Some field observations on the pilid Pomacea haustrum (Reeve, 1856), predator-competitor of schistosomiasis mansoni planorbid intermediate hosts have shown that: Copula and oviposition are preferably carried out at night or at dawn. Eggmasses - whose dimension and shape depend on the number of eggs and types of supports - are often laid from 6 to 10 com above the water level and hatched 9 to 30 days after incubation; the average number of eggs/egg-mass was 236. Habitual food consist of confervoid algae, besides natant and submerged aquatic vegetation; it is common, however, the utilization of the other material as food. Its habitat is the shallower marginal zone of hidric collections, predominatly in lentic surrounding. Its spacial distribution is conditioned to the biotipe special characteristics. Some aquatic birds - anatid, ralid, etc. - reveal important natural enemies, attacking both young and adult specimens, besides the egg-masses; under certain conditions they may be an impedictive factor to the establishment and colonization of this pilid in new biotopes.