Pheidole rhinoceros

This species occurs in lowland wet forest habitats. Its upper elevational limit varies geographically: on the Barva Transect in Costa Rica it does not occur over 500m elevation. It occurs as high as 800m elevation in the Peñas Blancas Valley in the Cordillera de Tilarán, and it has been collected at 1100m on Volcan Cacao, an isolated peak in the Cordillera de Guanacaste. Nests are in dead wood on the forest floor, under loose bark, and occasionally in live stems (nests have been collected in live stems of Myriocarpa [Urticaceae] and the petiolar domatia of Piper cenocladum [Piperaceae]). Surprisingly, given the moderately common discovery of nests when general collecting, workers rarely recruit to baits and are rarely collected in Winkler or Berlese samples. (Longino 2009)

Identification
See the notes from Longino in the nomenclature section.

Distribution
Panama to southern Mexico.

Distribution based on Regional Taxon Lists
Neotropical Region: Colombia, Costa Rica, Honduras, Mexico, Nicaragua, Panama.

Nomenclature

 *  rhinoceros. Pheidole rhinoceros Forel, 1899c: 73, pl. 3, fig. 23 (s.w.) PANAMA. See also: Wilson, 2003: 738.

Longino (2009) - Two similar species have been conflated under this name until now. Wilson (2003) examined the lectotype of P. rhinoceros but later used specimens of the similar Pheidole rhinomontana for illustrations. See further discussion and diagnostic characters under P. rhinomontana. Pheidole unicornis Wilson 2003 is not currently separable from P. rhinoceros, but I defer synonymy pending additional study. In Central America, P. rhinoceros is a lowland species and P. rhinomontana is a parapatric replacement species at higher elevations. Unlike this pattern, P. unicornis has the morphology of P. rhinoceros but was collected at 2100m near Cali, Colombia. The minor workers appear somewhat more robust than the typical P. rhinoceros from Costa Rica.

Description
From Wilson (2003): DIAGNOSIS Similar in various ways to Pheidole binasifera, Pheidole diabolus, Pheidole gravida, Pheidole mirabilis, Pheidole moseni, Pheidole mosenopsis, Pheidole nasifera, Pheidole unicornis, differing as follows.

Major: middle carina of clypeus raised into a right-angular hornlike protrusion, from which radiate carinulae traveling obliquely downward toward the anterior clypeal border; carinae originating on borders of frontal lobe curve inward toward the midline; posterior half of dorsal surface and all of pronotum smooth and shiny; propodeal spines slender, and vertical on the propodeal basal face.

Minor: propodeal spines short, slender, and vertical on the propodeal basal face; head entirely smooth. Longino (1997) notes that considerable variation exist in the sculpturing of the minors in at least Honduras and Costa Rica. At elevations of about 500 m or higher, minors tend to have more extensive foveolation on the pronotum and mesopleuron than do minors at lower elevations. In Costa Rica at least, the two forms are nowhere sympatric but in Braulio Carrillo National Park approach within 300 m elevation and about 5 km distance. The two forms may represent distinct species, but Longino treats them as conspecifics, and this more conservative arrangement appears appropriate for the time being.

MEASUREMENTS (mm) Lectotype major: HW 1.26, HL 1.40, SL 0.60, EL 0.16, PW 0.70. Paralectotype minor: HW 0.60, HL 0.64, SL 0.58, EL 0.10, PW 0.38.

COLOR Major and minor: concolorous light to medium brown.

Type Material
Longino (2009) - Lectotype major worker (here designated, as labeled by Wilson 2003) and associated paralectotype minor worker: Panama, Bugaba, 800–1500ft (Champion) [] (examined).

Etymology
Species name inspired by the hornlike extension of the midclypeus. (Wilson 2003)