By Charlotte Owen
There are three types of shrew in Britain and their names are satisfyingly straightforward: the pygmy shrew is the smallest, the common shrew is the most numerous, and the water shrew is the best swimmer. It is also the largest, with a body length of about 15 cm including the tail, and quite possibly the feistiest. This is a trait that all shrews are renowned for, and they will frequently engage in fierce territorial battles over hunting grounds, but the water shrew takes things one step further: it is our only venomous mammal, using its toxic saliva to immobilise frogs, newts and even small fish.
Enjoying the best of both worlds, they are equally efficient on land and in the water, and almost constantly busy in their search for sufficient food to fuel their fast metabolism. Typical habitats include ponds, streams and reedbeds but water shrews have also been recorded in damp woodland, hedgerows, heathland and even vegetated shingle.
Alongside the typically shrew-like features of tiny eyes and an elongated nose, water shrews have some specialist adaptations to suit their semi-aquatic lifestyle. Their feet have a fringe of stiff, silvery bristles to help them paddle and their tail has a hairy ‘keel’ on the underside for extra propulsion - and they do power furiously through the water, moving like a manic bath toy wound up to top speed.
Their dense fur traps thousands of tiny air bubbles, giving them a silvery appearance underwater and providing vital insulation, but the bubbles also increase buoyancy. This means a water shrew can only stay submerged for a few seconds; just enough time to grab a freshwater shrimp, snail or caddis larva before swimming back to the surface to eat it. As a result they tend to prefer shallow water but will dive to depths of a metre or more in search of an aquatic snack amongst stones and submerged plants. After a particularly deep dive, they may emerge looking a bit bedraggled because their distinctively dark fur is water-repellent but not completely waterproof, so it takes a considerable amount of shaking, grooming and scratching to dry off after a dip.