Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica, widespread in South America.
Identification
Median pronotal spines usually absent, occasionally present as low tubercles, never distinct spines; head not tapering behind eyes; head width less than or equal to 3.2mm; propodeal spines smoothly or irregularly conical, not carinate; dorsal face of propodeum with pair of indistinct blunt setose tubercles anterior to spines; workers of all sizes red to yellow-brown; head width less than or equal to 2.7mm.
Natural History
At La Selva Biological Station Acromyrmex octospinosus nests near ground level in mature forest. Nests have been observed in the bases of dead trees and under a piece of broken cement culvert in the leaf litter.
On 17 March 1993, mid dry season, I observed many alates, mainly queens, at La Selva Biological Station. They were at the lab clearing blacklight at 6:00am, suggesting a predawn nuptial flight.
Wetterer (1991) reports quantitative data on the foraging ecology of the species at La Selva.
Fernandez-Marin et al. (2003) report on nest founding behavior:
(Abstract) Foundresses of the leaf-cutting ant Acromyrmex octospinosus in central Panama forage for leaves as garden substrate (semi-claustral foundation). The fungal pellet and substrate usually are attached to rootlets, which are used as a platform for the garden. This arrangement keeps the garden suspended away from the earthen chamber of the underground nest during early colony growth, and we hypothesize that it serves to minimize contact between the garden and contaminants. A. octospinosus foundresses produce from 3 to 7 workers in 2.7 months after founding the nest, but workers do not forage for substrate at this time. Incipient nests died or were abandoned at a monthly rate of ca. 50%. We show that ants routinely clean their legs before manipulating the garden substrate. We also describe how foundresses use their fore-legs to rub the surface of the metapleural gland, and they then use typical grooming behaviors to pass the forelegs through the mouthparts, after which the ant then licks the garden substrate. Similarly, ants apparently use their mouths to transfer fecal droplets to their legs. We briefly discuss the functional significance of these grooming behaviors, and hypothesize that they are prophylactic behaviors that may help the foundress maintain a hygienic garden.
Taxonomic notes
Formica octospinosa Reich 1793:132. Syntype worker: French Guiana, Cayenne.
Given the presence of cryptic species in the octospinosus complex (Schultz et al. 1998), there is no compelling evidence that what I am calling "octospinosus" in Costa Rica is really conspecific with octospinosus in French Guiana (the type locality). In Costa Rica, I use the name "octospinosus" as shorthand for "some other member of the octospinosus complex probably distinct from echinatior."
Literature Cited
Fernandez-Marin, H., J. K. Zimmermann, and W. T. Wcislo. 2003. Nest-founding in Acromyrmex octospinosus (Hymenoptera, Formicidae, Attini): demography and putative prophylactic behaviors. Insectes Sociaux 50:304-308.
Schultz, T. R., D. Bekkevold, and J. J. Boomsma. 1998. Acromyrmex insinuator new species: an incipient social parasite of fungus-growing ants. Insectes Sociaux 45:457-471.
Wetterer, J. K. 1991. Foraging ecology of the leaf-cutting ant Acromyrmex octospinosus in a Costa Rican rain forest. Psyche 98:361-371.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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