The following account is from Sarnat et al. (2015) and figure numbers refer to that publication.
Pheidole flavens belongs to the P. flavens-complex along with a putatively large number of other nominal taxa, including P. moerens Wheeler. However, the P. flavens group as conceived by Wilson (2003) is now known to be polyphyletic (Economo et al. 2015; Moreau 2008). Readers are referred to the P. flavens-complex for additional discussion of this species identification, taxonomy and systematics. The taxonomy of P. flavens and its close relatives remains in a state of confusion. It is beyond the scope of the present study to resolve this issue, but we contribute the following discussion as a step towards that goal.
Pheidole flavens was originally described by Roger from Cuba, but the type material is considered to be lost. Wilson (2003) designated a neotype from Cuba and synonymized a total of eight nominal taxa with P. flavens. Of these, P. greggi Naves (Florida) and perhaps P. flavens st. spei Santschi (Mexico) are most similar to the Cuban neotype. They, together with the types of P. moerens subsp. creola, are the only specimens examined thus far that have clearly reticulated rugulae posterior to the scrobes of major workers. Naves (1985: fig. 55) concept of P. flavens Roger, at least as evidenced by his figures and descriptions, more closely matches our concept P. navigans, a species that is spreading across the southeastern United States. The syntype major of Pheidole flavens var. vincentensis Forel differs substantially from the neotype in that the head is completely glossy between the rugulae, which are themselves entirely longitudinal and do not extend far beyond the maximum extent of the antennal scapes in repose. These characters make it at least superficially more similar to P. moerens and P. navigans. Pheidole flavens r. gracilior and P. navigans were both described by Forel from workers intercepted at a Hamburg quarantine facility, which is testament to the dispersive ability of this complex. The syntype major of the latter species and that of P. floridana subsp. aechmeae Wheeler, also described from Mexico, are quite similar. Pheidole exigua var. tuberculata Mayr has the strongly convex head and promesonotal dome of P. exigua Mayr, and also exhibits tuberculate angles on the mesonotal declivity. Type specimens of P. flavens var. haytiana Forel were not examined for this study.
The only material from outside Central America and the Caribbean that we were able to confirm as matching the Wilson’s neotype was from Florida. The Florida populations referred to here as P. flavens and P. navigans are almost certainly heterospecific. We suspect that Nearctic records of P. flavens outside of Florida such as those reported from Louisiana (Colby and Prowell 2006; Dash and Hooper-Bùi 2008) refer to either P. bilimeki or the species we are treating as P. navigans in the southeastern USA.
The biology of Pheidole flavens, as currently conceived, was reviewed by Wilson (2003) with contributing observations by Jack Longino. The species prefers rotting wood, but also nest beneath the bark of trees, in dead knots on tree trunks, in sod on rocks, in the soil beneath stones, and in epiphyte masses. In the Caribbean it is recorded from forests and thickets from sea level to 900 m, and in Costa Rica it occurs in both wet and dry forests below 1000 m. The nest galleries are diffuse and irregular. Mature colonies are large containing up to thousands of workers. Workers collect small arthropods and will recruit to sugar baits.
Pheidole flavens (or at least it’s very close relatives) are easily transported long distances, and are known to hitchhike with fresh plant material (Wilson 2003). However, the species is not known to cause significant impact to agricultural systems or native ecosystems, and is not considered a house pest (Hedges 1998; Klotz et al. 1995).
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. Head punctate. Antennal scapes extend beyond posterior margin of head. Antennal scrobe lacking. Postpetiole not swollen relative to petiole. Hairs on mesosoma fine and flexuous, not arranged in pairs. Major worker characters. Antennal scrobe weakly to moderately impressed, but some depression capable of receiving antennal scapes clearly visible. Cephalic carinae approaching posterior head margin [requires additional analysis]. Posterolateral lobes distinctly rugose. Posterolateral portion of cephalic dorsum smooth and shining, lacking sculpture. Promesonotum in profile with one distinct convexity.
Diagnosis among introduced Pheidole. Color variable. Major | Head subquadrate (Fig. 7). Longitudinal carinae extend from anterior frons margin variable distance beyond frontal carinae, but never reach posterior head margin (Fig. 25). Rugae of posterolateral lobes variable from mostly absent, to predominantly longitudinal, to distinctly reticulated. Posterior head margin always free of distinct rugae (Fig. 25) or rugoreticulum (Fig. 27). Microsculpture of posterolateral lobes variable from glossy to moderately punctate. Hypostoma with stout median and submedian teeth. Promesonotal dorsum usually with distinct transverse striae (Fig. 21), but sometimes lacking distinct striae. Promesonotum in profile forming a single dome (Fig. 4), lacking a distinct mound or prominence on the posterior slope. Promesonotum not strongly transverse with strongly projecting sides in dorsal view (Fig. 29). Postpetiole not swollen relative to petiole (Fig. 3). Postpetiole relatively narrow in dorsal view; distinctly less than 2x petiolar width. Gaster with entire first tergite glossy (Fig. 32). Minor | Head covered in punctate microsculpture, giving it a dull appearance. Posterior portion of head lacking many short to medium length segments of striae distinctly interlaced among punctate ground sculpture. Antennal scapes often, but not always, surpass posterior head margin; if they do it is usually by a distance less than eye length. Antennal scapes with standing hairs present. Promesonotum in profile forming a single dome (Fig. 42), lacking a distinct mound or prominence on the posterior slope. Hairs on mesosoma fine and flexuous, not arranged in pairs. Pronotal humeri not angular. Postpetiole not swollen relative to petiole (Fig. 3). Postpetiole relatively narrow (Fig. 30); distinctly less than 2x petiolar width in dorsal view. Gaster with entire first tergite glossy (Fig. 32).
Pheidole navigans
Pheidole flavens is among the most widespread and abundant species of its genus in the New World, although this range might be representative of multiple cryptic species. As currently conceived, however, we consider P. flavens native from southern Mexico east through the Caribbean and south to Uruguay and northern Argentina. It is difficult to know whether the disjunction separating the western and eastern regions of South America is accurate or a sampling artifact. The Florida population is believed to have derived from an accidental introduction by commerce (Deyrup et al. 2000; Wilson 2003).