Polyergus bicolor

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Polyergus bicolor
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Formicinae
Tribe: Formicini
Genus: Polyergus
Species group: rufescens-breviceps
Species: P. bicolor
Binomial name
Polyergus bicolor
Wasmann, 1901

Polyergus bicolor casent0179561 p 1 high.jpg

Polyergus bicolor casent0179561 d 1 high.jpg

Specimen Labels

This species lives in rotting logs, possibly preferring pine, with its host Formica subaenescens or less commonly Formica neorufibarbis (James Trager).

At a Glance • Slave-maker  

 

Identification

P. bicolor is usually easily distinguished from other Nearctic species by its distribution, distinctive two-tone coloring and sparse pilosity. Northern (North Dakota, USA to British Columbia, Canada) populations of Polyergus mexicanus may exhibit similar coloration, but mexicanus is always more pilose. Bicoloration and reduced pilosity occur commonly in the small workers from young colonies of mexicanus, causing possible confusion. Nanitics of mexicanus are usually recognizable by their slender heads with a rounded vertex and longish appendages, and at least a pair of erect pronotal setae. Large workers of other breviceps-complex species also may appear somewhat bicolored, but only rarely is the bicoloration so neatly defined by a nearly completely dark gaster as in bicolor, and these others have more pilosity on the head and mesosoma.

Keys including this Species

Distribution

This species is apparently endemic to the upper Mississippi Valley, from the western Great Lakes region west to the Dakotas and southern Manitoba. In the past it was found in southern Wisconsin and as far south as Rockford, Illinois, but it has not been seen in this area in recent decades.

Distribution based on Regional Taxon Lists

Nearctic Region: Canada, United States (type locality).


Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Trager (2013): P. bicolor normally parasitizes Formica subaenescens, and normally nests with it in rotten stumps or fallen limbs in forests. Wheeler (1910) described raids occurring in early afternoon in a mature mesic forest in northern Illinois that originated from nests in stumps. Two samples examined in this study had Formica neorufibarbis hosts, also a denizen of moist woods, especially tamarack bogs in the eastern part of its range. Through the course of this study I was not able to obtain or study any specimens of bicolor (nor of its host F. subaenescens) collected within about the last 50 years, from bicolor’s historic range, and I am led to wonder if they have contracted northward due to climatic warming or other causes. Just before submitting this manuscript, in July 2013, I collected a sample in northern Wisconsin. As in the published records, this sample occupied a rotting log with F. subaenescens. The log was about 35 cm in diameter, with bark beginning to loosen and wood in transition from white to red rot. At first glance, the mixed colony bore a striking resemblance to a young colony of the locally common Formica aserva.

Castes

Worker

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • bicolor. Polyergus rufescens subsp. bicolor Wasmann, 1901: 369 (w.q.m.) U.S.A. Junior synonym of breviceps: Wheeler, J. 1968: 163. Raised to species: Trager, 2013: 514.

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

Type Material

Polyergus rufescens subsp. breviceps var. fusciventris Wheeler 1917: 555 (part). Unavailable name; following material referred here: CANADA, MANITOBA, South Cypress RM. Treesbank. (Wheeler) [USNM #59925, USNM ENT 00529453] (image examined by Trager, 2013).

Description

Worker

Trager (2013) - Syntype [LACM, red “type series” label, top specimen] HL 1.30, HW 1.28, SL 1.04, ½ VeM 0, ½ PnM 0, WL 1.96, GL 1.88, HFL 1.48, CI 98, SI 81, HFI 116, FSI 142, LI 3.26, TL 5.14.

(N=44) HL 1.24–1.66 (1.40), HW 1.24–1.74 (1.41), SL 0.92–1.16 (105), ½ VeM 0, ½ PnM 0–2 (0.58), WL 1.88–2.32 (2.08), GL 1.60–2.80 (2.07), HFL 1.40–1.68 (1.55), CI 97–105 (100), SI 64–81 (75), HFI 97–120 (110), FSI 137–158 (147), LI 3.12–3.98 (3.48), TL 4.83–6.58 (5.56).

Head subquadrate to suborbicular, its length and breadth about equal, sides often quite rounded; vertex concave, the concavity about half the head width in breadth, completely lacking vertex pilosity; scapes short, not reaching vertex corners, notably clavate in the apical third; pronotum lacking pilosity, or rarely with 1–2 dorsal erect setae; mesonotum profile flat or very weakly convex for most of its length; propodeum profile a rounded weakly obtuse angle; petiole with rounded sides, petiolar dorsum rounded, not at all or only feebly emarginate; first tergite moderately pubescent, with pilosity much like that of breviceps, in 4–5 transverse arrays; first tergite pilosity flexuous, subdecumbent.

Head matte; mesonotum matte; gaster matte to weakly shining.

Color of head, mesonotum and often petiole dull red, gaster very dusky red (nearly black); forelegs often redder than middle and hind legs; pilosity reddish brown, pubescence fine and grayish.

Etymology

Trager (2013) - Wasmann coined this name from the Latin nominal adjective “bicolor” meaning two-colored.

References