Composition of parasite communities can vary across host individuals, populations, species and communities (Carney & Dick, 2000; Poulin & Valtonen, 2002; Calvete et al., 2004; see Chapter 16). The source of this variation is the diversity of the hosts' biotic and abiotic environment. For example, a richer community of co-habitating hosts increases the probability of lateral transfer of parasites, and thus affects the species richness and composition of the xenocommunity (Caro et al., 1997). The abiotic environment external to a host, such as air temperature or substrate, can also affect parasite species composition (Galaktionov, 1996). Therefore, some part of a parasite community encountered in a host is due to its specific location, another part due to host identity, and yet another part due to the host's environment (Kennedy & Bush, 1994). However, the relative importance of spatially variable factors in variation of community composition is poorly known for most parasite and host taxa. Moreover, most studies of spatial variation in parasite communities have been done on helminth communities (e.g. Bush & Holmes, 1986; Carney & Dick, 2000; Calvete et al., 2004). Therefore, it is not surprising that the hypothesis that host identity is a major determinant of parasite community structure has been supported (Bell & Burt, 1991; Buchman, 1991; Guégan et al., 1992). One of the reasons for this can be the relative stability of the internal environment of a host organism (Sukhdeo, 1997).