Subfamily FORMICINAE
Tribe FORMICINI

Polyergus longicornis Smith 1947

by Joe A. MacGown, uploaded 21 July 2009, updated 7 August 2014

Polyergus longicornis, full face view of a worke
Polyergus longicornis, profile view of a worke
Polyergus longicornis, full face view of a worker (photo by James Lewis and Joe MacGown)
Polyergus longicornis, profile view of a worker (photo by James Lewis and Joe MacGown)
Polyergus longicornis, dorsal view of a worker (photo by James Lewis and Joe MacGown)
Polyergus longicornis, full face view of a queen
Polyergus longicornis, full face view of a queen (photo by James Lewis and Joe MacGown)
Polyergus longicornis, profile view of a queen (photo by James Lewis and Joe MacGown)
Polyergus longicornis, dorsal view of a queen (photo by James Lewis and Joe MacGown)
Polyergus longicornis, raiding Formica dolosa colony on 8 June 2008 in Sturgis, MS
Polyergus longicornis, raiding Formica dolosa colony on 8 June 2008 in Sturgis, MS
Polyergus longicornis, raiding Formica dolosa colony on 8 June 2008 in Sturgis, MS
Polyergus longicornis, workers carrying Formica dolosa brood on 8 June 2008 in Sturgis, MS
Polyergus longicornis, raiding Formica dolosa colony on 8 June 2008 in Sturgis, MS
Polyergus longicornis, raiding Formica dolosa colony on 8 June 2008 in Sturgis, MS

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 sture, 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 longicornis is a matte, reddish colored species known only from the southeastern US where it uses Formica dolosa as its host.

Common Name
Slave making ant

Taxonomic History (from Trager 2013, Bolton 2014)
Polyergus lucidus subsp. longicornis Smith, 1947: 155 (w.) U.S.A. Nearctic. Raised to species: Trager, 2013.

Identification
Worker: Measurements (in mm) from Trager 2013 (for more comprehensive measurements, see Trager's paper). (N=18) HL 1.60–1.80 (1.71), HW 1.52–1.72 (1.62), SL 1.67–1.89 (1.77),WL 2.52–2.88 (2.73),TL 6.44–7.32 (6.78).Color reddish-brown with appendages and posterior parts of tergites infuscated. Head and mesosoma opaque, not shiny, gaster weakly matte. Head slightly longer than wide, truncate-obovate; cheeks slightly concave; sides of head converging above eyes; vertex (occipital) border feebly emarginate; vertex with 20–40 erect setae. Eye convex, longer than wide, situated more than its greatest diameter from the mandibular base. Antennal scape long, 1.5 times length of interocular distance, at least as long as head length to obviously longer, always surpassing corners of vertex, and gradually enlarged apically. Pronotum with 6–12 erect setae; mesonotum flat to weakly convex in profile; propodeum evenly rounded in profile with indistinct dorsal and posterior faces. Petiole slightly narrower than propodeum, with sides convex and converging dorsally; dorsum of petiole convex, not emarginate; in profile, petiole slightly tapering and curving posteriorly. First gastral tergite lacking or with sparse pubescence; first tergite with sparse weakly flexuous macrosetae anteriorly.

Polyergus longicornis is most similar to P. ruber, but can be distinguished by it greater abundance of setae on the vertex, matte head and mesosoma, and its parastism of F. dolosa instead of F. biophilica. This species can be separated from P. montivagus by its longer antennal scapes, which are more than 1.45 times as long as the interocular distance in P. longicornis, but less than 1.4 times as long in P. montivagus; by its infuscation at the apex of gaster and presence of numerous erect hairs on the vertex corners, both of which are lacking in P. montivagus (1 or 2 erect hairs may be present on each of the vertex corners of P. montivagus). It can be distinguished from P. lucidus by its long antennal scapes, which in P. longicornis are less than 1.4 times as long as the interocular distance in P. lucidus; in P. longicornis, the head and alitrunk are subopaque, whereas, in P. lucidus, the body is shining. Polyergus longicornis 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. breviceps is dense).

