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Dacetine Ants in Southeastern North America (Hymenoptera: Formicidae)
Mark Deyrup and Stefan Cover

Southeastern Naturalist, Volume 8, Number 2 (2009): 191–212

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2009 SOUTHEASTERN NATURALIST 8(2):191–212 Dacetine Ants in Southeastern North America (Hymenoptera: Formicidae) Mark Deyrup1,* and Stefan Cover2 Abstract - Ants of the tribe Dacetini are especially diverse in Southeastern North America, with 40 known species, all in the genera Pyramica and Strumigenys. The 30 native Pyramica may represent a remnant Arctotertiary forest ant fauna. The 9 introduced species of Pyramica and Strumigenys come from both Old and New World tropics. Surveys of the southeastern fauna appear incomplete, and there may be additional undescribed species. All species are predatory, capturing small arthropods, especially Collembola, by means of a specialized jaw-snapping mechanism. The notable diversity in mandibular structure among species is unexplained in a functional sense. Arrays of specialized clypeal hairs, usually species-specific, may possibly lure prey. Specialized “spongiform bodies” in the petiolar area may be defensive. Local populations may be threatened by habitat loss, invasive exotic species, and climate change. Introduction Small, elusive, strikingly diverse, and remarkably ornate, the dacetine ants are the wood warblers of the myrmecological world. These ants lurk in leaf litter and rotten wood, where they stalk or ambush small soil organisms, especially springtails (Collembola; Brown and Wilson 1959). Southeastern North America is unusually well endowed with dacetine ants: 40 species are known from the region, and it is probable that there are additional species to be found. The purpose of this paper is to discuss the diversity, distribution, and origins of the group in the Southeast. In addition, we hope that this paper will encourage more southeastern naturalists to study these unusual ants, whose natural history remains poorly understood. In the Southeast, dacetine ants may be distinguished from other ants by their trap-like jaws and highly modified hairs, especially the hairs of the clypeus (e.g., Figs. 1–2). Most species have peculiar spongy cuticular growths on the “waist” area: the petiole, postpetiole, and first segment of the gaster (Figs. 1–3). For a more formal and precise definition of the tribe, applicable on a worldwide basis, see Bolton (2000). It once appeared that dacetine ants were relatively rare. Creighton’s (1950) manual of North American ants lists only 24 species, four of which were subsequently synonymized. At the time of the manual, many of these species were known from only one or two collections. This impression 1Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862. 2Department of Entomology, Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138. *Corresponding author - mdeyrup@archbold-station. org. 192 Southeastern Naturalist Vol. 8, No. 2 of rarity is an artifact of the small size and cryptic habits of the species. Dacetine ants probably occur in every woodlot in the southeastern and mid-Atlantic states, except for those at higher elevations of the Appalachians. It is not unusual to find several species in semi-disturbed woodland. I have often found species in urban or suburban habitats, for example, in Figure 1. Pyramica boltoni, known from Florida only. Several other southeastern species have whisker-like hairs with enlarged tips on the clypeus. Figure 2. Pyramica angulata, from Southeast and lower Midwest. The form of the mandibles and clypeus suggests that angulata clamps on to relatively large prey. 2009 M. Deyrup and S. Cover 193 backyards in Washington, DC. It is possible to train the eye to see these minute ants, which are typically slightly over 2 mm in length, as they slowly creep out of sight when exposed in a handful of leaf litter spread out on a tray. The abundance and diversity of dacetines, however, only became apparent when entomologists began to routinely use soil extraction devices. These devices, which are various modifications of the classic Berlese funnel, can be easily and cheaply produced (there is a diagram in Borror and DeLong 1971) or bought from biological supply houses. However, not all species of southeastern dacetines are common and widespread, or easily found by litter extraction. The taxonomy used here follows Bolton’s (2000) worldwide revision of the dacetines. Bolton’s revision, the first comprehensive treatment of the group, should serve as the foundation of future studies for many years. It features region-by-region keys for the identification of genera and species, descriptions of species, and scanning electron micrographs of most species. The sections on the Nearctic fauna include all but two of the known southeastern species. In addition to the printed version, this reference is also available on line at the Hymenoptera Name Serve site organized by N.F. Johnson ( home_page). Entering the name of a species described in Bolton (2000) (e.g., Pyramica metazytes) provides access to a browsable version of the entire reference. Keys to Nearctic Pyramica are on pp. 95–101, those for Strumigenys on pp. 496–507. Figure 3. Strumigenys lanuginosa, Neotropical, is a rare exotic in tropical Florida. The long hairs on the gaster are unusual for the genus; their function is unknown. 