Pheidole arachnion

Workers, minors and majors, can be moderately abundant in Winkler or Berlese samples of forest floor litter but are rarely collected at baits. The lack of occurrence at baits suggests largely nocturnal foraging or foraging restricted to areas beneath litter or in rotten wood. One nest is known, from rotten wood on the forest floor. (Longino 2009)

Identification
See the description in the nomenclature section.

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

Habitat
This species occurs in wet forest habitats, from sea level to 1100m elevation.

Worker
Minor

Nomenclature

 *  arachnion. Pheidole arachnion Wilson, 2003: 656, figs. (s.w.) COSTA RICA. Senior synonym of iradunca: Longino, 2009: 13.
 * iracunda. Pheidole iracunda Wilson, 2003: 712, figs. (s.w.) COSTA RICA. Junior synonym of arachnion: Longino, 2009: 13.

Description
DIAGNOSIS A member of the tristis group characterized by the following combination of traits.

Major: dark reddish brown; sides of head covered by loose rugoreticulum (i.e. with large interspaces); humeri and postpetiolar nodes seen from above comulate (hom-shaped); lacking any trace of antennal scrobes.

Minor: propodeal spine reduced to an obtuse angle; body entirely smooth and shiny except for several carinulae on anterior half of dorsal surface of head, one of which loops on each side of the head in a semicircle from the end of the frontal lobe to the anterior clypeal border; a thin nuchal collar present.

Very similar to Pheidole iracunda, also of Costa Rica, but differing in details in the characters as listed and illustrated.

MEASUREMENTS (mm) Holotype major: HW 1.80, HL 1.98, SL 0.76, EL 0.18, PW 0.90. Paratype minor: HW 0.60, HL 0.62, SL 0.74, EL 0.10, PW 0.40.

COLOR Major: body and mandibles dark reddish brown, other appendages light reddish brown. Minor: body plain medium brown, appendages brownish yellow.



'''Figure. Upper: holotype, major. Lower: paratype, minor. Scale bars = 1 mm.'''

Type Material
COSTA RICA: Rio Reventazon, 3-5 km east of Turrialba, Cartago, col. William L. Brown.

Longino (2009) - Pheidole iracunda Wilson, 2003: 712, figs. Holotype major worker and associated paratype minor worker: Costa Rica, Prov. Heredia, La Selva Biological Station (Cover, Moffett, Tobin) MCZ (examined).

Etymology
Gr arachnion, cobweb, alluding to the loose rugoreticulum on the head of the major.

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. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/