Subfamily FORMICINAE
Tribe FORMICINI

Polyergus longicornis Smith
Polyergus longicornis, full face view of a worker
Polyergus longicornis, a profile view of worker
Polyergus longicornis, full face view of a worker
(click image to enlarge).
Polyergus longicornis, a profile view of worker.
(click image to enlarge).
Polyergus longicornis, full face view of a worker
Polyergus longicornis, profile view of a worker
Polyergus longicornis, full face view of a worker (click image to enlarge).
Photo courtesy of http://www.antweb.org/
Polyergus longicornis, profile view of a worker (click image to enlarge).
Photo courtesy of http://www.antweb.org/
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
(click image to enlarge).
Polyergus longicornis, raiding Formica dolosa colony on 8 June 2008 in Sturgis, MS
(click image to enlarge).
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
(click image to enlarge).

Overview
Polyergus workers can be easily recognized by their large size (approximately 4.0 - 7.0 mm long), yellowish-red to dark reddish-brown coloration, and possession of sickle-shaped (falcate) mandibles with minute serrations on inner border.

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)

Common Name
Slave making ant

Identification
Overall length approximately 7.0 mm. Color, dull reddish-brown with third-fifth segments of gaster infuscated dark brown, appendages slightly darker than body. Head and alitrunk subopaque. Head 1.06 times longer than wide, cheeks slightly concave, sides of head converge above eyes, occipital border feebly emarginate. 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, and gradually enlarged as toward the apex (but not club-like as in P. breviceps). Frontal carina short, frontal area triangular, weakly defined. Ocelli small. Clypeus twice as wide as long or more, subcarinate, anterior border broadly emarginate medially. Mandible falcate, flattened and with minute serrations along inner border.Alitrunk with distinct promesonotal suture. Propodeum bluntly rounded where declivity meets base. Petiole erect, thickened anteroposteriorly, more convex anteriorly than posteriorly, superior border blunt and subtruncate. Mandibles, clypeus, occipital lobes, pronotum, prosternum, coxae, trochanters, flexor surfaces of legs, petiole and gaster with erect hairs. Pubescence on body fine, appressed, and sparse, but denser on appendages. (Identification from Smith, 1947).

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 occipital lobes, both of which are lacking in P. montivagus (1 or 2 erect hairs may b epresent on each of the occipital lobes 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. breviceps by having much longer scapes, scapes in P. breviceps are not as long as interocular distance; by not having the antennal scapes terminating in a club (scapes in P. breviceps 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, they immediately enter the colony and very quickly reappear from the colony carrying either a single pupa in a cocoon or a larva in each of 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]. 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.

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