Distribution: widespread throughout Britain except for Ireland and some offshore islands. Also across most European countries and central Asia.
Habitat: usually lives near rivers, streams, lakes, ponds and marshes. Sometimes away from water, even on dry downland.
Description: short, glossy hair and silvery- white underparts. Eyebrows and ear-tips often white.
Size: length, 14cm of which tail is just under half.
Life-span: 14-19 months.
Food: worms, insect larvae, snails, crustaceans, spiders, fish, frogs and tadpoles.
The water shrew is the largest of the five species of British shrews and like all shrews leads a hectic life, busy by day and night on the look-out for food. A shrew is very small, so it quickly burns up its energy reserves. If it did not feed continuously, a shrew would die within a few hours.
The water shrew usually lives alone and each one occupies a territory which it fiercely defends from other shrews. Fighting is common and shrill squeals can sometimes be heard as a territorial dispute takes place. Each shrew digs a shallow burrow system, sometimes in a bank with a tunnel leading to a nest chamber, which is lined with a ball of grass, roots and moss. The burrow system may have an underwater entrance.
Although the water shrew, as its name implies, tends to be found in watery habitats - it particularly likes watercress beds - it often lives away from water. Some live on stony beaches, probably feeding on sandhoppers and flies along the high tide line. Others may be found in farmland, woods and hedgerows.
Feeding and swimming
The water shrew alternates between short periods of activity and rest, making regular short trips out of its home to forage for food, poking its sensitive nose into every nook and crannie, pouncing on earthworms and any small minibeasts.
In the water, it has to paddle fast because air trapped under its fur makes it buoyant and if it stopped swimming it would bob up to the surface. A fringe of bristly hairs along the underside of the tail acts as a rudder and the tail can be used to grip twigs and branches. It hunts along the bottom of a river or stream, turning over stones with its grasping feet, and can stay underwater for 20 seconds at a time. Prey is carried ashore to be eaten.
The shrew's mouth is full of sharp, pointed teeth which allow it to hang on to prey securely as it chews. The saliva contains a poison which probably stuns larger prey, such as frogs, to stop them struggling. Sometimes a shrew hoards food when there is a plentiful supply. It eats roughly its own body weight in food each day.
The water shrew does not like being in the water for long and comes ashore often to dry itself. It squeezes along the narrow passageways of its tunnel to get rid of the water from its fur and then grooms itself thoroughly.
The height of the breeding season is in late May and June, although it varies with the weather. Shrews communicate with each other by scent and high-pitched squeaks and twitters. The male approaches a female to see if she is ready to mate. If she is not they may fight instead.
After a gestation period (time between mating and birth) of 24 days, 3-8 young are born in a chamber within the female's burrow. The new-born babies are blind and hairless. At about 4 weeks old they venture out of the nest and the family often travels in procession, the mother leading and the babies hanging on to the one in front. At five weeks they are full size and their mother drives them away. By this time the female may already be pregnant again. The young from an early litter may breed that same year. Many youngsters die during the winter, killed either by cold, starvation or predators.
Water shrews and humans
The water shrew is the least abundant and least widespread of the British shrews but it is not considered rare. In some areas it seems to have declined drastically in numbers and this is probably due to the destruction of its habitat by the draining of waterways and wetlands and pollution.
Sometimes the water shrew is regarded as a pest because it eats the spawn of valuable fish stocks. Normally though, the shy, secretive water shrew is rarely seen and it is difficult to spot. If you are walking quietly along the bank of a slow-moving, clear, shallow stream, or in a watercress field, you may hear its shrill squeaks amongst the vegetation. Look carefully in the mud along a river bank for the shrew’s tiny footprints.
Image: Shrew (Water) by Wildlife in a Dorset garden
Information sourced from:
The IUCN Red List of Threatened Species (2015), Neomys fodiens [online], Available from: http://www.iucnredlist.org/details/29658/0 [accessed 13/09/2015].