Thomas G. Shelton, J. T. Vogt, and Arthur G. Appel

AAES researchers have found that a fascinating coexistence occurs in the insect world between two natural enemies. Field study results show that termites may be using the mounds of fire ants, one of the termite's major foes, as incubators to shorten their reproductive development.

Eastern and southeastern dark subterranean termites are native to the southeastern United States, including Alabama. They are some of the most economically important pests in the Southeast because they can seriously damage homes and other wooden structures. These termites form nests underground, and feed on wood at the soil surface. They regularly fly out of their nests (swarm) to start new colonies. These flights occur usually in the spring and fall, normally just after a rain when temperatures are above 80^oF and the wind is calm. Alates, the flying form of termites, are responsible for the formation of new colonies, and become the kings and queens of the new colonies. Termite colonies also include workers, which perform all the building and feeding of the colony, and soldiers, which defend the colony. Due to their subterranean habits, little is known about the interactions of these termites with other species.

Since termites are normally found in forested areas and fire ants are found in disturbed, open areas, their habitats overlap predominantly at forest edges. Researchers working with Alabama's Fire Ant Management Project had noticed the presence of termites in red imported fire ant mounds during earlier surveys. To learn more about this interesting coexistence, researchers conducted surveys of termite populations in fire ant mounds in 1997 and 1998 in Lee and Macon counties from early spring to early summer each year.

J.T. Vogt dissecting a fire ant mound.

Termites were found in approximately 25% of the mounds examined. In addition, the number of mounds infested with termites changed over time, ranging from 47% in May to only 11% in June (see figure). By June, native termites are past their spring flight season. Normally, most termites in a feeding area would be workers (about 90%), a few pre-alates (7-8%), and a very small number of soldiers (2-3%). However, the fire ant mounds contained mostly pre-alates (about 60%), rather than workers. This information suggests that the termites may be using the ant mounds for alate development.

Percentage of fire ant mounds containing termites during spring, 1997-98.

Why might termites inhabit dangerous fire ant mounds? Ant mounds sustain higher temperatures than the surrounding environment. The data indicate that the termites were not there to feed, but probably to take advantage of the ant mound environment. Termites, like all insects, have temperature-dependent development; therefore, higher temperatures mean faster development. Termite pre-alates may have been in the mounds to speed up their development. As the flight season came to a close in June, fewer mounds contained termites (see figure), since they form fewer alates after the flight season.

Termites with fire ants in mound.	Fire ant mound temperature sampling.

Temperatures in the ant mounds and surrounding wood debris indicated that there were other areas near the mounds with equivalent temperatures (about 86^oF). Above-ground portions of the mounds were drier than the soil surrounding the mound. However, moisture was not related to termite movement into ant mounds, because the termites were found in all areas of the mound, even those that were dry.

Scientific literature reports that some termites use clay soils, such as those making up the ant mounds, to build tunnels and nests. Since the nearby soil was loamy topsoil, soil type may have initially drawn the termites to the ant mounds. The termites were found inhabiting mound areas not in use by the ants. Chemical interactions between the termites and the ants may allow the termites to avoid the ant-infested areas of the mounds.