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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).
Morphologically, Discothyrea is a very distinctive genus of tiny, generally eyeless ponerines (Brown 1958a). The fourth abdominal segment is vaulted and directed anteriorly (a condition shared with Proceratium and some Gnamptogenys). The antenna has a club formed from a single, large terminal segment. The antennae are closely approximated. In all Costa Rican species there is a flat lamella projecting vertically between the antennae.
I have examined about 80 different collections of the genus, mainly from Winkler samples from different parts of Costa Rica. I find Discothyrea to be one of those cases in which there is evidence of multiple sympatric species in local communities, but the characters that separate species locally are not very stable geographically. The characters discussed below may vary continuously when examining specimens from many sites, but form discrete clusters when examining specimens from one site.
In my search for species boundaries, I have relied on the following characters:
Number of antennal segments. Number of antennal segments has been used as a species-level character in keys by Weber (1939) and Borgmeier (1949). But counting antennal segments on small Discothyrea is very difficult, and its use as a species-level character has been questioned (Brown 1958a). The scape, basal funicular segment, and terminal club are large and easily seen. The remaining funicular segments are small, ring-like, and may show partial fusion. In spite of the difficulties in counting, I have still found the number of these small segments a useful character. In some workers there are three or four distinct segments. In others there are more than four, but it is often difficult to determine if there are five or six (figure). On some specimens it may even appear that there are five on one side and six on the other. I have found that within local communities the number of antennal segments (6, 7 or more than 7) is stable and distinguishes species.
Lateral view of interantennal clypeal lamella. This vertical lamella between the closely approximated antennal fossae is generally triangular in shape, but its appearance varies greatly due to differences in details of shape and angle. The degree of extension of the anterior margin of the clypeus affects the appearance of the interantennal clypeal lamella. In some cases the clypeus extends forward and the angle of the triangular lamella is obtuse, such that in lateral view the lamella appears rectangular. In other cases the anterior margin of the clypeus is shortened, and the angle of the triangular lamella is acute. The lamella forms a smaller triangular tooth between the antennal fossae and is less visible in lateral view (figure).
Anterior border of interantennal lamella. In workers where the interantennal lamella appears rectangular, the anterior margin of the rectangle may be flat, or it may have a projecting subtriangular tooth on the lower half (figure).
Dorsal view of anterior clypeal margin. The anterior clypeal margin may be truncate with flattened medial portion and rounded lateral portions, or subtriangular to broadly and evenly rounded (figure).
Size and color. These characters are relatively constant within sites, but continuously variable among sites.
Surface sculpture. The face may be densely micropunctate and mat, or smooth and somewhat shiny.
Borgmeier, T. 1949. Formigas novas ou pouco conhecidas do Costa Rica e da Argentina (Hymenoptera, Formicidae). Revta Bras. Biol. 9:201-210.
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.
Brown, W. L., Jr. 1979. A remarkable new species of Proceratium, with dietary and other notes on the genus (Hymenoptera: Formicidae). Psyche 86:337-346.
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.
Weber, N. A. 1939. New ants of rare genera and a new genus of Ponerine ants. Ann. Entomol. Soc. Am. 32:91-104.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.firstname.lastname@example.org
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