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The Dacetini is a tribe of ants that are all predators, most of them small, cryptic elements of tropical forest leaf litter and rotten wood (Bolton 1998 and included references). Most of them have highly modified mandibles relative to the standard triangular mandible common to most other ants. Many have mandibles that are elongate, linear, and with opposing tines at the tip (convergent with other lineages such as Odontomachus in the Ponerinae). Others have elongate mandibles like serrated scissors. Others have serrated mandibles that curve ventrally. Dacetines are difficult to locate by visual search, but litter sifting followed by extraction in Winkler bags or Berlese funnels often yields abundant material.
Bolton (1999) discovered a major dichotomy in dacetine mouthpart morphology, related to distinct methods of capturing prey. In one group, the mandibles did not open very widely, they were more widely separated where they articulated with the head, they tended to have a series of teeth or denticles along the length of the mandible, they generally did not have enlarged teeth at the apex, and the labrum had a pair of distinct lobes projecting from the anterior border. This suite of characters was associated with a mode of prey attack, termed static pressure mode, in which after the strike the mandibles remained clamped on the prey, and the sting was applied to subdue the prey. In another group, the mandibles opened very widely, they were close together where they articulated with the head, they tended to have long, cylindrical shafts with enlarged apical teeth that engaged when the mandibles closed, the shaft lacked a series of teeth or denticles, instead having 0-2 teeth or denticles near the apical teeth, and the labrum was T-shaped, with no anterior lobes. This suite of characters was associated with a mode of prey attack, termed kinetic mode, in which the strike alone was sufficiently brutal to incapacitate the prey, and no subsequent pressure was needed. The immobilized prey could be lifted and carried back to the nest.
Bolton proposed a phylogenetic hypothesis in which the static pressure mode was the primitive condition in the tribe, and the kinetic mode evolved independently several times. He redrew the generic boundaries in the tribe, in light of this new information regarding the mode of action of the mandibles.
The Costa Rican fauna contains three of Bolton's newly defined genera: Acanthognathus, Pyramica, and Strumigenys. Acanthognathus is a small lineage that has independently evolved kinetic mandibles. Pyramica retains the primitive static pressure mode of predation. It is a very diverse genus with many morphologically divergent species groups, but they all share the suite of characters described above. Strumigenys is another lineage that has evolved kinetic mandibles. It appears to be a very successful lineage, with a large number of species and often high species richness within communities, but it does not show nearly the range of mandible morphology exhibited by Pyramica.
The changes require a major reshuffling of species names in genera. Several changes have consequences for the nomenclature of the Costa Rican fauna. The genera Glamyromyrmex, Neostruma, Smithistruma, and Trichoscapa are now junior synonyms of Pyramica, and all of their constituent species are moved to Pyramica. The genus Quadristruma is a junior synonym of Strumigenys, and thus Q. emmae becomes Strumigenys emmae. Finally, several species that were in Strumigenys are moved to Pyramica: eggersi, gundlachi, subedentata, and trieces.
Finally, Bolton (2000) is a large, two-volume set, with over a thousand pages, that provides a global, species-level revision of the Dacetini (with some taxa for some faunal regions being provided by Brian Fisher and Steve Shattuck). There are separate keys to Neotropical Pyramica and Strumigenys, and there are individual species accounts containing complete synonymy, morphological descriptions, and range data. Five new species of Costa Rican Pyramica were described by Longino (2006).
In 2001 I made a short video of a live colony of P. paniaguae. Click here to view the video.
Literature Cited
Bolton, B. 1998. Monophyly of the dacetonine tribe-group and its component tribes (Hymenoptera: Formicidae). Bulletin of the Natural History Museum London (Entomology) 67:65-78.
Bolton, B. 1999. Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae). J. Nat. Hist. 33:1639-1689.
Bolton, B. 2000. The ant tribe Dacetini, with a revision of the Strumigenys species of the Malagasy Region by Brian L. Fisher, and a revision of the Austral epopostrumiform genera by Steven O. Shattuck. Memoirs of the American Entomological Institute 65:1-1028.
Longino, J. T. 2006. New species and nomenclatural changes for the Costa Rican ant fauna (Hymenoptera: Formicidae). Myrmecologische Nachrichten 8:131-143.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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