The water shrew is one of Britain's least known mammals. It is the largest of the native shrews, extremely fierce and territorial.
Water shrews are up to 10cm in length with a 4 - 7cm tail. They have short, glossy fur, black on the back and silvery grey on the underside. They have a long pointed snout, small ears, tiny eyes and red-tipped teeth. They have very distinctive stiff white hair on the margins of the feet and underside of the tail, forming a keel.
The layer of bubbles trapped in their dense fur means that water shrews often appear silvery when diving. The bubbles also make them buoyant so they can only remain submerged for a few seconds. Water shrews often anchor themselves to rocks or plant stems to remain under water.
Shrews are very small and use their energy reserves quickly. They live a hectic life, awake and feeding continually both day and night, all year round. Water shrews consume approximately half their own bodyweight in food each day.
Water shrews eat mainly freshwater shrimps, water slaters and caddis larvae from the water, and terrestrial invertebrates such as earthworms, snails and beetles. They will also eat prey considerably larger than themselves, for example frogs, newts and small fish.
Water shrews are unusual amongst mammals because they have poisonous saliva which helps to stun the prey. In the unlikely event of a water shrew biting a human, the bite will rarely puncture the skin but will still result in a red and painful rash, lasting several days.
Water shrews are widespread throughout Britain, though not in Ireland or some offshore islands. They are found across Europe and central Asia. They prefer clear, fast-flowing, unpolluted rivers and streams but also live near ponds and drainage ditches. They especially favour watercress beds. Despite their name, water shrews may live in woods, hedgerows and farmland away from water.
Finding water shrews is difficult as they tend to remain hidden in burrows and amongst vegetation. They are more easily heard than seen, making high-pitched squeals and a "churr churr" sound, especially during the summer breeding season.
There is a lack of knowledge about the water shrew population and large gaps in its distribution records. The draining of waterways and wetland pollution may be causing a decline in numbers. The Cambridge Greenbelt Project is conducting a water shrew survey, as part of a national survey organised by The Mammal Society. The survey is gathering information and providing baseline data. We are looking for volunteers to learn about water shrews and undertake surveys. If you would like to be involved please contact us for details.
Find out about what's been seen on our sightings page, or take a look at details of some of the projects and sites that we work on.