Status of the Harvester Ant (Pogonomyrmex spp.; Hymenoptera: Formicidae) Fauna of Arkansas

Abstract

Pogonomyrmex Mayr (Hymenoptera: Formicidae) species are collectively termed harvester ants due to their well-described habit of collecting seeds for food (Cole, 1968). North of Mexico, the genus is most speciose in western and southwestern portions of the United States (Johnson, 2000b). Harvester ants are generally associated with xeric, open natural community types such as deserts, grasslands, and woodlands (Taber, 1998). Nests are constructed in soil and characterized by craters or small to large mounds of soil. Some harvester ant species actively clear vegetation from a roughly circular area surrounding nest mounds (Cole, 1968) making these sites conspicuous landscape elements. Once established, a harvester ant colony can persist for decades (MacMahon et al., 2000). Warren and Rouse (1969) list three Pogonomyrmex species as occurring in Arkansas, P. badius (Latreille), P. barbatus (Smith), and P. comanche Wheeler. Their records were gleaned from, what is today, the University of Arkansas Arthropod Museum (UAAM). In an attempt to reassess the status of the genus in Arkansas, I visited the UAAM to examine their Pogonomyrmex holdings and also conducted field surveys for harvester ant colonies in remnant natural communities across the state from 2007–2009. Survey methodology consisted of visually searching sites for foraging workers and nest mounds or craters. A total of 32 sites, in or near counties with occurrence records of harvester ants, were surveyed across Arkansas. Sites surveyed comprised a number of different natural community types including blackland prairie, saline barrens, sandhill woodlands, and tallgrass prairie. The record of P. badius in Arkansas is interesting as this the only Pogonomyrmex species known to occur primarily east of the Mississippi River (Cole, 1968). Its distribution is centered on the Coastal Plain of the southeastern United States and is generally described as ranging from North Carolina, south to Florida, and west to Louisiana (Johnson, 2000b). Warren and Rouse’s (1969) records for P. badius are from Logan and Scott Counties in west-central Arkansas far from the species main range. The authors hypothesized the species potential occurrence ‘‘in the grassland extension of the Oklahoma prairie into western Arkansas.’’ However, neither county cited as hosting P. badius contains the soil types that would support the species colonies. Pogonomyrmex badius colonies are associated with open, xeric natural communities (sand barrens, sandy ridges along streams) on deep, well-drained sandy soils (Cole, 1968; MacGown et al., 2008). Most of Logan County, and a portion of Scott County, are situated in the Arkansas Valley Plains and Scattered High Ridges and Mountains of the Arkansas Valley (Woods et al., 2004). Prior to European settlement, these areas were typified by oak-hickory-pine forests, savannas, and tallgrass prairies. The remainder of Scott County lies in the Fourche Mountains dominated by extensive oak-hickory-pine forests. Both counties are devoid of the deep sand habitats preferred by P. badius. Given these facts, the occurrence of P. badius in Arkansas seemed questionable. My visit to the UAAM supported the notion that Warren and Rouse’s (1969) records for Arkansas were dubious as the specimens once attributed to P. badius have since been re-determined to be workers of P. barbatus. Until contradictory evidence is presented, the presence of P. badius in Arkansas should be considered as tentative. Pogonomyrmex barbatus is a harvester ant that would be expected in Arkansas given its habitat affinities (McCook, 1880; Taber, 1998) and presence in Oklahoma and Texas (Johnson, 2000b). Warren and Rouse (1969) list the species as occurring in Bradley, Crawford, Scott, and Washington Counties. Logan County can now be added to that list given information presented herein. The UAAM also contained specimen records of P. barbatus from Van Buren County not previously noted by Warren and Rouse (1969). Crawford, Logan, Scott, Van Buren and Washington Counties are all along or very near Arkansas’s western border. Bradley County is located in south-central Arkansas. Unlike P. badius, P. barbatus colonies are associated with more mesic areas, especially those sites with higher clay content in their soils (Taber, 1998; Johnson, 2000a).