Water Shrews – Neomys fodiens
Protected in the UK under the Wildlife and Countryside Act, 1981.
Water shrews are the largest British shrew. They are busy little mammals who are well adapted to an aquatic lifestyle. They have a dark black-grey coat of short fur that has a white underside and which is waterproof. They have hidden ears, only visible as white tufts, which are closed 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. Although they don’t have webbed feet, they have large hind feet with a row of stiff hairs and are the only shrew likely to be seen in the water.
Water shrew; dense fur and hidden ears.
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. Water shrews 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 3-15 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. Water shrews are generally solitary, each maintaining its own territory, although they frequently live in close proximity to each other in a favoured area of stream-bank. Females produce their young in a nest woven from dry grass, usually in a burrow or under a log. After breeding the adults die-off and the young shrews carry the population through the winter before becoming sexually mature the following spring, ready to breed in the summer following their birth.
Water shrew, they can leap out of the water to catch prey in the air.
They spend their time hunting for invertebrate prey, even swimming underwater to catch caddisfly and mayfly larvae. Their main food source is freshwater shrimps, small snails, water skaters and caddis larvae which they obtain by diving and hunting underwater. Occasionally frogs, newts and small fish are eaten. They also feed on many terrestrial invertebrates such as earthworms, snails and beetles.
Occasionally water shrews are killed by birds of prey, foxes, large fish and cats but most water shrews die from exhaustion after the breeding season.
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 including for the Channel Islands, the Isles of Scilly, Scottish islands and the Isle of Man. They are found on some of our larger islands, including the Isle of Wight, Anglesey, Arran, Skye and Mull. Occasionally the species is found far from water in rough grasslands, scrub, woodlands and hedgerows, usually as young are dispersing. They have low populations densities compared with most small mammals.
Unlike other shrew species found in Britain, the water shrew has venomous saliva that stuns its prey. Over the centuries, this has led to many myths surrounding them. In Ancient Egypt, they were worshipped and mummified, whilst the Greeks and Romans believed that these little creatures were a source of evil! Even though the shrew’s bite rarely punctures the skin, a red rash appears at the site of the bite which is sore to touch for several days. Water shrews have red tipped teeth, caused by iron pigment deposits; this wears away with time.
Because water shrews are never very abundant, it is difficult to tell if their populations are under threat. They are still numerous in many sites where long-term studies have been conducted. The likely reasons for any decline in their numbers are habitat loss and water pollution. While they can tolerate a good deal of disturbance from human activities, drainage schemes and river-bank clearance may adversely affect them by altering the water supply, reducing their food supplies, destroying their burrows and the vegetation cover. They are very vulnerable to pollutants and pesticides in the water which they ingest indirectly via their prey and directly through their grooming activities.
Thanks to Lev Dahl at Wiltshire Wildlife Trust who inspired this article.