Field investigations on 12 populations of Omphiscola glabra were carried out in central France over a 5-year period to determine the ability of the species to aestivate in its habitats when summer drying occurred. In the department of Haute-Vienne, spring-born snails aestivated with their apertures applied to the surface of a substratum and most of them were located on the banks of ditches. With the return of wet conditions, the survival of these snails was low. In the department of Indre, most springborn snails aestivated by burrowing into the marl and were distributed over the whole surface area of their habitats. Higher survivals were noted for these O. glabra after aestivation. Despite a significant difference in the frequencies of buried lymnaeids, the position of snails with a natural infection with F. hepatica in their dried habitats was similar to that found for uninfected ones. The variations found in the aestivation of O. glabra might be explained by the dominant substratum (granite gravel and scarce mud in Haute-Vienne, or a thick layer of marl in Indre) and the plant cover on ditch bottoms.

Malacological investigations were carried out in 53 meadows on acid soil to identify the characteristics of habitats colonizedby lymnaeid snails. These meadows are located in three different geographical districts (Basse-Marche, Monts d'Ambazac, Plateauxde la Vienne) in the Haute-Vienne Department (central France). Lymnaea truncatula lived at the distal extremity of opendrainage furrows ; L. glabra inhabited the middle part of furrows and L. palustris lived in the central ditch. The mean area of L.truncatula habitats ranged from 2.8 to 4.8 m2 in relation to the district studied and was smaller than those of L. glabra (a meanof 3.6 to 7.2 m2 ) and L. palustris (10.3 to 19.3 m2). Mean intervals between the sites occupied by L. truncatula and L. glabraranged from 6.3 to 12.3 m ; they were greater between the sites occupied by L. glabra and L. palustris (11.6 to 15.4 m). Finally,the mean densities of L. truncatula in June ranged from 11.4 to 19.8/m2 in relation to the district studied ; those of L. glabra rangedfrom 22.6 to 27.0 snails/m2, whereas in L. palustris, they ranged from 6.3 to 8.8 snails/m2. The mean values of these first twoparameters were significantly lower in the habitats located in Monts d'Ambazac than those recorded in the two other districts. Implicationsof these results for fasciolosis control are discussed.