Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica (Monteverde, Hitoy Cerere Biological Reserve).
Identification
Face crossed by a sharp, clearly defined arcuate carina; anterior portion of face concave, differentiated from posterior portion, delimited by frontal carinae and facial arc; face and vertex lobes shiny; mesosoma short, compact; dorsal and posterior face of propodeum meeting to form broad, shallow, obtuse angles, not forming distinct acute propodeal teeth; mesosoma and gaster devoid of erect setae; HW 0.53 (n=1).
Natural History
The genus Octostruma is known only from the New World tropics, from southern Mexico and the West Indies to northern Argentina (Brown and Kempf 1960). It is a part of the "cryptobiotic" fauna: small, slow-moving ants that live in rotten wood and leaf litter. The very similar genus Eurhopalothrix is known to be predaceous on small, soft-bodied arthropods (Brown and Kempf 1960, Wilson 1956, Wilson and Brown 1985).
Workers and nests are extremely difficult to see in the field. Some species camouflage themselves with layers of soil (Hoelldobler and Wilson 1986). As a result of their cryptic nature, they were considered extremely rare until the 1960's. But increasing use of Winkler and Berlese sampling has shown Octostruma to be relatively common. I encounter them in most Winkler samples from wet forest sites in Costa Rica.
I know this species from 4 Winkler samples from the Monteverde cloud forest (all from ridge-top cloud forest, not from moist forest lower in community), and one Winkler sample from 200m elevation rainforest in Hitoy Cerere Biological Reserve.
Taxonomic notes
This species is very similar to rugiferoides Brown and Kempf. It matches the size data given by Brown and Kempf, and the head shape exactly matches their figure. Their figure of the face shows a pair of spatulate setae near the midline of the vertex margin, and 8 setae distributed evenly along the arcuate carina. None of the material from Costa Rica has setae on the vertex margin. The number on the facial carina is variable, from 2 to 10. When there are few, they are situated laterally, near the eyes. rugiferoides is described with vertex lobes and mesosoma granulose-punctate and opaque, whereas JTL-010 has shiny vertex lobes, and the anterior portion of the mesosoma is shiny. The propodeal teeth of rugiferoides were not explicitly described, but by implication from the described similarity to rugifera, rugiferoides may have more developed spiniform teeth than JTL-010.
rugiferoides is known from Mexico, and the nature of character change between Mexico and Costa Rica is unknown.
Octostruma rugiferoides Brown and Kempf 1960:200. Holotype worker: Mexico, Veracruz, near Tetzonapa, Pueblo Nuevo [MCZC].
Literature Cited
Brown, W. L., Jr., Kempf, W. W. 1960. A world revision of the ant tribe Basicerotini. Stud. Entomol. (n.s.) 3:161-250.
Hoelldobler, B., Wilson, E. O. 1986. Soil-binding pilosity and camouflage in ants of the tribes Basicerotini and Stegomyrmecini (Hymenoptera, Formicidae). Zoomorphology (Berl.) 106:12-20.
Wilson, E. O. 1956. Feeding behavior in the ant Rhopalothrix biroi Szabo. Psyche (Camb.) 63:21-23.
Wilson, E. O., Brown, W. L., Jr. 1985 ("1984"). Behavior of the cryptobiotic predaceous ant Eurhopalothrix heliscata, n. sp. (Hymenoptera: Formicidae: Basicerotini). Insectes Soc. 31:408-428.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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