Pheidole bilimeki is a member of the Neotropical P. punctatissima clade, together with P. anastasii and P. punctatissima (Economo et al. 2015). Among species treated here, it is easily confused with the aforementioned and members of the P. flavens complex. Minor workers can also be confused with those of P. parva. See section under P. anastasii for identification notes. In the southeastern United States, P. bilimeki is often confused with P. floridana Emery, which is discussed in more detail below. In the Neotropics, there are many native species that closely resemble P. bilimeki (Wilson 2003).
We propose the synonymy of P. lauta Wheeler to be transferred from P. floridana to P. bilimeki. In his original description Wheeler (1908c) wrote, “…the worker has the base of the gaster opaque whereas this is shining in the specimen of floridana given me by Prof. Emery.” The description and the photographs we have examined of the type specimens all agree with the concept of P. bilimeki used here and in Longino and Cox (2009).
Should P. floridana therefore be synonymized under P. bilimeki? Wilson (2003) offered that the former might represent the northernmost population of the latter, and recent phylogenetic analyses (Economo et al. 2015; Moreau 2008) show these two as sibling taxa. Based on the results of her analysis, Moreau (2008) found that her samples of P. bilimeki (Costa Rica, RA0162) and putative P. floridana (Florida, RA0331) were each other’s closest relatives, and that this pair was sister to P. anastasii (Costa Rica). The result is also supported by Economo et al. (2015), which found a shallow divergence separating P. bilimeki from putative P. floridana, especially compared to the deep divergence separating these sister taxa from P. anastasii. Moreau (2008) concluded that in order for P. anastasii to be a valid member of P. bilimeki, as proposed by Wilson (2003), P. floridana would also have to be accepted as a synonym of P. bilimeki.
We suggest that this conundrum stems from the common misapplication of the name P. floridana (a shiny gaster species) to collections of what are in fact the North American population of P. bilimeki (a matte gaster species). Naves (1985) came to a similar conclusion in his revision of the Pheidole of Florida, “P. floridana seems to be confined to southeast Florida in the Miami area. This is the only place where I was able to locate this species. Due to its close relationship to P. anastasii the latter has been misidentified as P. floridana many times, thus, mistakenly extending the supposed range of P. floridana. P. anastasii is actually the species widely distributed in Florida, while floridana is absent or at least must be rare in most of the state.”
One explanation for the confusing phylogenetic results is that RA0331 actually refers to P. bilimeki Mayr, and that true members of P. floridana Emery from the Miami area were not included in the aforementioned phylogenetic analyses. The samples of RA0331 were collected in central Florida from Polk County, well outside the Miami area from which the P. floridana Emery is known (Naves 1985). Deyrup, who collected and identified the specimens of RA0331, has previously (2003; 1988; 1989) applied the name P. floridana to matte gaster specimens that earlier authors (Naves 1985; Smith 1933; Wheeler 1932) would have considered P. anastasii Emery, and that we consider P. bilimeki Mayr.
To properly ascertain the taxonomic status of P. floridana Mayr we suggest a future phylogenetic analysis that includes specimens matching the type material of P. floridana, preferably from the Miami area. If there is evidence supporting the conspecificity of samples matching our concept of P. bilimeki, then the validity of P. floridana Emery must be revaluated. If, rather, the P. floridana samples are heterospecific with respect to P. bilimeki, then there are at least two hypotheses that could explain this result. One is that P. floridana is endemic to Florida. The second, perhaps more compelling albeit ironic explanation, would propose the Miami population of P. floridana is conspecific with a Neotropical species inadvertently introduced to Florida. Miami is a major shipping port and was the gateway for many introduced ants over the past two centuries (Deyrup et al. 2000).