194 Southeastern Naturalist Vol. 8, No. 2 The information presented below is derived from literature sources, from the authors’ collecting and taxonomic work, and from the collections of Nearctic dacetines at the Harvard Museum of Comparative Zoology and at the Archbold Biological Station. A list of described southeastern dacetines appears in Appendix 1. Origins of Southeastern Dacetine Ants The southeastern dacetine fauna has dual origins. There is a group of 31 presumed native species, and a group of 9 presumed introduced species. Each of these groups presents points of interest. Native species The native species include 30 species of Pyramica and one species of Strumigenys, the widely distributed S. louisianae (Fig. 4). The latter species has a more or less continuous distribution across southern North America, through Central America, and into South America (Bolton 2000). It shares the Neotropics with several morphologically similar species that may be close relatives. In contrast, the native Nearctic Pyramica have a center of distribution in the southeastern Coastal Plain, Appalachian Piedmont, and the southern Mississippi Basin. Many of these Pyramica species are widely distributed, occurring from southern New York and New Jersey, south into northern Florida, west into the Ozarks and southeastern Kansas into the Figure 4. Strumigenys louisianae, found in southern North America through Neotropics. Many other dacetines, especially tropical species, have fl attened, silvery, spoon-shaped hairs. 2009 M. Deyrup and S. Cover 195 relatively mesic forests of eastern Texas. The fauna of southwestern North America north of Mexico is depauperate, with only four species, two of which are known from single collections (Ward 1988) from isolated mesic woodlands. Brown (1953) suggested that the southeastern fauna of Pyramica is most closely related to that of warm-temperate eastern Asia, rather than to the well-developed Neotropical fauna. This relationship is most obvious in Asian members of the rostrata complex that seem to share character states with the Nearctic P. rostrata: P. rostrataeformis (Brown) and P. incerta (Brown), both Japanese, and the Chinese P. emeswangi Bolton. Japanese species of the circothrix group, P. circothrix (Ogata and Onoyama) and P. hiroshimensis (Ogata and Onoyama), show similarities to the North American pergandei group (Bolton 2000) and have at least a superficial resemblance to some Nearctic members of the pulchella group, such as P. abdita. Photographs of the Japanese P. masukoi (Ogata and Onoyama) resemble some species in the Nearctic clypeata group. Images of these Japanese ants may currently be viewed on the Internet on the Japanese Ant Image Database organized by Hirotami Imae (Imae 2003). In short, native Pyramica in North America consists of an extensive, eastern fauna in the Appalachians and southern Mississippi Basin, a few apparently relict southwestern species, and evident affinities with the fauna of temperate eastern Asia. This distribution closely matches that of warmtemperate Arctotertiary flora discussed by Raven and Axelrod (1978). The southeastern Pyramica species represent the only extensive radiation of woodland ants in North America, and the only obvious assemblage of Arctotertiary ants. Future analysis may show that there are other groups of ants that fit this pattern, perhaps in the genus Proceratium and in species groups of Aphaenogaster and Camponotus. There is, however, no such group that begins to match the diversity of Pyramica. In Pyramica, we get a last glimpse of what must have been a fantastically rich ant fauna on the floor of the Arctotertiary forest. The remnant diversity we see today probably survived because these ants usually occur as small colonies of slow-moving individuals feeding on ubiquitous micro-arthropods in the shelter of moist leaf litter. These traits should have allowed populations of Pyramica species to survive in small refuges, such as ravines, valleys, and swamp forests, sites buffered from extremes, especially drought, during the repeated glacial episodes of the Pleistocene. These refuges were probably scattered throughout the southern Appalachians and the southern Mississippi Basin, where mixed mesic forests persisted in ravines and valleys (Delcourt and Delcourt 1984). The north–south orientation of both the Appalachians and the river valleys to the west would have allowed vegetation to move north and south with climatic fl uctuations, as opposed to the situation in Europe and parts of Asia, where east–west mountain ranges blocked such movements (Delcourt and Delcourt 1984). Southeastern Pyramica species with apparently restricted distributions seem to fall into 196 Southeastern Naturalist Vol. 8, No. 2 groups that are endemic to either the southeastern Appalachians and eastern Coastal Plain, or the more western forest corridors of the Mississippi and its tributaries. Eastern species include apalachicolensis, carolinensis, inopina, archboldi, boltoni, and deyrupi. Western species are filitalpa, bimarginata, rohweri, hyalina, and memorialis. This scenario, however, is still somewhat uncertain because some of these species are so rarely collected that their ranges are unclear. Introduced species Nine species of dacetines, including four species