Our objective is to evaluate the habitat preference of freshwater snails in relation to environmental factors and the presence of the competitor snail
Melanoides tuberculatus
. In the first phase, snails was collected at 12 sites. This sampling sites presented a degree of organic input. In the second phase 33 sampling sites were chosen, covering a variety of lotic and lentic environments. The snail species found at Guapimirim, state of Rio de Janeiro, displayed a marked habitat preference, specially in relation to the physical characteristics of each environment. Other limiting factors for snail distribution at the studied lotic environments were the water current velocity and the amount of organic matter, mainly to
Physa marmorata
,
M. tuberculatus, and
Biomphalaria tenagophila
. The absence of interactions between
M. tuberculatus, and another snails could be associated to the distinct spatial distribution of those species and the instability of habitats. This later factor may favor the coexistence of
M. tuberculatus with
B. glabrata by reduction of population density. In areas of schistosomiasis transmission some habitat modification may add to the instability of the environment, which would make room for the coexistence of
M. tuberculatus, and
Biomphalaria spp. In this way, some of the usual measures for the control of snail hosts would prevent the extinction of populations of
Biomphalaria spp. by
M. tuberculatus in particular habitats.
