Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Southern Mexico to northern Argentina. Costa Rica: widespread in Atlantic and Pacific slope wet forest, sea level to at least 1200m.
Identification
Black satiny surface; no erect setae on mesosomal dorsum; brown antenna tips. Nearly identical in morphology and behavior to P. apicalis, with which it is nearly always sympatric. Pachycondyla apicalis has bright yellow antenna tips, and the petiole is slightly more inflated with less distinct lateral margins posteriorly.
Natural History
In wet forested habitats of Costa Rica, this is one of the most common and conspicuous ants. Foraging workers are extremely fast and run over the surface of trails in a nervous, erratic manner, with the antennae rapidly vibrating. Their behavior is reminiscent of pompilid wasps. Foragers are solitary hunters on the ground, where they capture live prey. They are never arboreal. I have only seen diurnal foragers; I do not think they forage at night. I have not seen a nest.
Colonies typically have a reproductive queen, but workers exhibit dominance hierarchies among themselves, and may lay trophic or reproductive haploid eggs (Fresneau 1984, Oliveira and Hoelldobler 1991, Duessmann et al. 1996). Queenless colonies with reproductive intercastes may occur (Duessmann et al. 1996). Fighting amongst workers in establishing reproductive control has an energetic cost to the colony (Gobin et al. 2003).
Workers may exhibit tandem running, in which pairs of ants, one leading and one following, move toward a resource. Tandem running is mediated by a pheromone from the pygidial gland, which the lead ant rubs on its hind tibiae. The following ant maintains close contact with the lead ant, constantly antennating the hind legs of the lead ant (Hoelldobler and Traniello 1980, Traniello and Hoelldobler 1984).
In foraging, workers are able to use polarized light in orientation, and are able to judge distances (Duelli and Duelli-Klein 1976).
Workers may transport liquids between their mandibles, which they exchange with other workers (Hoelldobler 1985). Hoelldobler refers to this as an "external social bucket," which functions in the same capacity in social food exchange as the internal social crop of other ants. Carrying external liquid drops is considered a primitive condition relative to ants with a crop, and is exhibited by several other ponerines: Paraponera clavata, Ectatomma tuberculatum, Odontomachus sp., and Pachycondyla villosa.
I have twice observed obscuricornis workers with lepidopteran larvae as prey. Once I observed a worker with a skipper larva (Hesperiidae). The second observation, at La Selva Biological Station, was more detailed:
I watched a Pachycondyla obscuricornis worker attack and kill a lepidopteran larva. The larva was 1.7cm long and very fuzzy. The ant jumped on the back of the larva and the larva twitched violently, throwing the ant several cm away. This was repeated several times in rapid succession. Then the ant was able to hang on and kill the larva, because the larva suddenly went limp, and a pool of hemolymph appeared dorsally just behind the head. I saw both stinging and biting motions by the ant. The ant then tore at tufts of setae, and then began pulling the larva by the head.
Type Data
Pachycondyla flavicornis var. obscuricornis Emery 1890:58. Syntype worker: Brazil.
Literature Cited
Duelli, P., R. Duelli-Klein 1976. Freilandversuche zum Heimfindevermoegen suedamerikanischer Ameisen (Formicidae: Ponerinae, Dolichoderinae, Formicinae) [Field studies on homing ability in South American ants]. Studia Entomologica 19:409-420.
Duessmann, O., C. Peeters, B. Hoelldobler 1996. Morphology and reproductive behaviour of intercastes in the ponerine ant Pachycondyla obscuricornis. Insectes Sociaux 43:421-425.
Emery, C. 1890. Voyage de M. E. Simon au Venezuela (Decembre 1887 - Avril 1888). Formicides. Annales de la Societe Entomologique de France (6) 10:55-76.
Fresneau, D. 1984. Developement ovarien et status sociale chez une fourmi primitive Neoponera obscuricornis Emery (Hym. Formicidae, Ponerinae). Insectes Soc. 31:387-402.
Gobin, B., J. Heinze, M. StrŠtz, and F. Roces. 2003. The energetic cost of reproductive conflicts in the ant Pachycondyla obscuricornis. Journal of Insect Physiology 49:747-752.
Hoelldobler, B. 1985. Liquid food transmission and antennation signals in ponerine ants. Israel Journal of Entomology 19:89-100.
Hoelldobler, B., J. Traniello 1980. Tandem running pheromone in ponerine ants. Naturwissenshchaften 67:360.
Oliveira, P. S., B. Hoelldobler 1991. Agonistic interactions and reproductive dominance in Pachycondyla obscuricornis (Hymenoptera, Formicidae). Psyche 98:215-226.
Traniello, J. F. A., B. Hoelldobler 1984. Chemical communication during tandem running in Pachycondyla obscuricornis (Hymenoptera, Formicidae). Journal of Chemical Ecology 10:783-794.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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