of Strumigenys and five Pyramica, have been introduced into the Southeast. Four species appear to have originated in the Old World. These are: Strumigenys emmae, S. rogeri, Pyramica hexamera, and P. membranifera (Deyrup et al. 2000). Five species are Neotropical: Strumigenys lanuginosa, S. silvestrii, Pyramica eggersi, P. gundlachi, and P. margaritae (Deyrup et al. 2000). All these introduced species appear to originate in tropical areas, with the exception of the Japanese species P. hexamera. In spite of these origins, only two species, P. gundlachi and S. lanuginosa, appear to be confined to tropical areas of Florida. Three species, S. rogeri, S. emmae, and P. eggersi, have ranges extending into northern Florida, where there are regular frosts and prolonged cold periods, although the ground does not freeze. The remaining “tropical” species, S. silvestrii, P. margaritae, and P. membranifera, have ranges extending slightly north of Florida, and west along the Gulf Coast. The nine exotic dacetines were probably introduced in nursery stock. Uninhibited movement of plants occurred from the early 1600s, while meaningful pest quarantine measures have been observed for less than a century. Many plants were transported in tubs of soil, such as the thousand breadfruit saplings that were to be transported on the ship Bounty from Tahiti to the West Indies. While these plants were tossed overboard after the famous mutiny, the undaunted Captain Bligh successfully imported even more tubs and pots of plants to the West Indies in 1792 (Popenoe 1920). In Florida, importation of tropical plants was encouraged by an 1838 Act of Congress. Before that, in the 1832 “Laws of Florida 10th Session,” The Florida Tropical Plant Company of the pioneering horticulturist Henry Perrine was incorporated, with the preamble: “Whereas the introduction in this Territory of useful tropical exotics is calculated to be beneficial to the citizens ...” Although many species were imported as seeds, grafted varieties of certain trees, such as citrus, mango, and avocado, were brought in as rooted stock. As an example of Perrine’s industry, he shipped more than a hundred boxes of rooted plants from the Yucatan to a lighthouse keeper on Key Biscayne (Douglas 1978). Many ants must have accompanied such shipments. While a tub of soil might suit many dacetines, there were other, more luxurious accommodations. The invention of “Wardian cases,” essentially small, portable greenhouses, might have furthered dacetine dispersal. These 2009 M. Deyrup and S. Cover 197 cases had ventilation holes with barriers to exclude sea spray, and the bottom of the case was filled with “light soil, leaf-mould, or a mixture of soil and sawdust” (Macmillan 1935), a perfect medium for dacetines. In transit, plants were given access to light and air, but kept in the shade; “plants in an active state should be given an occasional watering by an intelligent person” (Macmillan 1935). This advice could have come directly from a handbook for dacetine hobbyists, if such people had ever existed. Status of the Inventory of Southeastern Dacetines The list of species in Appendix 1 includes all known southeastern dacetines. There is an excellent chance that additional species, native or exotic or both, await discovery. Some species might already occur in collections. Bolton’s (2000) review of dacetines involved much of the material in major collections, and produced three undescribed southeastern Pyramica. Nonetheless, our studies of specimens of Florida dacetines revealed an additional species of Pyramica mixed in with a similar, described species (Deyrup 2006). It is probable that Bolton never saw this species, and it is possible that there are other local collections that include undescribed species. Whether or not there are unsuspected new species in collections, it is likely that there are additional species to be found in the field. One reason to suspect that there are additional species of native Pyramica is the fact that a number of species are known from only one or a few sites. This representation is an indication of an incomplete inventory in cases (as in the dacetines) where collection methods are inefficient, laborious, and undertaken by only a few researchers surveying a large area. Native Pyramica that have seldom been collected (Fig. 5) are P. apalachicolensis (three sites in Florida; Deyrup and Lubertazzi 2001), P. cloydi (type locality in Tennessee [Pfitzer 1951], two sites in Florida [Deyrup and Cover, unpubl. data]), P. inopina (three sites in Florida; Deyrup and Cover 1998), P. memorialis (type locality only, in Kentucky; Deyrup 1998) and P. rohweri (two sites in Mississippi; Bolton 2000). Species of ants that are only known from one or a few collections in a large study have been analyzed by Longino et al. (2002). One important category of rarely collected species is the “geographical edge species,” those that are common outside the survey area, but rarely stray into the survey area. Few, if any, native dacetines are likely to fit into this category because there are no species known to be confined to areas immediately north or west of southeastern North America. Another set of rare species in the survey by Longino et al. are “methodological edge species,” species that are only found dependably through special sampling methods that may