Biological invasions: the case of planorbid snails

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. pfeifferiandIndoplanorbis exustus. The neotropicalB. glabrata,B. stramineaandB. tenagophilahave proven their capacity to invade another continent sometimes creating new transmission foci. The AfricanB. pfeifferiand the IndianI. exustushave also expanded their distribution area with long-distance dispersal. Other planorbid species, i.e.Helisoma duryi, Amerianna carinataandGyraulusspp. 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.