The following account is from Sarnat et al. (2015).
Pheidole anastasii, P. bilimeki and P. punctatissima all belong to the P. punctatissima clade (Economo et al. 2015). These ants are all relatively small species characterized by densely punctate ground sculpture that gives them a dull, matte appearance. Among species treated here, the P. punctatissima clade species are most easily confused with those of the closely related P. flavens complex. Major and minor workers are most reliably diagnosed from those of the P. flavens complex by the relatively broad postpetiole and the matte anterior portion of the gaster in addition to other characters listed in the key. The minor workers can also be confused with those of Asian native P. parva, but can be distinguished by the more uniform and stout mesosomal hairs, and by the antennal scapes which lack erect hairs and tend to surpass the posterior head margin by a distance equal to or greater than eye. In the Neotropics, there are many native species that closely resemble P. anastasii (Wilson 2003), and identification of the minor worker subcaste is especially challenging.
Among introduced members of the clade, the major workers of P. punctatissima are immediately distinguished from those of both P. anastasii and P. bilimeki by the bicolored head. The minor workers of P. punctatissima tend to have narrower posterior head margins and longer antennal scapes than those of P. anastasii and P. bilimeki. Separating P. anastasii from P. bilimeki is particularly difficult. They are most reliably distinguished by ecological characteristics, with the former preferring to nest arboreally and the latter preferring to nest under stones or in dead wood. The morphological characters separating these two species are highly variable, but the major workers of P. anastasii tend more often towards yellow (versus tending towards brown in P. bilimeki) and can have relatively wider heads (HW 0.74–1.16 mm vs. 0.71–1.07 mm). The minor workers of P. anastasii tend to have more narrow heads posteriorly then P. bilimeki and relatively longer scapes (SI 103–125 vs. 95–108). See Longino and Cox (2009) for additional details.
Adding to the already confusing taxonomy separating P. anastasii and P. bilimeki is the widespread application of the name P. floridana Emery to populations across the southern United States. The first record of P. floridana from Florida was the type series described by Emery from Coconut Grove (Miami area) in 1895. Smith (1930) recorded P. floridana in his original list of Florida ants, and added P. anastasii three years later (1933), stating only “This species [P. anastasii], which was originally described from Costa Rica, is recorded here for Florida on the basis of information secured from Dr. Wheeler…I have seen the same species in greenhouses in the District of Columbia, New Jersey, and Illinois.” The previous year (1932) Wheeler, who had received type material of P. floridana from Emery (Wheeler 1908c), included P. floridana and P. anastasii in his own list of Florida ants.
Naves (1985) in his study of Florida Pheidole, also recognized both species and distinguished P. anastasii from P. floridana by the matte base of the gaster in the former and the glossy gaster in the latter. Indeed, the type specimens of P. floridana from Coconut Grove are consistent with this characterization (CASENT0904424, CASENT0904425). Naves wrote that the Miami area was the only place where he was able to locate P. floridana. Pheidole anastasii, in contrast, was reported by Naves as widely distributed across the state.
Deyrup et al. (1988), lamenting the taxonomic confusion surrounding P. floridana, P. flavens and P. anastasii in Florida, stated, “Traditionally (Creighton 1950; Smith 1979) the name P. floridana has been applied to a widespread upland species that has a distinctive matte area on the base of the first gastral tergite and very evenly rugose head…This is the species we report from the Keys [Florida].” Subsequent reviews of Florida ants have thus excluded P. anastasii from their lists (Deyrup 2003; Deyrup et al. 2000; Moreau et al. 2014). Wilson (2003) followed Deyrup in treating all outdoor populations from the United States as P. floridana, but conceded that his concept of P. floridana could represent a northern geographic variant of P. bilimeki or an endemic species modified by intergradation with a P. bilimeki immigrant population.
With respect to all outdoor North American records, we follow Wheeler (1932), Smith (1933), and Naves (1985) in treating the localized glossy-gaster P. floridana as distinct from the widespread matte-gaster species referred to as P. anastasii by the aforementioned authors. However, the relatively short scapes and posteriorly broad heads of the minor workers, together with the habitat and nesting preferences of the matte-gaster species suggests the name P. bilimeki Mayr more accurately applies to this widespread taxon than does P. anastasii Emery. The issue is discussed in further detail under the P. bilimeki section.
Pheidole anastasii, named by Emery on behalf of Sig. Anastasio Alfaro, is a Neotropical species that is occasionally found indoors beyond its native range. Although at least some arboreal colonies appear to be polydomous, P. anastasii is a low-impact adventive that has thus far shown little capacity for becoming a significant invader. The biology of P. anastasii, especially across its native range in Costa Rica and in comparison to P. bilimeki was reviewed by Longino and Cox (2009). The species was noted as being among the most abundant ants in the low arboreal forest understory of La Selva Biological Station (Costa Rica). Although tolerant of disturbance, P. anastasii requires some vegetation cover and does not occur in open areas. All collections reviewed by Longino and Cox were from wet forest habitats. Most were from below 500 m elevation, but several ranged to a maximum of 1200 m. The propensity for the species to be inadvertently transported to greenhouses across the world is predicted by its arboreal foraging and nesting habits. Longino and Cox (2009) observed the species nests in almost any kind of cavity or sheltered space, including live stems, and that workers often build galleries and tunnels with carton or earthen construction. The species was reported to occur in lowland second growth, evergreen forest, coffee plantation, limestone, ravine, mixed hardwood-pine forest, wet forest, on karst, and cloud forest. It was also reported to nest in dead sticks and branches on or above the forest floor, under bark flaps on tree trunks, beneath epiphytes and under stones.
