Water Shrew: Ecology and Welfare
The water shrew (Neomys fodiens) is Britain's largest shrew and one of its most specialised small mammals — adapted for life at the water's edge with dense waterproof fur, fringed feet, and a venomous bite. Its welfare and survival are tightly linked to water quality and riparian habitat.
Ecology and Adaptations
Water shrews are semi-aquatic, hunting invertebrates, small fish, amphibians, and crustaceans in and around clean streams, rivers, and pond margins. Their dense fur traps air bubbles providing buoyancy, and specialised fringe hairs on feet and tail improve swimming efficiency. Unusually for a mammal, they possess venomous saliva — effective for subduing larger prey items.
Their extreme metabolic rate (shrews must eat approximately their body weight daily to avoid starvation) means they are highly vulnerable to short periods of food unavailability. Energy reserves are exhausted within hours — food deprivation, injury, or cold water that reduces prey activity can cause rapid starvation.
Habitat Requirements
Clean, well-oxygenated water with abundant invertebrate prey, dense bankside vegetation providing cover and nest sites, and undisturbed bank profiles supporting tunnel burrows are essential requirements. Agricultural run-off reducing water quality and invertebrate abundance, channelisation of watercourses, and removal of bankside vegetation directly reduce water shrew populations.
Water shrews are indicators of water quality — their presence signals a healthy, invertebrate-rich aquatic system. Their decline or absence indicates environmental degradation.
Welfare Challenges
Water shrews are occasionally caught in conventional mammal live traps — the Longworth small mammal trap is used for survey work. Their metabolic rate requires that traps be checked at least twice daily, with adequate food provided (worms, blowfly pupae) in the trap to prevent starvation of captured animals. Trap checks in hot or cold weather require increased frequency.
Cat predation affects water shrews in riparian habitats adjacent to human habitation. Cat-worn bells have limited effectiveness for highly mobile prey species like shrews. Keeping cats indoors during dawn and dusk reduces predation.