The tribe Dacetini is composed of small ants (usually under 3 mm long) that generally live in leaf litter where they prey on small arthropods, especially springtails (Collembola). The tribe has been formally defined by Bolton (1999, 2000). Nearctic dacetines may be recognized by a combination of features exemplified in Fig. 1 expanded, lobed occipital area of the head, elongate, narrowed projection of the head beyond the eyes, and the elongate, narrow mandibles. Most species have enlarged, spoon-shaped or otherwise modified hairs on the head, especially on the clypeus, and whitish, spongy processes on the petiole and post-petiole, as in Fig. 1. In spite of their striking appearance, and a diversity of character states that allow easy recognition of most species, the dacetines remain poorly known. This can be attributed to their small size and cryptic habits.

There are only two Nearctic genera of Dacetini: Strumigenys and Pyramica. Other genera listed for this region, for example, in Bolton's 1995 catalog of ants, were synonymized by Bolton (1999) in his reclassification of the genera of the Dacetini. In addition, certain species that had been assigned to Strumigenys were referred to Pyramica on the basis of a series of fundamental character states. In practice, Nearctic Pyramica may be recognized by their broad, well separated mandibular bases, while Strumigenys have narrow mandibular bases that appear to be attached near the midline of the head (Bolton 1999). Pyramica species use their mandibles to seize and hold prey until it can be stung, while Strumigenys species are able to snap their mandibles shut with such force that the prey may be killed outright (Bolton 1999). Bolton (1999) presents a detailed discussion of generic distinctions and the evolution of mandibular structure in the Dacetini.

Dacetine ants show their greatest diversity in moist tropical regions. The revision of the tribe by Bolton (2000) includes 872 species, only 43 of which occur in North America north of Mexico. Southeastern North America has the great majority of Nearctic species, including, by my count, 31 native species and 9 introduced species. The native species appear to represent a Nearctic radiation; only 1 native species has a range that extends into the Neotropics. It has been suggested (Deyrup 1988) that the diverse southeastern fauna is composed of species that persisted in mesic southeastern refuges during the climatic shifts of the Pleistocene, providing a partial glimpse of what was once a much richer Arctotertiary woodland fauna.

With this background, it is not surprising that additional species of dacetine ants are still being discovered in the Southeast. Not only are these ants small and cryptic, but some species may have relictual geographic distribution in isolated patches of habitat, or they may be dependent on a specialized microhabitat that remains unknown.

Pyramica boltoni Deyrup, new species

Discussion

Members of the genus Pyramica are usually most easily identified by characters of the head, especially the structures of the clypeus and mandibles and the modifications of the setae of the clypeus and antennal scapes. Pyramica boltoni shares clypeal character states with P. dietrichi, including the pointed clypeal shape with the tip turned up away from the plane of the mandibles, the decumbent apical setae, the set of radiating subapical setae, and the pair of elongate, curved setae arising near the apical third of the clypeus (Fig. 2). A third species, P. ornata (Mayr), shares these clypeal features, but the subapical setae are short and strongly expanded apically (Fig. 3). Pyramica boltoni is distinguished from P. dietrichi by having four, rather than six, radiating subapical setae, and by having the jaws protruding a shorter distance beyond the clypeus, so that the diastemma is barely visible in frontal view (Fig. 1 and Fig. 2). In addition, the sides of the pronotum of P. boltoni are primarily shiny, not reticulate as in P. dietrichi (Fig. 1 and Fig. 2). The pair of enlarged, upturned discal setae at the apical third of the clypeus are conspicuously larger than those of most P. dietrichi, but the size of these setae in P. dietrichi is somewhat variable, and it is possible that there might be overlap with those of P. boltoni in some populations. Pyramica boltoni keys to P. dietrichi in Bolton's (2000) key.

Several lines of evidence strongly suggest that P. boltoni is not a variant of P. dietrichi. The diagnostic features listed above are consistent in all the specimens examined from 38 separate collections spread over northern and central Florida. Pyramica boltoni is sympatric with P. dietrichi; there is no intergradation, and there are five known sites where both species occur. The diagnostic character states of the clypeal setae and the length of the mandibles relative to that of the clypeus are the kinds of character states that have been used in distinguishing many species of Pyramica, for example, in Bolton's key (2000). Unfortunately, these characters have not been associated with any natural history traits, but it is likely that such traits exist, given the consistency of the character states within each species of Pyramica.

Pyramica boltoni is known only from Florida, ranging from Highlands and Martin Cos. in the south-central Peninsula, north into St. John's Co. in the northeast corner of the state, and west into Jackson Co. in the central Panhandle. It might well occur in southern Georgia near the Florida border, but there are no known Georgia specimens. In Florida this species does not seem to be as widespread or abundant as P. dietrichi, which occurs throughout the state, including the Keys, north into Maryland and Illinois, and west into eastern Texas. I have examined 307 specimens of P. dietrichi from Florida, Georgia, Alabama, Arkansas, Oklahoma, Texas, and Illinois. Within the area where both species are known to occur, there is some evidence that P. dietrichi may occupy a wider range of habitats, specifically habitats that are wet, such as low flatwoods and swamp forest. Habitat information is available for 28 collections of P. boltoni and 49 collections of P. dietrichi; all specimens were extracted from leaf litter. Habitats of P. boltoni include xeric forest: 16 (57.1%); mesic forest: 11 (39.2%); wet forest, wet flatwoods: 1 (3.6%). Habitats of P. dietrichi include xeric forest: 23 (46.9%); mesic forest: 15 (30.6%); wet forest, wet flatwoods: 11 (22.4%). Pyramica dietrichi shows a significant difference in its greater preference for, or tolerance of, wet habitats (Chi square = 4.83, P value = 0.03).

Although the known distribution of P. boltoni is restricted relative to those of most native southeastern Pyramica species and it is not particularly common within this range, it cannot be considered a species that is rare or endangered. It is known from a series sites where its habitat might be expected to be protected including four state parks, one county park, two Nature Conservancy preserves, the Archbold Biological Station, the Ordway Preserve (managed by the University of Florida), and several sites in the Ocala National Forest.