Sheep have been grazing wet areas, ditches, ponds

High summer rainfall is required for the fluke life cycle to take place and for the mud snails, which act as intermediate hosts, to rapidly increase, leading to a build-up of infective fluke stages as the summer progresses.  Mud snails prefers wet mud to free water, and permanent habitats include the banks of ditches or streams, marshy areas and the edges of small ponds. Following heavy rainfall or flooding, temporary habitats may be provided by hoof marks, wheel ruts or rain ponds. Fields with clumps of rushes are often suspect sites.