Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica to Colombia (Brown 1958, Lattke 1995). Costa Rica: scattered records from wet forests of both slopes, to 1200m.
Identification
Propodeum armed with a pair of long, slender spines, normally at least as long as the distance between the inner sides of their bases.
Notes
This species occurs in the Penas Blancas Valley to 800m, at La Selva and in Braulio Carrillo to 500m, near Turrialba, on the Osa Peninsula from sea level to 700m, and at Las Cruces at 1200m. Brown (1958) also reports collections from the old collecting sites Zent, Hamburg Farm, and Colombiana farm (in the Atlantic lowlands near Limon). One of these collections contained a male, which Brown briefly described. G. C. Wheeler collected a colony in the Bocas del Toro region of Panama, and he and J. Wheeler described and figured the larva (1952).
Workers from the Osa Peninsula have a smaller subpetiolar process, with posterior angle or tooth weak or absent. In contrast, the posterior tooth is strongly developed on Atlantic slope workers.
Natural History
This species is apparently a specialized millipede predator. While working in Corcovado National Park in the early 1980's, I observed some spectacular group raiding behavior. My first two encounters were groups of ants attacking large millipedes in the trail. My third encounter was at the initiation of a raid, and I spent longer observing it. A column of 20 workers was moving along a liana on the forest floor. They left the liana and moved very slowly across the leaf litter, frequently bunching up. They all went under a leaf, and then agitated ants could be seen coming out from under the leaf, 2 or 3 ants at any one time, cleaning their antennae and mandibles. I removed the leaf and discovered the ants attacking a large millipede. Some were stinging it and some were pulling on its legs. At that point I collected the millipede and some workers. The distance from where I first sited the phalanx to where they were attacking the prey was 6m. In an attempt to locate the nest I followed a returning worker as far as I could into a treefall tangle, 10m from the prey, before I lost site of it. On a subsequent day I observed a second raid by the same colony. At 1100hrs I saw 46 ants move down a branch and enter a hole in a rotten log. After 10min I broke open the log and exposed the ants attacking a very large millipede. The millipede was 6cm long, the same species as before. Very slowly and apparently with great difficulty, the ants were able to pull the millipede up onto the branch, and then they began to carry it back toward the nest. It appeared that almost every leg of the millipede had a worker clinging to it, and the millipede was being stretched by the ants pulling in opposite directions. I ended my observations at that point.
The millipedes I collected with G. bispinosa were identified by R. L. Hoffman as Trichomorpha sp. (Polydesmida: Chelodesmidae) and Epinannolene sp. (Spirostreptida: Epinannolenidae) (material sent to Lattke, who had them identified; see Lattke 1995).
Although I have seen scattered workers in Atlantic slope forests, I have never seen them attacking millipedes there. However, in the Penas Blancas Valley I once observed some workers crossing a trail and moving around a rotten log. As I broke open the log near where the ants were moving, I found pieces of millipede exoskeleton inside.
Type data
Ectatomma (Holcoponera?) bispinosum Emery 1890:40. Holotype (unique syntype) worker: Costa Rica, Jimenez (Alfaro).
Literature Cited
Brown, W. L., Jr. 1958. Contributions toward a reclassification of the Formicidae. II. Tribe Ectatommini (Hymenoptera). Bulletin of the Museum of Comparative Zoology 118:175-362.
Emery, C. 1890. Studi sulle formiche della fauna neotropica. Bolletino della Societa Entomologica Italiana 22:38-80, pls. 5-9.
Lattke, J. E. 1995. Revision of the ant genus Gnamptogenys in the New World (Hymenoptera: Formicidae). Journal of Hymenoptera Research 4:137-193.
Wheeler, G. C., J. Wheeler 1952. The ant larvae of the subfamily Ponerinae, Part I. American Midland Naturalist 48:111-144, 5 pls.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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