or may not be known. Possible examples in the southeastern dacetine fauna are P. apalachicolensis, which was found in buried wood in wet pine fl atwoods without much litter (Deyrup and Lubertazzi 2001), and P. memorialis, which was found in small cavities in clay soil (Deyrup 1998), but our knowledge 198 Southeastern Naturalist Vol. 8, No. 2 of the nesting site of these species rests on one or two collections. It is also possible that there are some highly localized species whose restricted habitat has never been sampled by a myrmecologist. In summary, the Southeast is a gigantic and spectacularly varied territory when considered in the light of methods for sampling dacetines. There is no known way to attract or concentrate dacetines. Standing in a mesic southeastern woodland, surveying a huge array of microhabitats stretching out in all directions into the distance, one is struck by the enormity of the task of adequately sampling even a few hundred acres. Only through great good luck would one find a species whose colonies are as “rare” as Sciurus carolinensis Gmelin (Gray Squirrels) or nesting Baeolophus bicolor (L.) (Tufted Titmouse), or many other common vertebrates. There is no reason to doubt that there are species of dacetine ants whose colonies occur at low densities. Thus, the inventory of southeastern dacetines will remain incomplete until far more naturalists are involved in the effort. Figure 5. Heads of some apparently rare southeastern Pyramica; above, left to right: apalachicolensis (3 collections), cloydi (3 collections); below, left to right: inopina (3 collections), memorialis (1 collection). 2009 M. Deyrup and S. Cover 199 The inventory of non-native species is probably also incomplete. Not all introduced ants are abundant or widespread (Deyrup et al. 2000). Some introduced dacetines, such as P. eggersi, S. rogeri, and S. emmae, are so abundant as to occur predictably in certain habitats. Some other species, such as S. silvestrii, S. lanuginosa, P. hexamera, and P. margaritae, are seldom encountered. A rare exotic dacetine, especially one that has not moved far from its point of introduction, could be established for decades without ending up in a myrmecologist’s Berlese funnel. Unlike unreported native species, which might be in some relict pristine forest, unreported exotic species are most likely to be found in areas with a long history of extensive foreign commerce. In a sense, the inventory of exotic dacetines can never be complete so long as there are additional species that might be imported at any moment. The number of “geographic edge species” of potential exotic dacetines in the Southeast is theoretically huge, over 800 species, considering that the Southeast includes climatic regimes from tropical to warm temperate. In practice, only a tiny fraction of these species will ever arrive in the form of viable propagules, and many species may have biotic requirements that cannot be met in the Southeast, or, at least, in the vicinity of their port of entry. It would be possible, if there were sufficient interest, to extract ants from litter in disturbed sites in the tropics and warm-temperate Asia to generate a list of dacetines that are likely to be imported into the Southeast. We know of no database that would currently allow such predictions. There is an interesting list of the ants that were intercepted in USDA inspections between 1927 and 1985 (Suarez et al. 2005). Of 232 records, only 8 are dacetines, none of which are known to be established in North America north of Mexico. Dacetines, presumably, are under-represented in this list. However sharp-eyed the inspectors, they are unlikely to spot tiny, cryptic, slow-moving ants that can have an entire colony in a hollow twig the size of a match stick. Dacetines cannot be excluded by direct inspections, but rather by interdiction of untreated soil. This is routine today, but, as mentioned above, was neglected in the early days of commerce. The sheer volume of commerce and travel today may allow some untreated soil to slip past the inspection process. Plastic bags can serve as a simplified modern version of the extinct Wardian case. On one occasion, we collected 10 one-gallon bags of leaf litter in Georgia, carried them to Maine, returned to Florida a month later, and still extracted numerous Pyramica ohioensis and P. rostrata from this litter. From 4 one-gallon plastic bags of Florida leaf litter sealed for 38 days we extracted colonies (with queens) of the exotic Pyramica eggersi and Pheidole moerens Wheeler, as well as native Paratrechina faisonensis (Forel) and Eurhopalothrix fl oridana (Brown and Kempf). Today’s commercial plant importers are well aware of the potential hazards accompanying importation of untreated soil, but some private individuals may lack this caution and successfully smuggle into the Southeast desirable plants with associated soil 200 Southeastern Naturalist Vol. 8, No. 2 tucked into a plastic bag. We have conversed with a number of enthusiastic horticulturalists who have admitted, with little remorse, having smuggled growing plants from the tropics into the eastern US. The Southeast is not secured against additional exotic dacetines. Natural History Distribution, habitats, and microhabitats There are a few general patterns in species distribution. Some southeastern species occur