Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Images of queen: face view (small image, large image); lateral view (small image, large image).
Line drawing of balzani lectotype worker, from Brown and Kempf (1960).
Also see images of JTL-002, JTL-003, and JTL-011, by following links under Identification section.
Range
balzani complex: Tropical Mexico south through Central and South America at low and moderate elevations to the Bolivian Andes and to Parana and Sao Paulo states in southeastern Brazil; Trinidad, Dominica, and probably other islands of the Lesser Antilles (Brown and Kempf 1960).
JTL-001 (number of samples in parentheses): Santa Rosa (1), west of Monteverde at 900m (1), Carara (2), Manuel Antonio (1), 19km S Ciudad Neilly (1), Osa Peninsula (3), La Selva Biological Station (6).
JTL-002: Braulio Carrillo at 550m (1) and 800m (1), Penas Blancas Valley at 800m (5) and 1000m (2), Pitilla at 650m in Guanacaste Conservation Area (1), Monteverde at 1500m (1).
JTL-003: Hitoy Cerere (1), La Selva (4)
JTL-011: Hitoy Cerere (1), San Vito (1), Cerro Cacao (1).
Identification
balzani complex: vertex lobes uniformly punctate and opaque, never rugulose; face usually with 8 or more erect clavate setae, ground pilosity not evident; face rarely obscured by a layer of soil.
JTL-001: pair of setae on mesosomal dorsum; pair of setae on posterolateral margins of head; vertex arch barely discernable, face anterior to arch relatively more convex, weakly differentiated from face posterior to arch; color light red to dark red brown; HW 0.54-0.56 (n=2).
JTL-002: no setae on mesosomal dorsum; no pair of setae on posterolateral margins of head; vertex arch discernable, face anterior to arch somewhat flattened to concave, somewhat differentiated from face posterior to arch; color dark red brown; HW 0.62 (n=1).
JTL-003: a smaller, orange version of JTL-002; HW 0.53-0.55 (n=2).
JTL-011: setal pattern like JTL-001; differentiated face arch like JTL-002 and JTL-003; color dark red brown; HW 0.58-0.62 (n=3).
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 complex from numerous Winkler and Berlese samples from forested sites throughout Costa Rica, including rainforest, cloud forest, and dry forest.
Type data
Rhopalothrix balzani Emery 1894:217. Lectotype worker: Bolivia, Coroico [MCSN].
Rhopalothrix (Octostruma) lutzi Wheeler 1913:241. Lectotype worker: British West Indies, Dominica, near Roseau, Long Ditton [MCZC]. Synonymy by Brown and Kempf 1960.
Rhopalothrix (Octostruma) barberi Mann 1922:42. Holotype worker: Honduras, Alta Vera Paz, Trece Aguas [USNM]. Synonymy by Brown and Kempf 1960.
Rhopalothrix (Octostruma) equilatera Weber 1934:52. Syntype workers: Nicaragua, near San Miguel, Tuli Creek [MCZC]. Synonymy by Brown and Kempf 1960.
Taxonomic notes
Brown and Kempf (1960) treated balzani as a typical "polytypic" species, recognizing considerable variation within the species, and synonymizing a number of forms under it. I have tried to describe here the patterns of variation I see in Costa Rica. The four forms I recognize are very similar, and seem to exhibit different permutations of only a few characters, but there are spatial patterns in the characters, and what appear to be zones of sympatry.
As formulated here, JTL-001 is a common species throughout the Pacific lowlands, from Guanacaste dry forest to the rainforests of the Osa Peninsula, but also occurring at La Selva Biological Station. JTL-003 is perhaps widespread in the Atlantic lowlands. At La Selva, it seems quite distinct and clearly sympatric with JTL-001. JTL-002 is an upland, darker and larger version of JTL-003. It occurs on mid-elevation Atlantic slopes from the Cordillera Volcanica Central to the Cordillera de Guanacaste. The nature of the geographic transition from JTL-003 to JTL-002 is not clear, but they occur in close proximity near La Selva: JTL-003 is known from La Selva, and JTL-002 occurs as low as 550m on Volcan Barba just upslope a few kilometers from the south border of La Selva. JTL-011 is only known from 3 widely separated sites, and is an interesting mix of JTL-001 and JTL-002. It exhibits the setal pattern of JTL-001, but the size, color, and facial structure of JTL-002.
Brown and Kempf describe rugifera (Mayr), from southern Brazil, as being very similar to balzani except for the distinct arcuate carina on the face, a reduced number of erect setae on the face, and the mesosoma normally lacking erect setae. It is difficult to know how distinct is "distinct" for the facial carina, but JTL-002, JTL-003, and JTL-011 may be similar to rugifera.
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.
Emery, C. 1894. Studi sulle formiche della fauna neotropica. VI-XVI. Bull. Soc. Entomol. Ital. 26:137-241.
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.
Mann, W. M. 1922. Ants from Honduras and Guatemala. Proc. U. S. Natl. Mus. 61:1-54.
Weber, N. A. 1934. Notes on neotropical ants, including the descriptions of new forms. Rev. Entomol. (Rio J.) 4:22-59.
Wheeler, W. M. 1913. Ants collected in the West Indies. Bull. Am. Mus. Nat. Hist. 32:239-244.
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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