P. anastasii is a synanthropic species with a high tolerance for habitat disturbance. It is occasionally found in human habitations and in greenhouses. There is little indication that is causes significant impact to agricultural systems or native ecosystems. The species is a quarantine risk, and is thought to be transported with fresh plant material.
Diagnosis of worker among Antkey species. Worker castes bimorphic. Head shape ovoid (minor workers) or subrectangular with posterolateral lobes (majors), but never triangular. Antenna 12-segmented. Antennal club 3-segmented. Antennal insertions at least partly covered by frontal lobes; not surrounded by a raised sharp-edged ridge. Frontal lobes do not obscure face outline between mandible and eye; relatively close together so that the posteromedian portion of the clypeus, where it projects between the frontal lobes, is at most only slightly broader than one of the lobes. Posterolateral corners of head unarmed, without spines. Mandibles triangular. Mesosoma with erect hairs. Pronotal spines absent. Propodeum armed with spines or teeth. Slope of mesosoma steep. Waist 2-segmented. Petiole pedunculate with a distinct and upright node; lacking large subpetiolar process. Postpetiole attached to lower surface of gaster; not swollen; in dorsal view not distinctly broader than long or distinctly wider than petiole. Minor worker characters. Antennal scapes extend beyond posterior margin of head. Antennal scrobe lacking. Postpetiole not swollen relative to petiole. Hairs on mesosoma stout and stiff, arranged in pairs. Head punctate; posterior head margin relatively narrow and rounded. Color yellow to brownish yellow. Scape index (SI) = 103–125. Major worker characters. Antennal scapes do not extend beyond posterior margin of head. Posterolateral lobes distinctly punctate and lacking rugae. Head yellowish or rarely reddish brown, but never bicolored with the yellowish posterior two-thirds contrasting with the darker brown anterior third and rest of body.
Diagnosis among introduced Pheidole. Color usually dull yellow to dull brownish yellow. Major | HW 0.83–1.05, HL 0.90–1.11, SL 0.49–0.62, CI 88–98, SI 50–61 (n=43, Longino pers. comm.). Head uniform in color; subquadrate; often entirely punctate, but portions of posterolateral lobes can be glossy. Posterolateral lobes never with distinct rugae. Promesonotum in profile forming a single dome. Postpetiole not swollen relative to petiole. Postpetiole relatively broad; distinctly more than 2x petiolar width in dorsal view. First gastral tergite with anterior third to entire surface matte. Minor | HW 0.38–0.50, HL 0.44–0.59, SL 0.44–0.58, CI 82–90, SI 106–120 (n=49, Longino pers. comm.). Head dull, entirely covered by reticulated network of punctures. Posterior head margin relatively narrow and rounded. Antennal scapes lack standing hairs; scapes surpass posterior head margin by a distance equal to or greater than eye. Promesonotum in profile forming a single dome, lacking a distinct mound or prominence on the posterior slope. Hairs on mesosoma stout, stiff, of equal length and arranged in pairs. Postpetiole narrow in dorsal view, only slightly broader than petiole. Gaster with at least anterior 1/3 of first tergite matte.
Diagnosis among introduced Pheidole. Color usually dull yellow to dull brownish yellow. Major | HW 0.83–1.05, HL 0.90–1.11, SL 0.49–0.62, CI 88–98, SI 50–61 (n=43, Longino pers. comm.). Head uniform in color; subquadrate; often entirely punctate, but portions of posterolateral lobes can be glossy. Posterolateral lobes never with distinct rugae. Promesonotum in profile forming a single dome. Postpetiole not swollen relative to petiole. Postpetiole relatively broad; distinctly more than 2x petiolar width in dorsal view. First gastral tergite with anterior third to entire surface matte. Minor | HW 0.38–0.50, HL 0.44–0.59, SL 0.44–0.58, CI 82–90, SI 106–120 (n=49, Longino pers. comm.). Head dull, entirely covered by reticulated network of punctures. Posterior head margin relatively narrow and rounded. Antennal scapes lack standing hairs; scapes surpass posterior head margin by a distance equal to or greater than eye. Promesonotum in profile forming a single dome, lacking a distinct mound or prominence on the posterior slope. Hairs on mesosoma stout, stiff, of equal length and arranged in pairs. Postpetiole narrow in dorsal view, only slightly broader than petiole. Gaster with at least anterior 1/3 of first tergite matte.Pheidole bilimeki, Pheidole punctatissima
Pheidole anastasii is a Neotropical native that ranges from Mexico to southern Central America or northern South America. We consider many of the outdoor records of P. anastasii from the southern United States to refer instead to P. bilimeki (see discussion above). There are, however confirmed records of the species from heated indoor locations—especially greenhouses. In North America there are records from hothouses in Washington D.C. and New York (Longino and Cox 2009), and also from Massachusetts. In Europe, the Netherlands occurrences reported as P. anastasii by Boer & Vierbergen (2008) refer to P. bilimeki (Boer, pers. comm.). The records from Denmark and Norway might also refer to P. bilimeki, but until specimens can be examined we follow the authors’ use of P. anastasii (Birkemoe and Aak 2008; Lomholdt 1986).