Entomopathogenic fungi were among the first pathogens noticed to affect imported fire ant populations in their native range in South America. When spores of these fungi contact the host cuticle, the fungus germinates, penetrates the insect body, and starts growing in the insect body. Typically, an infected insect will die within 3-5 days. After death of the host insect, the fungus grows throughout the cadavers and emerges through the cuticle. Infective spores develop on the mummified cadaver, and a new cycle of infection can occur when healthy ants come in contact with the spores.

Both Metarhizium anisopliae and Beauveria bassiana are known to infect fire ants both in wild populations and in laboratory experiments. Other fungal species also occur under certain conditions. An Aspergillus sp. isolate has been isolated from dying ants used in rearing of parasitic Phorid flies. Studies with this fungus will determine whether the attacking phorid flies can transmit this pathogen, and the conditions under which the transmission occurs. Other studies with fungal isolates will focus on the selection of potential agents to be used in biological control programs.