Technical Abstract: Red imported fire ants (RIFA); Solenopsis invicta, currently infest over 275,000,000 acres in 11 states and Puerto Rico. A congener species, S. richteri, inhabits a relatively small area in northwestern Alabama, northeastern Mississippi, and southern Tennessee. Interbreeding between S. invicta and S. richteri results in the production of a fertile hybrid form. Range expansion continues primarily by S. invicta and the hybrid form, by both natural and artificial means. Recent isolated infestations in Phoenix, AZ (Collins unpublished), Virginia (Waller 1993), and Tennessee (Milam unpublished), suggest that fire ants are becoming acclimated to harsh environments and continued range expansion may result. Some scientists have speculated that hybrid vigor may enable the hybrid to survive in colder areas than the parental forms. In December 1992, an isolated 3,000 acre infestation was discovered near the town of Calhoun, TN approximately 45 miles northeast of Chattanooga, TN. A wood pulp processing plant appeared to be the source of the infestation. The original infestation may have been introduced onto the plant site on construction equipment or material. This population appears to be well adapted and thriving. To learn more about this isolated population, several ecological studies were initiated in 1993. We report here preliminary data. The final results of these studies may offer better estimates of the ultimate range of imported fire ants.