Pheidole fossimandibula

This species inhabits mature wet forest from sea level to 800m elevation. Minor workers are relatively common and are frequently collected in Winkler samples, at baits, and in Malaise traps. (Longino 2009)

Identification
With the morphometric profile and general habitus of Pheidole bigote and Pheidole vestita. Minor worker: transverse carina on anterior pronotum small and inconspicuous versus developed as a prominent flange visible in side view (bigote); mandible with basal portion roughened versus completely smooth and shining (vestita); katepisternum and side of propodeum faintly foveolate and lacking rugulae versus with irregular rugulae overlaying foveolate sculpture (bigote) or with irregular rugulae (vestita). Major worker: mandible with a broad concavity covering basal half of dorsal surface versus dorsal surface flat to weakly convex (bigote, vestita). (Longino 2009)

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica.

Biology
Longino (2009) - Two nests were excavated in close proximity. The nests were located by following minor workers from baits to nest entrances. The nest entrance was a simple hole in the ground, with no superstructure. One excavation reached 10-15cm depth, uncovering two or three chambers with brood, minor workers, and major workers. The second excavation was 12cm deep, uncovering two chambers, one shallower and one at 12cm, also with brood, minors, and majors. No reproductives were found, and it is possible that the nests continued deeper than the zone of excavation. No seeds were found in the uncovered chambers.

The major workers have never been observed leaving the nest and their function in the colony is unknown. Prior to excavating one of the above nests a live Aphaenogaster worker was pinned to the ground at the nest entrance. Some minor workers immediately attacked and there was increased activity around the entrance, but after 5 minutes no majors had recruited, and upon excavation I found majors only in the deepest chambers.

Worker
Minor

Images from AntWeb
Major

Nomenclature

 *  fossimandibula. Pheidole fossimandibula Longino, 2009: 33, fig. 7 (s.w.) COSTA RICA.

Worker
Minor Measurements (paratype): HL 0.78, HW 0.70, HLA 0.30, SL 0.69, EL 0.15, ML 0.93, PSL 0.03, PMG 0.00, SPL 0.03, PTW 0.12, PPW 0.16, CI 90, SI 99, PSLI 4, PMGI 0, SPLI 4, PPI 135.

Measurements (n=10): HL 0.63-0.78, HW 0.60-0.70, SL 0.62-0.69, CI 90-94, SI 99-105.

Mandible with faint rugulose-foveolate sculpture on base of dorsal surface, grading to smooth and shiny at masticatory margin; clypeus smooth and shining; face with about four widely-spaced concentric rugae around antennal insertion, rest of face smooth and shining; posterior margin of vertex somewhat flattened; occipital carina narrow, visible in full face view; scape faintly foveolate, with abundant erect setae longer than maximum width of scape; promesonotum smoothly arched with no trace of promesonotal groove; propodeal spines very short, upturned; promesonotum and anepisternum smooth and shining; katepisternum and lateral and dorsal faces of propodeum generally shining with faint foveolation; abundant setae on promesonotal dorsum; dorsal (outer) margin of hind tibia with abundant suberect setae longer than maximum width of tibia; first gastral tergum smooth and shining; gastral dorsum with moderately abundant, long erect setae; color dark red brown.

Major Measurements (holotype): HL 2.24, HW 1.73, HLA 0.58, SL 0.74, EL 0.22, ML 1.68, PSL 0.11, PMG 0.00, SPL 0.07, PTW 0.33, PPW 0.52, IHT 0.36, OHT 0.62, CI 77, SI 43, PSLI 5, PMGI 0, SPLI 3, PPI 155, HTI 58.

Mandible smooth and shining, with broad concavity covering basal half of dorsal surface, basal margin forming a narrow ridge covered with dense long decumbent yellow setae; clypeus with two median gibbosities, gibbosities and lateral clypeus covered with dense piligerous puncta and long orange-yellow setae that sweep forward and medially, midline of clypeus concave, smooth and shining; frontal carinae forming elevated triangular lamina anteriorly, slanting obliquely outward posteriorly, forming dorsal margins of prominent antennal scrobes, ventral margin of scrobe formed by strong carina, scrobe surface smooth and shining, space between scrobe, compound eye, and clypeus with coarse, widely-spaced carinae; area between frontal carinae smooth and shining, grading to widely-spaced arcuate to reticulate rugae on vertex lobes; face covered with dense erect yellow setae, becoming denser and longer on anterior face and clypeus, in lateral view forming a conspicuous yellow brush anteriorly; head with abundant erect setae projecting from sides of head in face view; scape microsculptured and dull, not shining, somewhat flattened at base but not broadened, narrower than width at apex, with abundant erect setae longer than maximum width of scape; hypostomal margin straight; median tooth small; inner hypostomal teeth pointed, stout, about one half distance from midline to outer hypostomal teeth; promesonotal groove absent; propodeal spines present; mesosoma largely smooth and shining, with sparse small carinulae; dorsal (outer) margin of hind tibia with abundant suberect setae longer than maximum width of tibia; pilosity abundant on mesosomal dorsum; postpetiole in dorsal view strongly lenticular, much broader than long; first gastral tergite with small patch of longitudinal etched microsculpture near postpetiolar insertion, smooth and shining elsewhere, with abundant long erect yellowish setae; color dark red brown.

Type Material
Holotype major worker. Costa Rica, Alajuela: Casa Eladio, Rio Peñas Blancas, 10.31667°N 84.71667°W, ±2000m, 800m, 3 Mar 2008 (J. Longino#6156), unique specimen identifier CASENT0608928.

Paratypes: major and minor workers. Same data as holotype, , EAPZ, ECOSCE, , , , , , , , , MEL, , ICN,.

Etymology
The name is in reference to the depression on the dorsal surface of the mandible of the major worker.

References based on Global Ant Biodiversity Informatics

 * Longino J. T. 2009. Additions to the taxonomy of New World Pheidole (Hymenoptera: Formicidae). Zootaxa 2181: 1-90.
 * Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.
 * Longino J. T., and R. K. Colwell. 2011. Density compensation, species composition, and richness of ants on a neotropical elevational gradient. Ecosphere 2(3): 16pp.