throughout the Southeast and into the mid-Atlantic states, the lower Midwest, and eastern Texas. These species include S. louisianae, P. clypeata, P. dietrichi, P. laevinasis, P. missouriensis, P. ohioensis, P. ornata, P. pergandei, P. pulchella, P. refl exa, and P. wrayi. Several exotic species are confined to south and central peninsular Florida: S. lanuginosa, S. rogeri, S. emmae, and P. gundlachi. The region with the maximum number of species (32) is the lower Southeast, from north Florida to north Georgia and west to north Mississippi. Most southeastern dacetines occur in mesic wooded areas, but some are in open habitats, usually in grass tussocks or in pockets of accumulated leaf litter. Some species regularly inhabit disturbed and landscaped sites. The most extreme examples of this are P. eggersi and S. emmae, which may live in such unprepossessing habitats as the dusty mixture of pine mulch and cigarette butts beneath a row of small, scraggly viburnums bordering the parking lot of a south Florida shopping mall. There is surprisingly little evidence that any southeastern dacetines are limited to any particular ecosystem. There are, for example, no species known to be restricted to oak uplands, or pine forests, or hardwood swamp forests, or hardwood ravine forests. Species that are known from one or two sites could be restricted to the ecosystem types where they were found, but this needs to be confirmed by additional collecting. Even the microhabitat preferences of most southeastern dacetines are only known in a general way. Most species seem to require leaf litter that retains some moisture through the year. Thick litter that lacks dacetines may have been subjected to extreme drying at some point. This is often the case, for example, in the Florida Keys, where there is an extended dry season during the winter and spring. In many moist southeastern and mid-Atlantic sites, litter decomposition is so rapid during the summer that dacetines are restricted to rotten logs or pockets where litter accumulates. In such sites, litter tends to build up near conifers, whose needles are resistant to decomposition. Mixed hardwood and conifer litter often produces abundant dacetines. In our experience, there are relatively few dacetines in heavily shaded, cool sites, such as north-facing slopes of Appalachian ravines. The discouraging fact is that after decades of hunting dacetines, we remain unable to confi- dently identify sites that will yield a diversity of dacetines, or sites that might 2009 M. Deyrup and S. Cover 201 have one of the rarer species. The other side to this is that experts have little advantage over beginners, who are just as likely to make original contributions to the knowledge of dacetine natural history. Nests are usually in small, pre-formed cavities, such as beetle galleries in rotten logs. Where litter leaf is persistent and at least several centimeters deep, nests are often in hollow nuts, seedpods, old seed capsules of sweet gum, and small, hollow twigs. These nests are usually buried beneath the surface of the litter. In some situations, a patient myrmecologist can find these nests by sifting through litter and opening large numbers of hollow twigs or nuts. Colonies can also be found by dissecting rotten logs, bearing in mind that a whole colony may be in a small chunk of rotten wood. The most specific nesting site known for any North American dacetine is that of P. arizonica (Ward), which lives in fungus gardens of Trachymyrmex in arid areas of the Southwest, taking advantage of the constant humidity maintained by the leaf-cutter ants (Fisher and Cover 2007). No similar degree of specialization is known for any of the southeastern dacetines. Diet and predatory behavior Species of Pyramica and Strumigenys prey on soil microorganisms. Collembola (springtails) of the families Entomobryidae and Onychiuridae are the principle prey recorded in feeding trials (Brown and Wilson 1959; Dejean 1985; Matsuko 1984; Wilson 1950, 1953), but Symphyla, Diplura, and tiny centipedes are also collected, and may be the primary prey of P. hexamera (Matsuko 1984). Collembola of the families Poduridae and Sminthuridae are rejected in feeding trials, and may be defended by repellent chemicals (Wilson 1953). Collembola are often fantastically abundant, but are usually protected by an effective stored-energy escape mechanism: a tail-like appendage that is bent under the body and secured by a clasp on the ventral side of the abdomen. When a springtail needs to fl ee, it releases the tail, which strikes the substrate with enough energy to fl ing the springtail into the air. This speedy escape is countered by jaws of dacetines, which can snap shut in a fraction of a second, thanks to their own stored-energy mechanism (Bolton 1999, Gronenberg 1996, Wilson and Brown 1959). The jaws of Strumigenys and Pyramica have basal projections that lock on the lateral edges of the labrum. The jaws are cocked by opening them until their bases engage the labrum, then applying pressure with the massive muscles that close the jaws. These muscles take up two-thirds of the volume of the head (Gronenberg 1996), and account for the bulging posterior lobes of the head that are typical of dacetines (Figs. 1–12). A pair of trigger hairs project from between the open jaws. Some dacetines stalk their prey, while