Subfamily FORMICINAE
Tribe FORMICINI

Polyergus montivagus Wheeler 1915

by Joe A. MacGown, uploaded 20 August 2014

Polyergus montivagus, full face view of a worker (photo by James Lewis and Joe MacGown)
Polyergus montivagus, profile view of a worker (photo by James Lewis and Joe MacGown)
Polyergus montivagus, 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 montivagus is an average sized, somewhat shiny, reddish-brown species with sparse to no erect hairs on head and mesosoma that uses Formica pallidefulva as a host.

Taxonomic History (from Trager 2013, Bolton 2014)
Polyergus lucidus montivagus Wheeler 1915: 419. Syntype workers, gyne, male.
Polyergus lucidus: Creighton, 1950 (incorrect synonymy).

Identification
Worker Measurements (in mm) from Trager 2013 (for more comprehensive measurements, see Trager's paper). (N=32) HL 1.40–1.70 (1.55), HW 1.40–1.68 (1.51), SL 1.34–1.58 (1.44), WL 2.28–2.76 (2.46), TL 5.68–7.16 (6.28). Color, orangish-red, apex of gaster lacking or with only weak infuscation, appendages slightly darker than body. Head and mesonotum weakly shining, pronotum shiny (laterally), and gaster shining. Head about as wide as long, truncate anteriorly and ovoid posteriorly, cheeks slightly concave, sides of head converge above eyes, posterior border mostly straight to feebly emarginate; vertex with 0–2 erect setae near each corner. Scape reaching or surpassing vertex corners and thickened apically. Pronotum with 0–2 erect setae (up to 5 in some specimens); mesonotum weakly convex in profile; propodeum in profile rounded right angle; petiole relatively low, 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).

This species can be separated from P. longicornis by its lack of infuscation at the apex of gaster and lack of erect hairs on the vertex, unlike P. longicornis, which has gastral infuscation and numerous erect setae present on vertex. Additionally, P. montivagus uses Formica as a host, whereas P. longicornis uses F. pallidefulva. It differs from P. lucidus in that the head and alitrunk are subopaque, whereas, in P. lucidus, the entire body is shining. Polyergus montivagus differs from P. mexicanus by having much longer scapes, scapes in P. mexicanus are not as long as interocular distance; by not having the antennal scapes terminating in a club (scapes in P. mexicanus enlarged distally forming a club); and by having sparse pubescence on the gaster, whereas, pubescence on gaster of P. mexicanus is dense).

Biology and Economic Importance
Polyergus montivagus typically nest in meadows with wooded borders, lawns and park-like habitats with scattered trees, and similar habitats where the host, F. pallidefulva, also nests. This species is only known to use to utilize Formica pallidefulva as a host (King and Trager, 2007, Trager 2013). Raids on nests of the host F. pallidefulva have been observed to occur from mid Juine through September during the late afternoon until dusk.

This species poses little in the way of economic importance, as is rarely encountered. However, if provoked or handled a worker could inflict a somewhat painful bite.

Distribution (from Trager 2013 and MEM records)
USA: Colorado, Florida, Illinois, Iowa, Michigan, Mississippi, Nebraska, New York, Wisconsin.

CANADA: Ontario.

This species has been reported from Colorado and Florida (King and Trager, 2007; Smith, 1947), and it has been collected In Mississippi in Chickasaw, Lowndes, and Oktibbeha Counties (MEM records).

Literature Cited
Creighton, W. S. 1950. The ants of North America. Bulletin of the Museum of Comparative Zoology 104:1-585.

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

Smith, M. R. 1947. A Study of Polyergus in the United States, based on the workers (Hymenoptera: Formicidae). The American Midland Naturalist 38: 150-161.

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

Wheeler, W. M. 1915. Some additions to the North American ant-fauna. Bulletin of the American Museum of Natural History 34:389-421.

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