Rarely found far from water, the water shrew is extremely well adapted to its aquatic lifestyle (7). Although the eyes of the water shrew are small and vision is poor, it has acute hearing and an excellent sense of smell. In addition, the hairs on the feet trap air, allowing the water shrew to run across the surface of water (2) (5) (8).
The water shrew regularly dives under the water to capture prey or to avoid danger, sometimes remaining below the surface for over 30 seconds at a time (7). During dives, air bubbles trapped in the fur reduces heat loss, although the bubbles also make the water shrew fairly buoyant, meaning that it must paddle vigorously in a walking motion to propel itself forwards (5) (7) (10).
Mostly active during the day, the water shrew consumes a large amount of food given its small size (1) (8). Due to its high energetic demands, the water shrew can only survive for about three hours without food (5). Aquatic insects form the bulk of the water shrew’s diet (1) (5) (10). Slugs, snails, earthworms, small fish, amphibians and spiders may also be taken (2) (7), and the water shrew may occasionally feed on terrestrial invertebrates such as grasshoppers and crickets (2) (5) (10).
The water shrew forages using its sensitive nose, which has specialised hairs or whiskers, called ‘vibrissae’. During times when prey is abundant, the water shrew may cache food in hollow logs or crevices, returning when food is scarce (2) (5) (7).
Breeding occurs from February to August in North America (1). The nest is typically made from grass and plant material, with a depression in the centre (8), and is placed close to water, usually in an underground burrow, on a raft of logs or in a beaver lodge (1). The water shrew may also construct tunnel systems, or it may use those of other species (7) (8).
The water shrew may have up to three litters a year, each with between three and ten young (1). The gestation period lasts for around three weeks and, following birth, the young water shrews develop rapidly. The water shrew does not reproduce until after the first full winter, and it has a short lifespan, usually only living to about 18 months (1) (2) (5).