Songbirds apply ants to their feathers during anting behavior, possibly as a method of reducing feather parasites. We tested polar and nonpolar ant secretions and pure formic acid for bactericidal and fungicidal effects on microbial ectoparasites of feathers. Microbial inhibition trials were run with the bacteria Bacillus licheniformis (strains OWU 138B and OWU 1432B) and B. subtilis; and with the fungi Chaetomium globosum, Penicillium chrysogenum, and Trichoderma viride. Ant chemicals were derived from Camponotus pennsylvanicus, Pheidole dentata, Aphaenogaster rudis, Crematogaster lineolata, and Lasius flavus worker-caste ants. Although pure formic acid strongly inhibited all bacteria and fungal hyphae tested, concentrations of formic acid found in the bodies of formicine ants did not. Neither hexane ant-chemical extracts nor ant suspensions in deionized water inhibited the microbial species. Consequently, the hypothesis that birds apply ants to control feather parasites was not supported.