Pheidole williamsi

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Pheidole williamsi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Pheidole
Species: P. williamsi
Binomial name
Pheidole williamsi
Wheeler, W.M., 1919

Pheidole williamsi casent0173597 profile 1.jpg

Pheidole williamsi casent0173597 dorsal 1.jpg

Specimen labels


Males were collected with the lectotype series in November 1905. (Wilson 2003)


See the description in the nomenclature section.

Keys including this Species


Only known from the Known only from Isla Santa Cruz, Isla Seymour, and Isla San Salvador. An apparent endemic of the Galápagos Islands. The species appears to be rare. (Wilson 2003)

Distribution based on Regional Taxon Lists

Neotropical Region: Ecuador, Galapagos Islands (type locality).

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.


Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.



Associations with other Organisms


This species is a host for the fungus Myrmicinosporidium durum (a pathogen) in Galapagos Islands (Espadaler, 1997).








The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

  • williamsi. Pheidole williamsi Wheeler, W.M. 1919c: 267 (s.w.q.m.) ECUADOR (Galapagos Is). Senior synonym of seymourensis: Wilson, 2003: 249.
  • seymourensis. Pheidole williamsi var. seymourensis Wheeler, W.M. 1924a: 108 (s.w.) ECUADOR (Galapagos Is). Junior synonym of williamsi: Wilson, 2003: 249.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.


From Wilson (2003): A small, yellow member of the diligens group, closest to Pheidole crozieri of Peru, but also with some similarities to Pheidole vafella, as well as Pheidole rufipilis and the mostly South American species listed with rufipilis (q.v.), differing from crozieri as follows.

Major: dark yellow; pronotum in side view peaked in a blunt angular profile, and weakly bilobous in dorsal-oblique view; occiput weakly concave; anterior margin of pronotal dorsum carinulate; apex of petiolar node in side view tapering to a blunt point.

Minor: petiolar node in side view relatively low, and in rear view with dorsal border strongly convex.

MEASUREMENTS (mm) Lectotype major: HW 1.04, HL 1.10, SL 0.74, EL 0.16, PW 0.52. Paralectotype minor: HW 0.48 (approximately), HL 0.62, SL 0.66, EL 0.12, PW 0.30.

COLOR Major: concolorous dark yellow.

Minor: body brownish yellow, appendages dark to medium yellow.

The Wheeler types may be faded; minors collected on Isla San Salvador in 1991 (P. Oromi) have light brown bodies.

Pheidole williamsi Wilson 2003.jpg

Figure. Upper: lectotype, major. Lower: paralectotype, minor. Scale bars = 1 mm.

Lectotype Specimen Labels

Type Material

GALÁPAGOS ISLANDS: Isla Santa Cruz. Museum of Comparative Zoology - as reported in Wilson (2003)


Named after Harrison Williams, leader of a Galápagos collecting expedition. (Wilson 2003)


References based on Global Ant Biodiversity Informatics

  • Clark, David B., Concepcion Guayasamin, Olga Pazmino, Cecilia Donoso, Yolanda Paez de Villacis. 1982. The Tramp Ant Wasmannia auropunctata. Biotropica. 14 (3):196-207.
  • Herrera H. W. 2013. CDF Checklist of Galapagos Ants - FCD Lista de especies de Hormigas Galápagos. In: Bungartz, F., Herrera, H., Jaramillo, P., Tirado, N., Jiménez-Uzcátegui, G., Ruiz, D., Guézou, A. & Ziemmeck, F. (eds.). Charles Darwin Foundation Galapagos Species Checklist - Lista de Especies de Galápagos de la Fundación Charles Darwin. Charles Darwin Foundation / Fundación Charles Darwin, Puerto Ayora, Galapagos: Last updated: 01 Mar 2013
  • Herrera H.W., and L. Roque-Albelo. 2007. Lista anotada de las hormigas de las Islas Galapagos, Ecuador. Fundación Charles Darwin. 13 pp
  • Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
  • Kusnezov N. 1963. Zoogeografia de las hormigas en sudamerica. Acta Zoologica Lilloana 19: 25-189
  • Kusnezov N. 1963. Zoogeografia de las hormigas en sudamerica. Acta Zoologica Lilloana 19: 25-190
  • Linsley E. G., and R. L. Usinger. 1966. Insects of the Galápagos Islands. Proc. Calif. Acad. Sci. (4) 33: 113-196.