Scientists have found that there is a relationship between the abundance of some species of molluscs

Scientists have found that there is a relationship between the abundance of some species of molluscs in pastures and clay diseases in cattle. Explain this dependence?

Cattle are susceptible to helminthic infestations, i.e. diseases caused by parasitic worms. They are predominantly affected by flatworms. Among them are representatives of the Fluke class, digenetic worms (for example, liver flukes). One of their intermediate hosts is a mollusk (for example, a pond snail), in which a certain stage of the worm’s life cycle passes. Then a larva with a tail emerges from the mollusk, which attaches to coastal vegetation. Cattle eat this herb and become infected by the fluke.