Subfamily FORMICINAE
Tribe FORMICINI

Polyergus oligergus Trager

by Joe A. MacGown, uploaded 20 August 2014

Polyergus oligergus, full face view of a worker (photo by James Lewis and Joe MacGown)
Polyergus oligergus, profile view of a worker (photo by James Lewis and Joe MacGown)
Polyergus oligergus, dorsal view of a worker (photo by James Lewis and Joe MacGown)

Overview
Polyergus workers can be easily recognized by their large size (approximately 4.0 - 7.7 mm long), yellowish-red to dark reddish-brown coloration, distinct promesonotal suture, three small ocelli, and sickle-shaped (falcate) mandibles with minute serrations on the inner borders.

Polyergus species are obligatory or true slave-making ants. In nest founding, the female enters a nest of the host species, eventually kills the rightful queen, and uses the host workers to tend her brood. Polyergus colonies conduct slave raids on nests of various species of Formica, and workers of the host are taken and used by the Polyergus colony to feed and rear the brood and excavate the nest. Polyergus workers are incapable of surviving without slaves. In laboratory colonies, a colony without slaves will starve to death even when plentiful food is available. (Hedlund, 2007; King and Trager, 2007).

Polyergus oligergus is a smallish reddish-brown species only known to occur in Florida where it uses Formica archboldi as a host.

Taxonomic History (from Trager 2013, Bolton 2014)
Polyergus oligergus Trager, 2013: 527 (w.) U.S.A. Nearctic.

Identification
Worker Measurements (in mm) from Trager 2013 (for more comprehensive measurements, see Trager's paper). (N=44) HL 1.32–1.66 (1.48), HW 1.28–1.63 (1.45), SL 1.40–1.61 (1.51), WL 2.09–2.68 (2.36), TL 5.23–6.94 (5.96). Color red (reddish-brown) with legs slightly darker. Head and mesonotum weakly shining, but shiner on lateral part of pronotum, and gaster shiny. Head ovate to subhexagonal, widest behind eyes (posterior to eyes), almost as wide as long, and with sides slightly concave; vertex with 2–5 macrosetae near each corner; scapes surpass vertex corners and are gradually thickened apically. Pronotum with 1–4 erect setae. Mesonotum weakly convex in profile. Propodeum in profile fournded with doral and posterior faces meeting in almost a curved right angle. Petiole low in profile with rounded sides, flat dorsum (or weakly concave), sides converging dorsally, with anterior surface in profile slightly convex and posterior face in profile straight. First tergite lacking pubescence and with few to no erect macrosetae (0–6).

Polyergus oligergus is most similar to P. montivagus, but differs by being smaller, having more macrosetae on vertex, and being associated with only Formica archboldi.

Biology and Economic Importance
Polyergus oligercus is only known to occur in Florida where it uses Formica archboldi as a host. Colonies are relatively small. Raids have been observed at approximately 6 PM from mid-May through July (one raid was observed in September, which appeared to be atypical) (Trager 2013, Trager and Johnson 1985). Alates were observed flying from nests between 11:00 AM and noon on dry, clear days in July by Trager and Johnson (1985)

Distribution (from Trager 2013)
USA: Florida

Literature Cited
Hedlund, K. S. 2007. The Ants: North America Catalog: Genus Polyergus. http://www.cs.unc.edu/~hedlund/playpen/dev/ants/catalog/ (accessed 6 June 2008).

King, J. R. and J. C. Trager. 2007. Natural history of the slave making ant, Polyergus lucidus, sensu lato in northern Florida and its three Formica pallidefulva group hosts. 14 pp. Journal of Insect Science 7: 42, available online: insectscience.org/7.42

Trager, J. C. 2013. Global revision of the dulotic ant genus Polyergus (Hymenoptera: Formicidae, Formicinae). Zootaxa 3722 (4): 501–548.

Trager, J.C. & Johnson, C. (1985) A slave-making ant in Florida: Polyergus lucidus with observations on the natural history of its host
Formica archboldi (Hymenoptera: Formicidae). Florida Entomologist, 68, 261–266.

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