Though the brown rot fungus Gloeophyllum trabeum Pers. ex Fr. is attractive and beneficial to most subterranean termites including Coptotermes formosanus Shiraki, we found that Formosan subterranean termites suppress the growth of this fungus. Fungi were isolated from the external surface of Formosan termites. Dual culture tests of selected fungi against G. trabeum showed that these fungi were antagonists and effectively controlled the growth of G. trabeum. Identification, mode of dispersal, and prevalence of these parasitic fungi from field collected colonies are being researched to determine the strength of this symbiosis.