others seem to lurk in ambush. In either case, when the trigger hairs contact a prey, the labrum is retracted, releasing the jaws, which close with a convulsive snap on their victim. A simple diagram of this mechanism is provided by Brown and Wilson (1959), a more detailed treatment is in Gronenberg 202 Southeastern Naturalist Vol. 8, No. 2 (1996). The jaws of Strumigenys species are usually long and narrow (Figs. 3–4), so their apices achieve great velocity. They can strike with enough Figure 6. Pyramica hexamera, exotic from Japan, is widespread in the Southeast, apparently uncommon. This species ambushes its prey from underneath, and has well-developed dorsal apical teeth. Figure 7. Pyramica eggersi, exotic from Neotropics, is abundant in south and central Florida. The elongate mandibles seem convergent on those of typical Strumigenys, and the species was long placed in that genus. 2009 M. Deyrup and S. Cover 203 force to kill or disable prey instantly, and it is not always necessary to sting the prey after it is caught (Bolton 1999). The principle teeth are near the tips, where the strike force is greatest, usually impaling the prey (Bolton 1999). Predation by Pyramica species is less dramatic, but no less violent. The jaws are usually relatively short (Figs. 1, 5) and do not open as widely as in Strumigenys, but when they snap shut, their teeth grasp the prey firmly using a projection on the mandibular base that locks with the labrum and clypeus to prevent the jaws from being wrenched open by a struggling prey (Bolton 1999). The prey is then subdued by stinging (Bolton 1999). The jaws of southeastern dacetines are amazingly varied. Studies of the predatory behavior of several species (Brown and Wilson 1959; Dejean 1985; Matsuko 1984; Wilson 1950, 1953) show that Strumigenys with elongate jaws are more active hunters and more generalized in their diet than Pyramica that have short jaws and apparently specialize in the capture of Collembola. Matsuko (1984) provides considerable detail on the hunting behavior of several Oriental dacetines, including P. hexamera (Fig. 6), which has been introduced into the Southeast. This species crouches in Figure 8. Pyramica membranifera, exotic from Paleotropics, moderately common in the Southeast. The heavy, triangular mandibles and hairless body are unlike those of other southeastern dacetines. 204 Southeastern Naturalist Vol. 8, No. 2 narrow passageways in the soil, striking upward at centipedes and symphyla that step on its head. The jaws of P. hexamera are bowed, with enlarged, apical, spine-like teeth, and attached at an angle to the head, apparently well suited for an upward snap (Matsuko 1984). Other species of Pyramica that have been studied seem to feed primarily on Collembola (Brown and Figure 9. Pyramica missouriensis, known from New York into Florida, west into Missouri. The mandibles have a conspicuous toothless gap. Figure 10. Pyramica rostrata, known from Pennsylvania into Florida, west into Illinois and Texas. This species lacks a gap in the mandibular teeth. 2009 M. Deyrup and S. Cover 205 Figure 12. Pyramica inopina, known from three queens in Florida. This species lacks some normal dacetine features: spongiform bodies, enlarged mandibular teeth, enlarged lobes on the outer corners of the head, specialized hairs; these omissions suggest the species is possibly a social parasite of other dacetines. Figure 11. Pyramica archboldi, known from Florida and adjacent Georgia. This species has a triangular lamella on the mandibles. 206 Southeastern Naturalist Vol. 8, No. 2 Wilson 1959, Dejean 1985, Matsuko 1984, Wilson 1953). The diversity of mandibular form found in southeastern Pyramica, other than P. hexamera, is not understood in a functional sense, at least not in any detail. Some species, such as P. eggersi (Fig. 7) and P. gundlachi, have elongate jaws, others, such as P. membranifera (Fig. 8) have short, triangular jaws, and most have short and slender jaws (Figs. 1–2, 5, 9–12). Many species have a conspicuous gap between the basal and subapical series of teeth (Fig. 9), but some species lack such a gap (Fig. 10). In some species, the basal teeth are expanded into a triangular lamella (Fig. 11). In some species, the teeth of the subapical series alternate long and short. All these features, which are consistent within a species, might refl ect specialized prey preferences, or specialized methods of catching and holding similar types of Collembola. Different weapons may serve the same ends, just as the bow, the snare, and the sling all serve to hunt rabbits, with varying success, depending on the circumstances, and the specialized skill of the hunter with a particular weapon. Many species of Pyramica are notable for their highly modified hairs, especially on the clypeus. The form and arrangement of these is generally species-specific (Figs. 1–2, 5–6, 9–11). These may be related to predation, as suggested by their close proximity to the jaws. They might be tactile lures (Brown and Wilson 1959), and there is some evidence that they may be associated with chemicals that attract Collembola (Dejean 1985). These clypeal hairs are so elaborate, so precisely arranged, so consistent within a species, so diverse within the group, that it is difficult to doubt that they are the objects of some kind of selective evolutionary pressure. Taken