Smittium (Harpellales, Legeriomycetaceae) belongs to a cosmopolitan group of filamentous fungi (Trichomycetes, Zygomycota) that live as obligate commensals in the digestive tract of various marine, freshwater, and terrestrial arthropods. The outcome of the paired introductions of three species of Smittium was investigated within the individual hosts of the mosquito Aedes aegypti (Culicidae: Diptera). In the first set of experiments, the host was inoculated with a single species of Smittium to determine whether hyphae location within the host was species specific. In the second experiment the host was exposed to two species of Smittium to determine whether hyphae showed positional displacement when two species of fungi co-inhabited the same host gut. Single species introductions of Smittium resulted in 80-85% of hosts with hyphae present only in the rectum. In all three paired combinations of Smittium species examined, only 40-65% of host larvae had hyphae restricted to the rectum. This is first study to experimentally demonstrate that the microdistribution of Harpellaceae hyphae can be influenced by the presence of a second species of Harpellaceae, suggesting a competition of the symbionts within the host.