Biology and Economic Importance
As with other Polyergus species, P. longicornis are obligate slave-makers. This species is only known to be associated with Formica dolosa, a common species in woodland areas in the Southeast. Nests are inconspicuous and often difficult to find in our area and may be located at bases of trees or other smaller plants underneath leaf litter. The easiest way to find a colony is to observe a raiding column and follow it back to the nest. Raids appear to be conducted throughout the summer months, and in all observations that I have made or have had information about, the raids took place in late afternoon at approximately 5:00 to 6:00 PM. In fact, you could set your watch by their raids, as any particular colony we have observed always performed their raids at the same time each day. Raids are efficient, and start with numerous P. longicornis workers emerging from a mixed colony (P. longicornis/F. dolosa). After first exiting the colony, the Polyergus workers mill about in an apparent frenzied state before suddenly becoming organized into a column about 12 to 15 cm wide and 3 m long. In my observations, all of the ants that exited the colony were involved in the march, but this only represented a fraction of the colony, as when the nest was slightly disturbed, many other workers emerged. Once the column is formed, the ants march with singular intent toward their goal. In some cases, they may become disoriented if something in the landscape has changed since their initial finding of the Formica colony, at which point they regroup together in a large somewhat circular pattern until they regain the "trail" and reform their column. The column does not deviate from the trail, even if various obstacles are in the way, such as logs, flower pots, etc., they simply climb over them and continue. They may travel several to many meters until reaching the Formica nest. Upon reaching the Formica nest, which in our area is generally inconspicuous, the Polyergus workers immediately enter the Formica colony and very quickly reappear from the colony carrying either a single pupa in a cocoon or a larva in their mandibles, which are perfectly designed for carrying cocoons and larger larvae.  Formica workers also emerge from the colony, milling about in apparent agitation.  Occasionally, Formica workers attempt to thwart Polyergus workers from plundering their brood by holding on to the immature ant as the Polyergus tries to carry it away.  However, in all cases that I have observed, the Formica worker relinquished its hold after a few seconds and the Polyergus worker joined its fellow workers in the column for the return trip to their colony.  During these raids, workers from the two colonies do not typically attack one another.  Raids on Formica colonies are extremely methodical and typically only last a few minutes.  After capturing the young ants, the Polyergus workers immediately head back to their colony in column formation.  When they arrive at their colony, they immediately enter the nest.  During this time, Formica workers from the Polyergus colony can be seen exiting the colony and moving freely among the Polyergus workers.  After all of the Polyergus workers enter the colony, several Formica workers stay above ground in the vicinity of the colony.  These workers are aggressive and will readily attack if provoked. Likewise, upon happening upon a Polyergus/Formica colony while randomly sifting leaf letter, I have found Polyergus workers to be extremely belligerent, wasting little time in attacking and biting. Their large sickle-shaped mandibles may not be good for such mundane tasks as eating and building, but they are extremely effecting for piercing human skin!

Although colonies of the host species F. dolosa, are extremely common in open wooded habitats in the Southeast, especially in upland areas, colonies of P. longicornis are rarely encountered. This is not just a factor of luck in finding colonies either, because for any given colony of P. longicornis to thrive for an extended period of time, it would require many colonies of F. dolosa to support it. Completely eliminating the brood from a single Formica colony could potentially cause the demise of that Formica colony, or, at the very least, brood would not be available for the Polyergus colony until the Formica colony had time to replenish. Therefore, it would seem likely that a single Polyergus colony would need multiple Formica colonies to exist. Indeed, based on the observations of a local resident in Sturgis, Oktibbeha County, MS, Polyergus colonies were seen raiding for many continuous days throughout the summer and usually raiding different Formica colonies each time. Additionally, one observer noted that "their" colony persisted for at least three years, although at one point in time, it relocated the colony location.

Alates of this specie have been collected in the summer.

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

Distribution
This species has been reported from Florida, Georgia, Mississippi, North Carolina, and South Carolina (Hill and Brown, 2005; King and Trager, 2007; MacGown and Brown, 2006; Smith; 1979; Trager, 2013]. In Mississippi, it has been collected from George, Oktibbeha, Pontotoc, and Winston Counties.

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).

Hill, J. G. and R. L. Brown. 2005. The first record of the genus Polyergus (Hymenoptera: Formicidae) in Mississippi [Abstract]. Journal of the Mississippi Academy of Sciences 50: 120.

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

MacGown, J. A. and  R. L. Brown. 2006. Survey of Ants (Hymenoptera: Formicidae) of the Tombigbee National Forest in Mississippi.  Journal of the Kansas Entomological Society.  79: 325-340.

Smith, D. R. 1979.  In Catalog of Hymenoptera in America north of Mexico. Smithsonian Institution Press, Washington D. C.  Vol. 2, pp. 1323-1427. 

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.

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