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Formicidae. Ants form a single family, the Formicidae, in the insect order Hymenoptera (ants, bees, and wasps). 83 genera of ants are known from Costa Rica. Technical keys to the ant genera of the world, complete with abundant illustrations, are available in works by Bolton (1994) and Hoelldobler and Wilson (1991). This guide relies both on the personal experience of the author and on the above two resources.
Habitus. Text notes with each genus often begin with an indication of whether the habitus is uniform or not. The habitus is the general appearance of the ant. Many genera are quite uniform in general appearance, with species differing only in minor characters of pilosity, surface sculpture, or allometric relationships. A genus with uniform habitus should be recognizable by the illustrations alone.
Characters. Important generic-level characters include: 1) mandible shape and dentition, 2) number of antennal segments, presence of antennal club, and number of segments in club, 3) presence of antennal scrobes (grooves on the face into which the antennal scapes can fold), 4) shape of the petiole, 5) degree of development and shape of postpetiole.
Subfamilies and selected tribes. Costa Rican ant genera are distributed in seven subfamilies, as listed below. The Myrmicinae contains several distinctive tribes, the genera of which are listed separately. Being able to place an ant in a subfamily or tribe will help narrow the search for particular genera.
Cerapachyinae: rare ants; subcylindrical with partially developed postpetiole; last abdominal segment with dorsal rows of peg-like teeth.
Dolichoderinae: common mostly arboreal ants; no postpetiole; anal orifice a transverse slit; usually with characteristic bleu cheese-like odor.
Azteca Bothriomyrmex Dolichoderus Dorymyrmex Forelius Linepithema Tapinoma Technomyrmex
Ecitoninae: army ants; with postpetiole; eyes reduced to single facet or absent; antennal insertions close together and exposed in face view; group raiding behavior.
Eciton Labidus Neivamyrmex Nomamyrmex
Formicinae: common mostly arboreal ants; no postpetiole; anal orifice a circular pore, often surrounded by an inverted cone of projecting setae; acid taste and odor.
Acropyga Brachymyrmex Camponotus (including subgenus Dendromyrmex) Myrmelachista Paratrechina
Myrmicinae: postpetiole present and always clearly distinct, much smaller than subsequent segment (abdominal segment 4).
Tribe Attini: the fungus growing ants; all with 11-segmented antennae.
Acromyrmex Apterostigma Atta Cyphomyrmex Mycocepurus Myrmicocrypta Sericomyrmex Trachymyrmex
Tribe Basicerotini: Basiceros is a large ant with 12-segmented antennae; other genera small ants with highly compact mesosoma, eight or fewer antennal segments.
Basiceros Eurhopalothrix Octostruma Rhopalothrix
Tribe Cephalotini: all arboreal ants with 11-segmented antennae, deep antennal scrobes.
Cephalotes Procryptocerus Zacryptocerus
Tribe Dacetini: small leaf-litter ants; mandibles variously elongate, with scissor-like blades or fork-like with terminal teeth; Acanthognathus with 12-segmented antennae, others with 6 or 4-segmented antennae.
Acanthognathus Pyramica Strumigenys
Other Myrmicinae, common or conspicuous genera
Aphaenogaster Cardiocondyla Crematogaster Leptothorax Megalomyrmex Monomorium Pheidole Solenopsis Tetramorium Wasmannia
Other Myrmicinae, rare or inconspicuous genera
Adelomyrmex Carebarella Hylomyrma Lachnomyrmex Oligomyrmex Rogeria Stegomyrmex Stenamma Tatuidris Tranopelta Xenomyrmex
Ponerinae: postpetiole absent or partially formed; sting present.
Common or conspicuous genera
Anochetus Ectatomma Gnamptogenys Hypoponera Leptogenys Odontomachus Pachycondyla Paraponera Platythyrea
Uncommon or inconspicuous genera
Acanthoponera Amblyopone Belonopelta Centromyrmex Cryptopone Discothyrea Heteroponera Prionopelta Probolomyrmex Proceratium Simopelta Thaumatomyrmex Typhlomyrmex
pseudomyrmecinae: common arboreal ants; postpetiole present; body subcylindrical; eyes very large.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. firstname.lastname@example.org