A large, solitary shrew which uses its hind feet to swim underwater in search of aquatic insect larvae.

Meaning of scientific name
'Sorex': from Soric (Latin) 'shrew-mouse'. 'Palustris': from Paluster (Latin) 'marshy'

Life span
18 months.

Statistics
13-17cm long including a tail of 6-9cm.

Physical description
A relatively large shrew, with dark brown-black fur (grey on the belly) and a long tail which is dark above and pale underneath. The hind feet are large, and both hind and forefeet have a fringe of stiff hairs to help increase their surface area. As in all shrews, the snout is very long and mobile.

Distribution
Alaska and Canada south to the northern mountains of the USA.

Habitat
Northern forests around streams and damp areas.

Diet
Aquatic insect larvae and terrestrial invertebrates.

Behaviour
Water shrews feed every 10 minutes, although they can survive up to 3 hours without eating. They are solitary, and aggressive towards each other. They are active throughout the day - particularly at dawn and dusk, swimming to forage by paddling vigorously with their hind feet to overcome the buoyancy of the air trapped in their coats. When they surface they dry themselves. When foraging they continuously emit high-pitched sounds, possibly for echolocation.

Reproduction
Breeding occurs between December and September, during which time several litters may be raised. Gestation is about three weeks and the litter can be 3-10 naked and blind offspring. Development is fast, and the youngsters are ready to breed in the summer or autumn following their birth. Life expectancy, however, is low.

Conservation status
Not currently threatened.

Voice
High pitched squeaks and possible echolocation sounds.

History
The earliest shrew fossils date back to the Eocene, 45 million years ago in North America.