TAR Terrestrial Arthropod Reviews 5 (2012) 3–14 brill.nl/tar Geographic spread of Pyramica hexamera (Hymenoptera: Formicidae: Dacetini) in the southeastern USA Joe A. MacGown1,* and James K. Wetterer2 1Department of Entomology and Plant Pathology, Mississippi State University, Mississippi State, Mississippi 39762 USA 2Wilkes Honors College, Florida Atlantic University, 5353 Parkside Drive, Jupiter, Florida 33458 USA *Corresponding author; e-mail: [email protected] Received: 11 October 2011; accepted 27 October 2011 Summary Pyramica hexamera is a tiny predatory ant that feeds on minute soil arthropods. Originally from East Asia, P. hexamera has been recently introduced to North America, apparently through human commerce. Here we document the known range of P. hexamera in Asia and the New World. We compiled and mapped 73 site records of P. hexamera, all from East Asia and the southeastern US. In Asia, P. hexamera records range from 21.9°N to 36.4°N (earliest date and number of sites in parentheses) in Japan (1949; 25), South Korea (1982; 2), and Taiwan (1992; 6). In the US, P. hexamera records range from 28.6°N to 34.3°N: in Florida (1987; 2), Louisiana (1987; 5), Mississippi (2003; 32), and Alabama (2007; 1). Pyramica hexam- era is reported for the first time from Alabama. © Koninklijke Brill NV, Leiden, 2012 Keywords Dacetine ants; biogeography; biological invasion; exotic species; invasive species Introduction Dacetines (Hymenoptera: Formicidae: Dacetini) are predatory ants that generally feed on tiny soil arthropods (Wilson, 1953). Members of this group are small, cryptically colored, and slow moving. They rarely forage openly above ground and become motionless when disturbed. As a result, most people, including field biologists, remain unaware of their presence even in areas where they are common. For example, Carroll (2009) surveyed 15 bayhead tree-islands in the Florida Everglades and did not find any dacetines in visual searches, yet found dacetines in Berlese extractions of leaf litter from 14 of the 15 islands. © Koninklijke Brill NV, Leiden, 2012 DOI 10.1163/187498311X615754 4 J.A. MacGown and J.K. Wetterer / Terrestrial Arthropod Reviews 5 (2012) 3–14 Over 900 species and subspecies of dacetine ants are currently recognized (Bolton et al. 2007). Of the 37 dacetines reported from the southeastern US, four are Old World exotics (Deyrup and Cover, 2009; MacGown and Hill, 2010). Three of these have already achieved broad distributions in both the Old World and the New World, spread through human commerce: Strumigenys emmae (Emery), Strumigenys rogeri Emery, and Pyramica membranifera (Emery) (Wetterer, 2011). In the US, only P. mem- branifera is naturalized across the southern states; S. emmae and S. rogeri are naturalized only in peninsular Florida (Wetterer, 2011). In this paper we document that the fourth species, Pyramica hexamera (Brown), is spreading across the southeastern US. The first reported collection ofP. hexamera outside its native Asia was in 1987 from Marion County, Florida (Deyrup, 1988). This species was again collected in Florida in 1998 in Hernando County (Deyrup, 2003), but has not been reported from the state since that time. Pyramica hexamera was also collected in West Feliciana Parish, Louisiana in 1987 (Bolton, 2000). Subsequently, it was collected from another site in West Feliciana Parish in 1999, in St. Tammany Parish in 2000, East Baton Rouge Parish in 2003, and Iberia Parish in 2003 (Dash, 2004). The first reported collections from Mississippi were from Chickasaw (2003, 3 sites), Lauderdale (2003, 1 site), and Jones Counties (2004, 2 sites) (MacGown et al., 2005). To examine the geographic spread of P. hexamera, we compiled and mapped speci- men records from its native and exotic range. Taxonomy and identification Brown (1958) described Epitritus hexamerus (= P. hexamera) from two sites in Japan. Bolton (1999) transferred E. hexamerus to Pyramica. Baroni Urbani and De Andrade (2007) synonymized Pyramica with Strumigenys. More recently, Bolton and Alpert (2011) reconfirmed Pyramica as a valid genus. Pyramica hexamera is a minute (~2.0 mm in total length), brown ant with elongate mandibles, each of which terminates with a long apicodorsal tooth (Figure 1A,B). Pyramica hexamera has spongiform tissue present ventral to the petiole and postpetiole (Figure 2A), and large, scale-like setae present on much of the dorsal surface of the body except the gaster (Figures 1A,B and 2A-D). Pyramica hexamera is unlikely to be confused with any other related dacetine in the southeastern US (Deyrup and Cover, 2009). Biology Pyramica hexamera is a specialized ambush predator of small long-bodied soil arthro- pods, such as Diplura, Chilopoda, and Collembola (Masuko, 1984). Masuko (2009) reported, “Diplura composed 60% of the prey in the field material.” This prey prefer- ence is unusual compared with most dacetines whose biologies