Sorex aranaeus

Order: Eulipotyphla

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Description: Common shrews are tricoloured: dark brown on the back, pale brown at the sides and whitish underneath. They have dense velvety fur, a long pointed nose, tiny eyes, small ears and red teeth. The main visible feature distinguishing them from mice and voles is their pointed and prehensile nose. The easiest way of distinguishing them from other shrews is by size. They are larger than the pygmy shrew but smaller than the water shrew. The fur on their back is dark brown as opposed to the blacker fur of the water shrew and the paler brown fur of the pygmy shrew. They also have a less hairy tail.

Size: Head and body 48-80mm, tail 24-44mm. Tail is approximately 50% of body length.

Weight: 5-14g.

Lifespan: They have a very short life span and it is uncommon for them to survive for more than 12 months.

Breeding: Females will normally have three or four litters of 5-7 young between April/May and September. They are promiscuous so the litter may have more than one father. The young are weaned and independent within 22-25 days. Young shrews have occasionally been seen forming a caravan behind their mother, with each grasping the base of their sibling’s tail. This may be associated with a disturbance of the nest or may be a way of introducing the young to their environment.

Habitat: Can be found almost anywhere – parks and gardens, hedgerows, farmland, woodlands, grassland, etc.

Diet: Mainly insects and spiders but also earthworms, small slugs and snails. Need to eat regularly, at least every 2-3 hours as they have a high metabolic rate. They need to eat 200-300% of their body weight each day.

General ecology: Shrews are very territorial and only socialise during the mating season. Each shrew will have a territory of about 300-600m². They are active both at night and in the daytime and do not hibernate in winter, though they do become less active. Because they need to eat regularly they may often be seen foraging. They make their nests underground or under dense vegetation, often using burrows formerly used by other small mammals. They have a good sense of smell but poor eyesight.

Distribution and main sites: Widespread in the UK except for Northern Ireland and some outlying islands (e.g. Shetland and the Outer Hebrides). A recent estimate puts the number of common shrews in Great Britain at over 40 million. Distribution on the above map mainly reflects local surveys but these resourceful animals may be seen almost anywhere. Widely distributed in Shropshire but under-recorded.

Local survey history: Small mammal surveys are regularly carried out in various locations, including Whitchurch, Shrewsbury, Preston Montford, Ironbridge and Wenlock Edge, often by, or on behalf of, organisations such as Shropshire Mammal Group, National Trust, Shropshire Wildlife Trust or Ironbridge Meadows Group. Sufficient suitable bait such as blowfly larvae or casters must be provided.

Conservation status: Common shrews are not an endangered species, but they are protected under Schedule 6 of the Wildlife and Countryside Act (1981).

Threats: Main threats to their survival are changes in land use, loss of hedgerows, woodland and green corridors. Pesticides, herbicides, etc., are also a threat. They also have various predators including cats, owls, foxes and other birds of prey. 

Main recording methods: Small mammal surveys are carried out, under licence, using humane traps (Longworth and/or BioEcoSS tube traps) to record the population of specific areas. Special care should be taken when trapping shrews as the risk of death is much higher than with other small mammals due to their high metabolic rate. Trapping should only be carried out under licence. Longworth traps are often used with shrew holes to allow shrews to escape. Common field signs include burrows and pathways in undergrowth. Bones and fragments may be found in owl droppings, for example, but may be difficult to identify. Shrew remains are more commonly found than those of other small mammals as they have glands that excrete a foul-tasting liquid that some predators, particularly cats, find distasteful.

Did you know? During the winter when they become less active, a shrew’s body shrinks so that they need less food to survive. Their overall body mass may shrink by up to 18% but their brains may shrink by up to 30%. A study run by Nanjing University in 2019 found that shrews were capable of echolocation using high frequency noises and close-range spatial orientation.

Acknowledgements:

Text – Charlotte Huntly, with particular thanks to the Mammal Society, wildlife trusts and Wikipedia; with additions by Malcolm Monie

© Shropshire Mammal Group 2020