Filariomyces forficulae occurs commonly on the earwig, Labidura riparia, in Florida. The hypopial stage of a mite, Histiostoma sp., often associated with L. riparia is also sometimes infected by the same fungus. Some other earwig species that occur with L. riparia were not found to be hosts. Sites of fungal infection on the earwig were highly variable and influenced by several factors. F. forficulae was transmitted by several types of insect contact including mating with varying efficiencies and by a mechanical inoculation technique. Developmental time required by the fungus from ascospore to mature perithecia was 10–12 days at 24°C. In laboratory studies there were small but consistent differences between longevities of infected and noninfected groups of earwigs and infected populations of earwigs died sooner than noninfected ones. Infection resulted in differences in pattern of egg production; however, no numerically significant differences in total egg production or egg-hatching ability between the two groups were found.