Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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SEM images of worker: whole worker lateral view (reduced, original); head, face view (reduced, original); head, lateral view (reduced, original); antenna (reduced, original); clypeus (reduced, original).
Range
Costa Rica (type locality), Colombia, Mexico (Chiapas and Veracruz). In Costa Rica this is the most common species. It occurs in wet to moist forests throughout the country, from near sea level to cloud forests at 1700m. It is more abundant in montane and cloud forest than in lowland rainforest.
Identification
Antennae 8-9 segmented; interantennal lamella subrectangular in lateral view; in face view anterior margin of clypeus shallowly convex to flat; interantennal lamella usually lacking an anterior tooth in side view; color red brown to nearly black (antennal club contrastingly yellow on dark specimens).
In the Atlantic lowlands there are discrete differences between testacea and horni. In testacea 1) the anterior margin of the clypeus is subtriangular in face view, 2) in lateral view the clypeus usually has a pronounced anteroventral tooth, and 3) the body color is orange yellow. In horni 1) the anterior margin of the clypeus is flattened, 2) in lateral view the clypeus usually lacks an anteroventral tooth, and 3) the body color is red brown. However, some material from other sites is intermediate with respect to these characters:
1. Some specimens from near Monteverde and Cerro Cacao (INBIOCRI001280523, INBIOCRI001279724, INBIOCRI001279723, INBIOCRI001279710) have the anterior margin of the clypeus somewhat projecting, intermediate between lowland testacea and horni. The coloration matches horni, and I tentatively identify them as horni.
2. A specimen from Manuel Antonio (INBIOCRI001279719) has the anterior clypeal margin flattened like horni, but has the orange yellow body color of testacea. I tentatively identify this specimen as testacea. Other Pacific lowlands specimens of testacea (Carara: INBIOCRI001279728, La Pacifica: INBIOCRI001279726) are more typical.
Natural History
Discothyrea are extremely small, cryptobiotic inhabitatants of forest leaf litter (Brown 1958a). Workers and queens of the genus occur frequently in sifted leaf litter samples, but are never numerically abundant within samples. They are difficult to collect any other way. They are specialized predators on arthropod eggs, particularly spider eggs (Brown 1958b, 1979, Levieux 1977, Dejean and Dejean 1998).
In Costa Rica, workers and queens of horni are relatively common in berlese samples of soil/litter, and in Winkler samples of sifted leaf litter.
Notes
Weber's isthmica is possibly a junior synonym of horni. Weber (1940) described isthmica from a single dealate queen from Barro Colorado Island, Panama. He stated "[isthmica] is separated from horni by the distinctly tuberculate epinotum and in having the node not sharply angulate above." In the description he stated that the anterior margin of the head was "produced as a convex lobe, slightly emarginate medially." These characters do not serve to differentiate isthmica from Costa Rican specimens I identify as horni. Queens of horni from Costa Rica have (1) rounded propodeal tubercles, (2) the anterior margin of the clypeus emarginate or broadly rounded, and (3) the sharpness of the petiolar node variable. Weber also stated that isthmica was differentiated from testacea by testacea's much larger size. I do not know on what evidence he based the statement, but workers I identify as testacea are not larger than horni.
Type data
Discothyrea horni Menozzi 1927:270. Holotype queen: Costa Rica, San Jose (Schmidt) [DEIC] (examined).
Literature Cited
Brown, W. L., Jr. 1958a. Contributions toward a reclassification of the Formicidae. II. Tribe Ectatommini (Hymenoptera). Bull. Mus. Comp. Zool. 118:175-362.
Brown, W. L., Jr. 1958b(1957). Predation of arthropod eggs by the ant genera Proceratium and Discothyrea. Psyche 64:115.
Dejean, A., and A. Dejean 1998. How a ponerinae ant acquired the most evolved mode of colony foundation. Insectes Sociaux 45:343-346.
Levieux, J. 1977. La nutrition des fourmis tropicales. V. Elements de synthese: les modes d'exploitation de la biocenose. Insectes Sociaux 24:235-260.
Menozzi, C. 1927. Formiche raccolte dal Sig. H. Schmidt nei dintorni di San Jose di Costa Rica. Entomol. Mitt. 16:266-277.
Weber, N. A. 1940. Rare Ponerine genera in Panama and British Guiana (Hym.: Formicidae). Psyche 47:75-84.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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