Water shrews are the largest of the British shrews. These frantic little mammals are very well adapted to an aquatic lifestyle. They have a dark black-brown coat of short fur that is paler underneath and which is waterproof and stays dry, even while swimming. Unlike the other shrews found in Britain, they have hidden ears, only visible as white tufts, which they can close when they are in the water. They have a stiff fringe of hair beneath their tail, which they use as a rudder when swimming and they can dive to depths of over 70cm.
Water shrews are mostly active at night, particularly just before dawn. They need to eat 50% of their body weight every day to stay alive and can travel up to 160 metres along the water’s edge to find food and shelter. They do not hibernate but remain active throughout the winter when their dense fur protects them from the cold and wet.
Pregnancy lasts roughly 20 days and 3-5 young are born per litter between April and September, with a peak of activity in May and June. Females have between one and three litters in a season. The juveniles usually leave the nest at six weeks old.
Mainly freshwater crustaceans such as shrimps, caddis-fly larvae and small snails, but also small fish and frogs, earthworms, snails and beetles.
Usually unpolluted, fast flowing water, in reed-beds, watercress beds, fens and along riverbanks. They dig extensive networks of small burrows and chambers, about 2cm wide, in the banks of streams, which they line with grass and leaves.
Predators & threats
Occasionally owls, kestrels, foxes, large fish and cats but most water shrews die from exhaustion after the breeding season.
Status & distribution
Water shrews are widely distributed throughout mainland Britain, but generally uncommon. They are scarce in the Scottish highlands and absent from Ireland and most of the small islands.