together, the shape of the jaws, the size and arrangement of their teeth, and the apparently specialized hairs of the clypeus suggest an extravagant but mysterious evolutionary radiation. It may be some time before these morphological idiosyncrasies of the dacetines become understood. There is little prospect of following these minute predatory ants as they search for game along labyrinthine trails in the teeming sponge of last year’s leaves. With patience, however, it may be possible to accumulate enough behavioral information on captive colonies and records of prey remains found in nests to allow speculation on the meaning of morphological features of these ants. Defense It is probable that the jaws and sting of Pyramica and Strumigenys species, like those of other ants, can be used in defense as well as predation, although we have not observed this kind of active defense. When exposed or molested by a myrmecologist, dacetines usually become immobile, often for several minutes. They blend into their background of leaf litter or rotten wood, and are difficult to detect by the human eye. Southeastern dacetines are so tiny that it is unlikely that they are sought by any vertebrates, with the possible exception of small lizards, frogs, and salamanders. The primary enemies of dacetines are probably small spiders, centipedes, predatory 2009 M. Deyrup and S. Cover 207 beetles and their larvae, and ants. All these predatory arthropods swarm in the microhabitats of dacetines, as can be seen in any litter extraction. Most southeastern dacetines have spongy-appearing white structures, “spongiform bodies,” on the petiole, post-petiole and base of the gaster (Figs. 1–6, 8–11). From the position of these, they are probably defensive structures shielding the vulnerable joints between the mesosoma and the gaster. It is reasonable to suspect that these structures are also glandular, or associated with glands that produce defensive chemicals, but this has not been demonstrated. Somewhat similar structures, but thickly covered with white hairs, occur in the neck and petiolar regions of many Diapriidae, such as species of Monelata, Basalys, and other genera that we have often extracted from leaf litter. These small wasps are often parasitoids of fl ies that live in fallen fruit, fungi, manure, or ant nests (Masner and García 2002), microhabitats that attract many small predators, especially staphylinid beetles. Spongiform bodies have been lost in the rare, aberrant P. inopina (Fig. 12), and in the introduced species P. margaritae and P. eggersi (Fig. 7); they are vestigial in P. gundlachi. The exact function of the spongiform bodies is a major mystery of the dacetines. Threats to southeastern Dacetines There are no documented threats to southeastern dacetines, but it is unlikely that local populations are immune to the problems and crises that face many other organisms. Species that inhabit mesic woodlands, for example, are affected by widespread conversion of this habitat to intensive agriculture or forestry, to golf courses and so-called “gated communities” that are regularly drenched with insecticides, or paved over for cities and highways. If there are species that are highly restricted in their geographic range or have specialized habitats, these may be in particular danger, although it is not clear whether even the species that are rarest in collections are really rare in nature. Considering the problems of adequate sampling for dacetines, it is conceivable that the rarest species have never been found. It is possible that native dacetines in much of peninsular Florida are being displaced by introduced species, especially by S. rogeri, S. emmae, and P. eggersi. Some sites that produced native dacetines twenty or thirty years ago now produce exotic species, but there is no way to compare exact sampling sites or methods. Some sites in central Florida that “should” have native dacetines seem to primarily produce introduced species. The three most abundant exotics mentioned above seem to be expanding their ranges northward in Florida, so there may still be time for “before and after” methodical sampling. In parts of the Southeast, especially where the soil is mostly clay, introduced earthworms might be reducing or eliminating the thick litter layer where many dacetines live. Finally, many species of dacetines could become rare or locally extirpated if climate change in the Southeast takes the form of prolonged local droughts, perhaps accompanied by increased frequency of fires that remove leaf litter and rotten wood. 208 Southeastern Naturalist Vol. 8, No. 2 Further research The dacetine ants of the Southeast remain so poorly known that there are many opportunities for useful and original research. Sampling for dacetines is simple, and local surveys with Berlese funnels could fill in the ranges of many species, as well as improving knowledge on habitat and microhabitat preferences. As mentioned above, there is even the possibility of discovering undescribed species, which is more likely if surveys are done with some knowledge of local “hot spots” of endemism. Local naturalists might, therefore, be more successful in finding unusual dacetines than visiting expert entomologists. Even high school or undergraduate classes could become involved in sampling, exchanging, however momentarily, their