The taxonomic confusion surrounding whether published accounts refer to our proposed concept of P. bilimeki, or instead to either P. floridana or P. anastasii, makes it difficult to ascertain the natural history of the species. The following account given by Longino and Cox (2009), however, refers definitively to P. bilimeki. They report that P. bilimeki is a common species in open, recently or frequently disturbed habitats. In Costa Rica it occurs in lowland dry forest, lowland wet forest, and montane habitats to about 1500 m elevation. It is a common ant of roadsides, nesting under stones or in dead fence posts. It is a frequent pest ant in houses and is a common ant at baits in second growth dry forest vegetation in seasonally dry Guanacaste Province. It can also be abundant and dominant in large disturbances deep within primary forest reserves. We tentatively treat the account given by Wilson (2003) for P. floridana as referring to the North American population of P. bilimeki. That account stated that winged reproductives have been found in nests during September and October, and that the species occurs in a variety of woodland habitats, nests in soil, litter, and rotten wood, and in both xeric and mesic situations. It also noted the observation of Stefan Cover that colonies are monogynous, may contain 1000 or more ants, and are sometimes polydomous. Cover observed that the species is omnivorous, but does not appear to harvest seeds (but see Naves 1985). Naves (1985) discussed the biology of P. bilimeki (as P. anastasii) in Florida. He found the species most often nesting under the bark at the base of pines or along the roots, but occasionally found it nesting in the soil. The colonies he observed supported over 600 workers with a 5:1 ratio of minors to majors. Mature colonies were monogynous, although in laboratory conditions colonies that lost their original queen would accept other conspecific queens. Several colonies were discovered with two or three founding females, but laboratory experiments found that one would kill the others before the rearing of the first brood. Naves also recorded that the species feeds on seeds, fruits, and scavenges on small dead arthropods and is predaceous on small live arthropods.
Pheidole bilimeki is a synanthropic species with a high tolerance for habitat disturbance. It is occasionally found indoors, especially in greenhouses. There is little indication that is causes significant impact to agricultural systems or native ecosystems.
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 broad and flat. Color usually brown, occasionally brownish yellow to yellow. Scape index (SI) = 95–108. Major worker characters. Antennal scapes do not extend beyond posterior margin of head. Posterolateral lobes distinctly punctate and lacking rugae. Head reddish brown or more rarely yellowish, 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 red brown, rarely yellow brown. Major | HW 0.75–1.04, HL 0.79–1.13, SL 0.44–0.57, CI 87–97, SI 50–65 (n=39, Longino pers. comm.). Head uniform in color; subquadrate; often entirely punctate, but portions of posterolateral lobes can be glossy. Posterolateral lobes never with distinct rugulae. Promesonotum in profile forming a single dome. Postpetiole relatively broad; distinctly more than 2x petiolar width in dorsal view. First gastral tergite with anterior third to entire surface matte. Minor | HW 0.42–0.52, HL 0.47–0.59, SL 0.40–0.54, CI 83–93, SI 88–108 (n=38, Longino pers. comm.). Head, including the area mesad of the frontal carinae, entirely covered by reticulated network of punctures, giving it a dull appearance. Posterior head margin relatively broad and flat. Antennal scapes lack standing hairs; 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 is a Neotropical native that ranges from northern South America to southern North America and across the Caribbean. The records included here from the southern United States have previously been treated as P. anastasii and P. floridana (see discussion). Pheidole bilimeki was not reported from Florida until 1932 (Wheeler). While it is possible that the penetration of P. bilimeki into the southern United States represents a recent dispersal event, even one that has been anthropogenically facilitated, there are several reasons for considering P. bilimeki as native to the region. Firstly, the range of North American populations appear contiguous with those of Mexico and the Caribbean, and gene flow among them is probable. Secondly, populations from Florida are known to host two parasites, a mermithid that parasitizes workers, and a hymenopteran parasite species of the genus Orasema (Naves 1985). Pheidole bilimeki has been recorded from greenhouses in Illinois and Ohio in North America. The species has also been found indoors and greenhouses across Europe, including the Netherlands (Boer and Vierbergen 2008), Germany (Forel 1908), Great Britain (Forel 1908), Ireland (Stelfox 1927), and Switzerland (Forel 1908). The only occurrence of P. bilimeki in Jamaica is reported by Wilson (2003). Although the species might occur there, it is also possible that Wilson was referring to P. jamaicensis Wheeler. The single Mauritius occurrence is of a single minor worker examined by Donisthorpe (1946), but this specimen more likely refers to the superficially similar P. parva which is widespread across the island and its neighbors in the Indian Ocean.