A large number of planorbid snails are now commonly transported by man mainly
through the aquatic plant trade. However, only a restricted number of species
establish viable populations in a new habitat and a more restricted number
spread. Only five planorbid species can be ranked in this last category and can
be considered as pests because of their role in the transmission of parasites to
humans or domestic animals: Biomphalaria glabrata, B.
straminea, B. tenagophila, B.
pfeifferi and Indoplanorbis exustus. The
neotropical B. glabrata, B. straminea and
B. tenagophila have proven their capacity to invade another
continent sometimes creating new transmission foci. The African B.
pfeifferi and the Indian I. exustus have also
expanded their distribution area with long-distance dispersal. Other planorbid
species, i.e. Helisoma duryi, Amerianna carinata and
Gyraulus spp. have been able to establish viable
populations, but not to spread, presumably because they are limited to specific
habitats or/and display poor competitive abilities.