The Water Shrew (Neomys fodiens)





Recognition: The largest of the British shrews with a long pointed snout, small ears and tiny eyes. Fur is short, dense, velvety and jet black on the upper surface of the body, usually greyish white or yellowish underneath. Most have a tuft of white hairs on the ears and white hairs around the eyes. Stiff white hairs on the margins of the feet and on the underside of the tail forming a keel are very distinctive. The teeth are red-tipped. Head/body length: 67-96mm, tail 45-77mm Weight: 12-18g Lifespan: Water shrews are annuals with short lives lasting no more than about 19 months:

Diet: Their main food source is freshwater shrimps, water slaters 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.


The water shrew is found throughout mainland Britain but is probably rather local in northern Scotland. It is present on many of our larger islands, including the Isle of Wight, Anglesey, Arran, Skye and Mull but is absent from Ireland, the Scillies and the Channel Islands. It is semi-aquatic and is most often found in habitats close to water, including the banks of streams, rivers, ponds and drainage ditches, as well as reed-beds and fens. It is particularly numerous at water-cress beds. Occasionally it is found far from water in rough grasslands, scrub, woodlands and hedgerows; usually as young ones are dispersing. Although water shrews are widespread in mainland Britain, they have a rather localised occurrence, probably because of their preference for clean, clear sources of freshwater for foraging. They have low populations densities compared with most small mammals, with a maximum of about 9 shrews per hectare in favoured sites such as water-cress beds. Water shrews inhabit burrows and come out to feed on invertebrates.  The water shrew is most unusual amongst mammals in possessing venomous saliva. A mild toxin secreted into the saliva in the mouth helps to stun the prey. Even humans can feel the effects of this if bitten by a water shrew. 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. They do not hibernate; they remain active all through the year, diving for aquatic prey even in mid-winter. The fur is denser than in other shrews, efficiently insulating them against cold and wet. They groom frequently by scratching and licking which helps keep it in good condition and prevent water-logging. 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. They breed throughout the summer, producing two to three litters, each with 3-15 young, between April and September. Females produce their young in a nest woven from dry grass, usually in a burrow or under a log. After breeding the adultís 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. The main predators of water shrews are tawny owls and barn owls, but kestrels, foxes and even predatory fish such as pike occasionally catch and eat them. However, they only form a small proportion of the diets of all these predators. Some predators, including domestic cats, will catch and kill shrews but not eat them because they are rather foul-smelling. Shrews possess scent glands which are an important part of their social life, used in marking out territories. These scent-glands produce strong-smelling oily substances which many predators, including cats, find very distasteful. Water shrews harbour a great variety of parasites, including fleas, ticks and mites amongst the fur, and tapeworms and flukes in the alimentary canal. The large number of internal parasites is the result of shrews eating invertebrates, particularly snails, which act as the intermediate hosts of the parasites.


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 probable reasons for any decline in their numbers are habitat loss and 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. In common with other shrew species, water shrews are protected under Schedule 6 of the Wildlife and Countryside Act (1981). This permits shrews to be captured only by those in possession of a licence. Precautions are required to minimise the possibility of death through cold and starvation faced by any shrews captured incidentally while trapping for other small mammals: these include providing adequate bedding and food in the traps. Information on trapping and the law is given in Live Trapping Small Mammals, a practical guide available from the Mammal Society.



Carter, P. Birt M & Churchfield, S. (2006) Distribution and habitat occurrence of water shrews in Great Britain. Environment Agency, Almonsbury, Bristol. Carter, P. & Churchfield, S. (2006). The Water Shrew Handbook. The Mammal Society. Churchfield, S. (1988) Shrews of the British Isles. Shire Natural History Series No. 30. Shire Publications. Gurnell, J. & Flowerdew, J.R. (1994) Live Trapping Small Mammals A Practical Guide (3rd edn.) The Mammal Society, London. Harris, S. & Yalden, D.W. (2008) Mammals of the British Isles,: Handbook, 4th edn.). The Mammal Society, Southampton.