Les habitats des Lymnaeidae sur sols acides : A propos de quelques observations dans la région Limousin sur une trentaine d'années

As several lymnaeids such as Galba truncatula are natural intermediate hosts of a parasite: Fasciola hepatica, in the Limousin region, field investigations were carried out in 366 farms (a total area of 38,574 hectares) to identify the species of Lymnaeidae living on these acid soils, to determine the frequency of their habitats, and to find the type of habitats with the highest numbers of snails for each species. More than 60% of G. truncatula habitats (out of 7709) were located at the upstream extremity of open drainage furrows in swampy meadows. The highest numbers of G. truncatula were found in these sites. Most habitats of Omphiscola glabra (out of 3137) were located in the same open drainage furrows (42.8%) and in road ditches (28.2%). The most abundant populations of O. glabra were found in the former sites. More than 62% of Radix ovata habitats (out of 736) were smooth-flowing brooks. Radix peregra, Stagnicola fuscus, and S. palustris were scarcer in the areas prospected, the number of habitats being less than 80 for each species in the 366 farms prospected. Lymnaea stagnalis and Radix auricularia were only found in a few habitats. The high frequency of G. truncatula and O. glabra habitats can be explained by the fact that the numerous swampy meadows on acid soils constituted the best habitats for the development of local populations, despite a low dissolved calcium content in water. The scarcity of habitats or their absence for the other lymnaeid species may be related to the quality of aquatic vegetation and to its quantity which is less lush in water collections of the Limousin region than in those located on the nearby sedimentary soils.