropics.
This species is an invasive pest ant in many parts of the world. Hoffman et al. (1999) documented an invasion of a rainforest patch in northern Australia. Although P. megacephala is usually associated with disturbed or depauperate sites, in this case it was able to invade a diverse tropical rainforest. In plots where P. megacephala was most abundant, native ants were almost completely extirpated. Abundance of other native invertebrates was reduced 42-85 percent in plots where P. megacephala occurred.
P. megacephala is reported from Costa Rica in Kempf (1972), but we do not know the source of this report. Longino has worked in Costa Rica nearly every year since 1979, but did not collect P. megacephala from Costa Rica until 1996, when it was found infesting the Hotel Galilea. He had commonly used this hotel during the previous decade, so the P. megacephala were clearly a new arrival. Since then, he has noticed the species in various sidewalk borders and planters in San Jose, and in the Hotel Cacts on the opposite side of San Jose from the Hotel Galilea. Thus, the species appears well established in the San Jose core. Its distribution elsewhere in the country is unknown. Cover identified one collection of the species from La Selva Biological Station (collected by L. Tennant, March 1989, carton nest, underside of Dieffenbachia leaf), but no other collections have been made at La Selva, in spite of extensive inventory work at the site (Project ALAS).
Pheidole megacephala is an exotic species with a potentially devasting impact on native invertebrate faunas, and its distribution and abundance should be closely monitored in Costa Rica.
Hoffman, B. D., A. N. Andersen, G. J. E. Hill 1999. Impact of an introduced ant on native rain forest invertebrates: Pheidole megacephala in monsoonal Australia. Oecologia 120:595-604.
Kempf, W. W. 1972. Catalogo abreviado das formigas da regiao Neotropical. Stud. Entomol. 15:3-344.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. email@example.com
Stefan Cover, Museum of Comparative Zoology, Harvard University, Cambridge MA 02138 USA. firstname.lastname@example.org
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