| Summary: | Field investigations were carried out during three periods (from 1976 to 1997, in 2013–2014, and in 2020–2021) on 39 cattle-raising farms on acidic soils to track changes in the populations of two Lymnaeidae (<i>Galba truncatula</i> and <i>Omphiscola glabra</i>) and their infection with <i>Fasciola hepatica</i> and/or <i>Calicophoron daubneyi</i>. Compared to the survey between 1976 and 1997 on these farms, there was a significant decrease in the number of the two lymnaeid populations and the size of the <i>G. truncatula</i> populations in both 2013–2014 and 2020–2021. This decline was significantly faster in the last nine years than it was before 2013. The area of habitats colonized by <i>G. truncatula</i> showed no significant variation over the years, while that of habitats with <i>O. glabra</i> significantly decreased in the period covered by the three surveys. The prevalence of <i>F. hepatica</i> infection in snails significantly decreased over the years, while <i>C. daubneyi</i> infection increased over time in both lymnaeid species. These changes are due to the use of triclabendazole to treat fasciolosis in ruminants since the 1990s, and are probably a consequence of the successive heatwaves that have occurred since 2018 in the region.
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