Distribution, Spread, Activity Patterns, and Foraging Behaviors of the Introduced Ant Pheidole Obscurithorax in the Southeastern United States

A field survey of the southeastern United States showed that Pheidole obscurithorax Naves, an ant introduced from South America, inhabits a 50-mile-wide band along the coast between Mobile, Alabama, and Tallahassee, Florida, and is continuing to increase its range. Evidence suggests that P. obscurithorax has spread mostly by diffusion by natural means. It coexists with the fire ant Solenopsis invicta Buren, appears to be part of a largely exotic community of ants that are tolerant of highly disturbed habitats, and seems to have little negative effect on the ant communities that it invades. In Tallahassee P. obscurithorax is rapidly spreading, and its nest density increased by a factor of 6.4 over a two-year period. P. obscurithorax summer activity patterns appear to be regulated by time of day rather than by temperature, but they do not appear to be active above ground at temperatures over 36°C. Evidence suggests that foragers and nest-surface tenders are two separate populations and their activity is shifted in time relative to each other. The group prey retrieval tactics of P. obscurithorax related to prey size and mobility do not conform to predictions of central place foraging theory.