Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Line drawing of face.
Range
Brown and Kempf's polytypic concept of iheringi: Guatemala south to northern South America (Venezuela, Colombia, Trinidad); Jamaica; southern Brazil (RS, SP, GO, RJ).
My narrower concept for Costa Rica (lowland dryforest of Guanacaste, lowland wet forest of Carara and Manuel Antonio, Atlantic lowland rainforest).
Identification
Face longitudinally rugulose, with 8 erect spatulate setae; mesosomal and gastral dorsa lacking erect setae; one or two stiff setae projecting from posterior face of hind coxa, a long, fine, flexuous seta projecting laterally from near spiracle on peduncle of petiole, fine seta projecting anteroventrally from anterolateral border of postpetiole (figure; Brown and Kempf discovered these setae and proposed a sensory function; I have not seen them on any other Octostruma species); color red; HW 0.73 (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.
This species appears to favor open, lowland habitats. It follows a pattern in which "amphitropical" species (those with range disjunctions, abundant in Central America and southern South America, but absent or uncommon in Amazonia) favor open or dry-forest habitats. I have collected the species in Winkler samples from Santa Rosa National Park, Finca La Pacifica, Carara Biological Reserve, and Manuel Antonio National Park. At La Selva Biological Station it appears rare, but has been collected in Project ALAS Berlese samples from one second growth forest site, and I collected an alate queen in the lab clearing.
Type data
Rhopalothrix iheringi Emery 1888:361. Holotype alate queen: Brazil, Rio Grande do Sul State [MCSN].
Rhopalothrix simoni Emery 1890:67. Syntype worker: Venezuela, Caracas [MCSN]. Synonymized by Brown and Kempf 1960.
Rhopalothrix godmani Forel 1899:41, pl. 3, fig. 4. Holotype alate queen: Panama, Chiriqui Province, David [BMNH]. Synonymized by Brown and Kempf 1960.
Rhopalothrix simoni var. wighti Wheeler 1908:161. Syntype worker: Jamaica, 2mi W. Port Antonio, Road to Shotover, 500ft altitude [AMNH, MCZC]. Synonymized by Brown and Kempf 1960.
Rhopalothrix (Octostruma) simoni race spei Forel 1912:196. Syntype worker: Colombia, foot of Sierra Nevada de Santa Marta, Hacienda de la Esperanza [MHNG]. Synonymized by Brown and Kempf 1960.
Rhopalothrix (Octostruma) simoni spei var. sulcata Santschi 1936:201. Syntype worker: Panama, Pueblo Viejo [NHMB]. Unavailable quadrinomial. Identified as iheringi by Brown and Kempf 1960.
Taxonomic notes
Brown and Kempf had a very broad concept of iheringi, and included an extensive discussion of variation in their revision. They synonymized a number of forms under iheringi, but greater resolution of this complex will require reevaluation of these synonymies.
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. 1888 ("1887"). Formiche della provincia di Rio Grande do Sul nel Brasile, raccolte dal dott. Hermann von Ihering. Bull. Soc. Entomol. Ital. 19:352-366.
Emery, C. 1890. Voyage de M. E. Simon au Venezuela (Decembre 1887 - Avril 1888). Formicides. Ann. Soc. Entomol. Fr. (6)10:55-76.
Forel, A. 1899. Formicidae. [part]. Biol. Cent.-Am. Hym. 3:25-56.
Forel, A. 1912. Formicides neotropiques. Part II. 3me sous-famille Myrmicinae Lep. (Attini, Dacetii, Cryptocerini). Mem. Soc. Entomol. Belg. 19:179-209.
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.
Santschi, F. 1936. Contribution a l'etude des fourmis de l'Amerique du Sud. Rev. Entomol. (Rio J.) 6:196-218.
Wheeler, W. M. 1908. The ants of Jamaica. Bull. Am. Mus. Nat. Hist. 24:159-163.
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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