Mammal Week 2019 - Lesser white-toothed shrews

Shrewly awesome!

by Carl Knight

Hi my name is Carl and I am a volunteer here at the Mammal Society. I have just completed my undergraduate degree in Mathematics at the University of Sussex and am hoping to go on to complete a Masters in either Zoology or Ecology.

I have always found shrews fascinating so for Mammal Week I am writing about the little known lesser white-toothed shrew. The lesser white-toothed shrew (Crocidura suaveolens), is a tiny shrew with a widespread distribution in Europe, parts of Asia and North Africa. The Mammal Society‘s 2018 recent review into the Population and Conservation Status of British Mammals and subsequent Red List listed the lesser white-toothed shrew as ‘Near Threatened’ in Great Britain overall, and specifically in England. Although this species was likely introduced to Britain by Iron Age traders from France or northern Spain it has since naturalised. However, currently it is only found on the Isles of Scilly, Jersey and Sark.

What’s in a Name?

Although their species name means ‘sweet smelling’ (suaveolens), quite the opposite is true! In fact, their pungent smell is often the best indicator of presence; so much so that they are also known as the ‘musk shrew’ because of the strong smell they produce to mark their territories.

Most shrews have red-tipped teeth due to the presence of iron in the tooth enamel. However, as their name suggests, lesser white-toothed shrews have white teeth instead! They also have light grey-brown fur, large ears and bristly hairs interspersed with long, white ones, covering their tail. Interestingly, the name (Crocidura) means "woolly tail”!

How small?!

Also eluded to in its name is its size. There are two white-toothed shrews, the lesser and greater, with, you guessed it, the lesser being smaller than the greater. Lesser white-toothed shrews range from 7.5-13.5 cm in length with the tail making up roughly a third of this. Although not the smallest shrew, it is still extremely light, weighing just 6 grams on average! To put that into perspective, a 10 pence coin weighs exactly 6.5 grams. In comparison, greater white-toothed shrews (Crocidura russula) range from 9.5-15.5cm in length and weigh about 12.5 grams on average.

Lesser and greater white-toothed shrews are commonly confused species and are very hard to tell apart. In Great Britain, greater white-toothed shrews are only found in Ireland, but they are not native there. In a 2014 study, Allan McDevitt (a Mammal Society Council Member) and colleagues modelled the rate at which the greater white-toothed shrew was expanding across Ireland. McDevitt et al. found that the invasive shrew was expanding at a rate of 5 km per year, and now occurs in seven counties in Ireland (Tipperary, Limerick, Cork, Waterford, Kilkenny, Offaly and Laois). This is endangering the native pygmy shrew which simply cannot compete for resources with this much larger species of shrew.

To read the full paper: https://doi.org/10.1371/journal.pone.0100403 

Even smaller?!

Mating usually occurs from March to September and 2-4 litters of up to 5 pups are born after a gestation period of 24-32 days. The young weigh only 0.5 g at birth but are weaned at about 4 weeks and the female may be pregnant whilst still feeding her last brood. Lesser white-toothed shrews are born blind and thus like common shrews, a female lesser white-toothed shrew and her young may form a "caravan" when foraging for food or seeking a place of safety; each shrew grips the tail of the shrew in front so that the group stays together.

You can see this amazing phenomenon below!

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