Large cockroaches, such as Periplaneta Americana, typically harbour in their hindgut two or more species of parasitic pinworm (Nematoda: Oxyurida). Our laboratory colony was infected with three, possibly four species. The mechanism(s) permitting the sympatry of these potentially competing species were investigated by: i) repeatedly sampling over time hosts of various size to determine the structure, if any, in the pinworm guild and ii) infecting uninfected hosts with known doses of infective eggs and monitoring population changes via daily host dissections. Results indicate that chemically-mediated intraspecific interference competition maintains pinworm populations at densities well below the apparent carrying capacity of the majority of hosts. The concomitant reduction of interspecific pressures thus permits the cohabitation of multiple pinworm species in what is essentially a single niche. This intraspecific population limitation is likely a response to pressures produced by the large size of the parasite in relation the hindgut of early instar hosts. / Science, Faculty of / Zoology, Department of / Graduate