enthrallment with the computer’s realistic fantasy for the fantastic reality of the leaf litter. Specimens can be identified by use of Bolton (2000), and most southeastern species have also been photographed for the Florida section of AntWeb, available on the Internet. The major impediment to these studies is access to a dissection microscope that provides good magnification. Studies of predation and defense are more difficult, but colonies can be kept in miniature, horizontal, plaster of Paris “ant farms,” with small, excavated chambers, and covered with a small glass plate, such as a microscope slide. Again, good magnification is necessary. Acknowledgments We thank Clifford Johnson, Lloyd Davis, and Walter Suter for their generous contributions of large numbers of specimens, significantly supplementing our own collections. We thank the managers of Florida State Parks for permitting collecting and for maintaining the natural habitats in which dacetines live. Two anonymous reviewers provided helpful suggestions. This work was supported by the Archbold Biological Station, Lake Placid, FL. Literature Cited Bolton, B. 1999. Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae). Journal of Natural History 33:1639–1689. Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute 65 (parts 1 and 2):1–1028. Borror, D.J., and D.M. Delong. 1971. An Introduction to the Study of Insects. Third Edition. Holt, Rinehart, Winston, New York, NY. 812 pp. Brown, W.L., Jr. 1953. Revisionary studies in the ant tribe Dacetini. American Midland Naturalist 50:1–137. Brown, W.L., Jr., and E.O. Wilson. 1959. 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Wilson, E.O. 1950. Notes on the food habits of Strumigenys louisianae Roger (Hymenoptera: Formicidae). Bulletin of the Brooklyn Entomological Society 45:85–86. Wilson, E.O. 1953. The ecology of some North American dacetine ants. Annals of the Entomological Society of America 46:479–495. 2009 M. Deyrup and S. Cover 211 Appendix I. List and known ranges of southeastern dacetine ants. Asterisk * denotes introduced species. Pyramica abdita (Wesson & Wesson) GA, IL, IA, IN, MD, OH, OK, TN, VA, IN, NC, PA (Bolton 2000), FL (Deyrup 2003) P. angulata (M. R. Smith) AL, KY, MS, OK, SC, AR, IL (Bolton 2000), GA (Ipser 2004), FL (Deyrup 2003) P. apalachicolensis Deyrup & Lubertazzi FL (Deyrup and Lubertazzi 2001) P. archboldi (Deyrup & Cover) FL (Deyrup and Cover 1998) P. bimarginata (Wesson & Wesson) IL, OH (Bolton 2000), MS (MacGown et al. 2005), MO P. boltoni Deyrup FL (Deyrup 2006) P. bunki (Brown) FL, GA, LA, MS (Bolton 2000) P. carolinensis (Brown) NC, SC, FL (Bolton 2000), GA (Ipser et al. 2004) P. cloydi (Pfitzer) TN (Bolton 2000), FL (Deyrup 2003) P. clypeata (Roger) AL, AR, FL, GA, KY, MD, OH, MS, NJ, NY, NC, PA, TN, TX, VA, IL, LA (Bolton 2000), OK P. creightoni (M.R. Smith) AL, DC, FL, GA, MS, NC, TN, VA (Bolton 2000) P. deyrupi Bolton FL (Bolton 2000) P. dietrichi (M.R. Smith) AL, AR, FL, GA, IL, KS, KY, LA, MD, MS, MO, NC, OH, OK, TN (Bolton 2000), TX P. eggersi (Emery)* Neotropics; FL (Bolton 2000) P. filirrhina (Brown) MO, NC (Bolton 2000) P. gundlachi Roger* Neotropics; FL P. hexamera (Brown)* Orient; FL, LA (Bolton 2000), MS (MacGown et al. 2005) P. hyalina Bolton IN, OH, MS (Bolton 2000), GA P. inopina (Deyrup & Cover) FL (Deyrup and Cover 1998) P. laevinasis (M.R. Smith) AL, AR, FL, GA, IL, KS, KY, MD, MS, NC, TN, TX, VA (Bolton 2000) P. margaritae (Forel)* Neotropics; AL, FL, GA, TX (Bolton 2000) P. membranifera (Emery)* Paleotropics; FL, LA, MS, TX (Bolton 2000), AL (MacGown and Forster 2005) P. memorialis (Deyrup) KY (Deyrup 1998) P. metazytes Bolton KY, TN (Bolton 2000), MS (MacGown et al. 2005), AL (MacGown and Forster 2005), FL P. missouriensis (M.R. Smith) IL, IA, KY, MO, MS, NC, NY, OH, VA (Bolton 2000), FL, SC P. ohioensis (Kennedy & Schramm) AL, AR, DE, FL, GA, IL, IN, KS, LA, MD, MO, NC, NJ, OH, TN, TX, VA (Bolton 2000), MS (MacGown et al. 2005), DC, OK P. ornata (Mayr) AL, AR, DE, DC, FL, GA, IL, IN, KY, LA, MD, MI, MS, MO, NC, OG, OK, SC, TN, TX, VA (Bolton 2000) P. pergandei (Emery) DC, IA, IL, IN, KS, MD, MA, MI, MO, NY, OH, PA, TN, VA (Bolton 2000), AL (MacGown and Forster 2005), GA (Ipser et al. 2004) P. pilinasis (Forel) AL, AR, DC, IL, IN, KY, KS, LA, MS, MO, NC, OH, PA, TN (Bolton 2000), GA (Ipser et al. 2004), FL (Deyrup 2003), OK, VA P. pulchella (Emery) AL, DC, DE, FL, IL, IA, IN, KS, KY, LA, MD, MI, MS, NC, NJ, NY, OH, PA, TN, VA (Bolton 2000), GA (Ipser et al. 2004) 212 Southeastern Naturalist Vol. 8, No. 2 P. refl exa (Wesson & Wesson) AL, AR, FL, IL, KS, NC, OH, TN, TX,WV (Bolton 2000), GA (Ipser et al. 2004), MS (MacGown et al. 2005) P. rohweri (M R. Smith) MS (Bolton 2000) P. rostrata (Emery) AL, AR, DC, GA, IL, IN, KY, LA, MD, MS, MO, NJ, OH, PA, TN, TX, VA (Bolton 2000), FL (Deyrup 2003), NC, SC P. talpa (Weber) NJ, DC, FL, GA, IL, LA, NC, OH, TN (Bolton 2000), MS (MacGown et al. 2005) P. wrayi (Brown) NJ, NC (Bolton 2000), GA (Ipser et al. 2004) Strumigenys emmae (Emery)* Pantropical, origin probably Australia; FL (Bolton 2000) S. lanuginosa Wheeler* Neotropics; FL (Bolton 2000) S. louisianae Wheeler Neotropics; AL, AR, FL, GA, LA, MS, NC, TN, TX (Bolton 2000), AZ S. rogeri Emery* Approaching Pantropical, origin probably Africa; FL (Bolton 2000) S. silvestrii Emery* Neotropics (Bolton 2000), FL (Deyrup 2003), AL