Perhaps because they never featured in the children's bookThe Wind in the Willows, water shrews are a mystery to many people. They lead a strange and fascinating life; awake 24 hours a day throughout their short lives, which are spent foraging for worms, snails and other morsels on the riverbanks.
Yet the problem with Neomys fodiens is that its common name, water shrew, is similar to the water vole, better known as the character of Ratty in Kenneth Grahame's story.
Another difficulty is that this shy insect-eater is seldom seen, despite being the largest of the domestic shrews.
It may also be rarer than previously thought, which is why the Mammal Society has launched a project to establish the true scale of its population for the first time.
Michael Woods, the society's chairman, said: "No one knows much about this charming little mammal; where they are found or what they need to live. We are concerned that they may be disappearing from our countryside due to habitat loss, pollution and pesticide use.
"We know that water voles have become rarer through the disappearance of their habitat, so there has to be a possibility that water shrews, which also have a semi-aquatic lifestyle, have been similarly affected.
"Virtually the only place where they are seen in the wild are watercress beds but that's because people working nearby notice them. Even signs of their presence such as footprints or droppings are rarely found because they spend much of their time swimming."
Potential causes of decline include the poor management of waterways and the fragmentation of riverside habitats which, in turn, isolates groups of water shrew. The Mammal Society hopes to gain a better impression of the water shrew population by enlisting volunteers to place plastic tubes baited with blowfly larvae next to streams and ponds for two weeks.
Mr Woods said shrews are naturally inquisitive andwill explore the tubes, find and eat the bait andleave droppings known as "scats". Collected scats will be posted to the Mammal Society for analysis.
By examining the insect remains in the scats, experts will be able to tell whether they have been dropped by a water shrew or a common or pigmy shrew.
Mr Woods said: "Resulting records will provide a baseline against which we can monitor future changes to the water shrew population. We will be able to establish their habitat and water quality preferences."
The Mammal Society, which is celebrating its 50th anniversary, plans to produce the first water shrew conservation handbook to help landowners and waterway managers to "retain this harmless small mammal as part of our modern countryside".Reuse content