Water shrews are the largest of the three British mainland shrews. They can be up to 96 mm long, with a tail of another 77 mm and they can weigh up to 18 g. They have the shrew’s characteristic long pointed snout, small ears and tiny eyes. The adult fur is short, dense and black on the upper surface, withbuff-grey chin, neck and underbelly, usually with tufts of white hairs on the ears and around the eyes. Males and females are alike. Juveniles are dark all over and, rarely, adults remain entirely black. Looking closely, you can see that there are stiff hairs on the margins of the feet, and along the underside of the tail forming a keel, an adaptation for aquatic activity. Water shrew fur is denser than that of other shrews, being suited for their aquatic lifestyle. They groom their coat frequently to maintain its condition and prevent water-logging. The water shrew is the only small British mammal likely to be seen swimming under water, although moles are excellent swimmers when necessary. Water voles are much larger with blunt noses and short tails, and are currently thought to be absent from Cornwall.
Water shrew droppings are up to 10 mm long and black when wet, and pale grey when dry, and they may contain white fragments of aquatic crustaceans. They may be deposited on streamside rocks or at the entrance to burrows. The burrows are made in the banks of streams and rivers and are about 20 mm across. Unlike bank voles, water shrews do not disturb the vegetation around their burrow entrances.
© Jane Simpson
© Chris Robbins
Water shrews tend to be nomadic, ranging more widely than the common and pygmy
shrew. Population densities are relatively low, about 9 animals/hectare in good quality habitat. They are most likely to be found in clean, freshwater habitats, typically along the banks of waterways including drainage ditches. They also frequent ponds and reed beds. Watercress beds are particularly favoured for the quality of the water. Animals disperse after the breeding season and may turn up far from water, in grassland, scrub, hedgerows and even urban gardens. Water shrews feed on a wide variety of aquatic and terrestrial invertebrates, depending on season and availability in the habitat. Their impressive carnivorous dentition makes short work of prey such as beetles, woodlice, earthworms and snails, as well as freshwater shrimps, water slaters and caddis larvae, for which the animals dive to a metre or more. Larger prey such as small frogs, newts and fish may be taken. A mild venom secreted in the saliva helps to overcome prey. The venom can cause a reaction in humans.
Water shrews are generally solitary, and territorial. However, they are more tolerant
of others living nearby if the habitat is of sufficiently high quality. They lead a short,
highly energetic life of about 19 months and do not hibernate. Their constant need for
food requires them to remain active all year. The adults produce two to three litters
of 3 to 15 young between April and September. A nest of dry grassy material is
constructed by the female in a burrow or similar cavity. After breeding the adults die.
The juveniles that survive the winter become sexually mature in the spring.
The main predators of water shrews are barn and tawny owls, and occasionally other
raptors. They may also be taken by opportunist predators such as foxes or even pike.
However, shrews possess scent glands for territorial marking, producing strongsmelling
oily substances, which some predators, such as cats, find distasteful. The loss and degradation of their habitat is probably the most significant threat to water shrews.
Small mammal trapping. Plastic bait tubes. Incidental sightings.
Cat kills and
incidental records. Corrugated iron sheets.
Water shrews in one north Cornish garden have set up home in the garden pond and are often seen checking out the bird table. Dead shrews of all species are often found on open ground and a dead water shrew was found in Laneast village, near Launceston, several hundred yards from the nearest stream or pond.
Water shrews are widely distributed across Cornwall, generally close to water courses and ponds. They are probably under-recorded due to the lack of targeted surveys. They occur throughout England, Wales and southern Scotland. Water shrews are not found in Ireland. They are found across Europe and into Asia.
Did you know?:
Water shrews and other shrews are very vocal and communicate mainly in the ultrasonic range. They may be able to echolocate around their environment and bat detectors can be used to record their vocalizations but there is no distinctive call pattern between different species of shrews that would help identify them.
Water shrews are never very abundant and it is difficult to detect population changes. Declining numbers may result from habitat loss and reduction in habitat quality through pollution or physical destruction. Water shrews are protected under Schedule 6 of the Wildlife and Countryside Act 1981. They may only be captured by those in possession of a licence issued by Natural England. Because of their constant need to feed, all shrews risk death by starvation when trapped. Traps must be provided with adequate bedding and food, and checked frequently..