have been studied, and which apparently prey primarily on Collembola (Masuko, 2009). Foraging P. hexamera workers hunt for their prey in small crevices in the soil. Upon encountering prey, P. hexamera moves to a crouching position, pulls its antennae back into recessed J.A. MacGown and J.K. Wetterer / Terrestrial Arthropod Reviews 5 (2012) 3–14 5 Figure 1. Pyramica hexamera worker: (A) profile view, and (B) full-face view. antennal scrobes lining the side of the head, closes its mandibles, and remains motion- less. The ant may remain still for >20 min while it waits for the prey to advance and crawl on top of its head. Pyramica hexamera is uniquely equipped for this situation, having a flattened head and slightly upturned mandibles (Figure 1A), each of which 6 J.A. MacGown and J.K. Wetterer / Terrestrial Arthropod Reviews 5 (2012) 3–14 Figure 2. Pyramica hexamera worker: (A) spongiform tissue beneath petiole and postpeti- ole, (B) full-face view showing scales covering head, scapes, and mandibles, (C) close-up view of mandibles showing scales and elongate apicodorsal teeth, and (D) close-up of scales on head. terminates with a sharp apical tooth (Figure 2B,C), allowing the ant to strike at prey passing overhead. Additionally, the entire dorsal surface of the head is covered with large scale-like setae, which may be sensory in nature (Figure 2B,D). When the prey is in the correct position, the ant opens its mandibles and suddenly snaps them shut, impaling the prey with the apical teeth (Masuko, 1984). Pyramica hexamera has also been reported to coat its body with soil and other detritus using its forelegs, a behavior that may camouflage the ant’s odor from the prey (Masuko, 1984). Methods Using published and unpublished records; we documented the worldwide range of P. hexamera. We obtained unpublished site records from museum specimens in the J.A. MacGown and J.K. Wetterer / Terrestrial Arthropod Reviews 5 (2012) 3–14 7 collections of Archbold Biological Station (ABS, identified by M. Deyrup), the Mississippi Entomological Museum (MEM, identified by J. MacGown), the Museum of Comparative Zoology (MCZ, identified by S. Cover), and the Smithsonian Institution (SI, identified by B. Bolton). In addition, we used on-line databases with collection information on specimens by the Essig Museum of Entomology at the University of California, Berkeley (UCB), Antweb (www.antweb.org), and the Global Biodiversity Information Facility (www.gbif.org). We obtained geo-coordinates for collection sites from published references, speci- men labels, maps, or geography web sites (e.g., earth.google.com, www.tageo.com, and www.fallingrain.com). If a site record listed a geographic region rather than a “point locale,” and we had no other record for this region, we used the coordinates of the larg- est town within the region or, in the case of small islands and natural areas, the center of the region. We did not map records of P. hexamera found in newly imported goods or intercepted in transit by quarantine inspectors. Published records usually included collection dates. In a number of cases, publications did not include the col- lection dates for specimens, but we were able to determine the approximate date based on information on the collector’s travel dates or limit the date by the collector’s date of death. Results We compiled and mapped P. hexamera specimen records from a total of 73 sites (Table 1; Figure 3). In Asia, P. hexamera records range from 21.9°N to 36.4°N in Japan, South Korea, and Taiwan. In the US, P. hexamera records range from 28.6°N to 34.3°N: in Florida, Louisiana, Mississippi, and Alabama (Figure 4). Figure 3. Map showing the worldwide distribution of Pyramica hexamera. 8 J.A. MacGown and J.K. Wetterer / Terrestrial Arthropod Reviews 5 (2012) 3–14 Table 1. Earliest known records for Pyramica hexamera from East Asia and the United States. # of sites Earliest record Japan 25 1949 (Brown 1958) Taiwan 6 1982 (Terayama and Kubota 1989) South Korea 2 <1992 (Kim et al. 1992) Florida 2 1987 (Deyrup 1988) Louisiana 5 1987 (Bolton 2000) Mississippi 32 2003 (MacGown et al. 2005) +Alabama 1 2007 (J. Lasiter, MEM) + = no previously published records. MEM = Mississippi Entomological Museum. Most records we found of P. hexamera from Asia, where this species of ant is native, are from Japan (25 sites) (Bolton, 2000; Brown, 1958; Masuko, 2009; Ogata and Onoyama, 2003; Sato et al., 2010; Shimazaki and Miyashita, 2005; Terayama and Kihara, 1998; Yamauchi and Ogata, 1995). Only six records have been reported from Taiwan (Anonymous, 1999; Terayama et al., 1995; Terayama and Kubota, 1989) and only two from South Korea (Kim et al., 1992; Lyu et al., 2001; Park and Kim 2002). We compiled 40 site records of P. hexamera from the US, all from the Southeast. By far, the majority of records of this species from the southeastern US have been from Mississippi (32 site records).