Last year, I wrote an article about how we used pine marten (Martes martes) scats or faeces to detect the DNA of small mammals that the pine marten had been feeding on. These small mammals included the wood mouse (Apodemus sylvaticus), pygmy shrew (Sorex minutus), bank vole (Myodes glareolus) and greater white-toothed shrew (Crocidura russula). In that article, I also wrote about work from Ian Montgomery and colleagues at Queen’s University Belfast that reported that the native small mammals like the wood mouse and especially the little pygmy shrew were being displaced by the presence of the introduced bank vole (introduced in the 1920’s) and the recently introduced, greater-white toothed shrew (discovered in 2007).
A new PLOS ONE study produced by Allan McDevitt (University College Dublin) and colleagues from a number of institutions have now modelled the rate at which the greater white-toothed shrew is expanding across Ireland. McDevitt found that the invasive shrew is expanding at rate of 5 km per year, and now occurs in seven counties in Ireland (Tipperary, Limerick, Cork, Waterford, Kilkenny, Offaly and Laois). McDevitt and colleagues trapped the shrews in habitats like hedgerows, and in core areas up to 50 shrews were caught along 200 m stretches. In areas like this, the little pygmy shrew simply cannot compete as both shrews are insectivores and the larger greater white-toothed shrew consumes more of the available prey.
McDevitt describes the greater white-toothed shrew as being slightly smaller than the standard mouse that people are used to seeing in their houses (it weighs between 8 -14g), but the most distinctive features of the shrew are a pointy nose and sharp white teeth. They can infest houses, and according to McDevitt “you’ll know if you have the greater white-toothed shrew as the males have foul smelling glands that release a scent to attract females for mating”. The native little pygmy shrew is rarely, if ever seen indoors, and weighs as little as 2 – 3g. In areas where the greater white-toothed shrew is common, cats are also said to be bringing them to their owners on a regular basis.
McDevitt believes that people might be accidentally facilitating the movement of the shrews as they are often associated with farm buildings and houses, so they could for instance get moved around with livestock, hay or even building or gardening materials. This is also the most likely way in which the shrews initially arrived in Ireland, and France or Spain are said to be the most likely sources as it does not occur in Britain.
But what is the future for the pygmy shrew in Ireland? Chances are it could become extinct. According to McDevitt this would be a travesty for Ireland as it is one of the European strongholds for the species, and has been present here for thousands of years. Despite the excellent science used to study the distribution and expansion of this species, science has no solid answers to halt the spread of this animal. The best way to prevent further invasions like this is to tighten our border security, and to create greater public awareness about the risks that invasive species pose to our native biodiversity.
McDevitt, A., Montgomery, W., Tosh, D., Lusby, J., Reid, N., White, T., McDevitt, C., O’Halloran, J., Searle, J., & Yearsley, J. (2014). Invading and Expanding: Range Dynamics and Ecological Consequences of the Greater White-Toothed Shrew (Crocidura russula) Invasion in Ireland PLoS ONE, 9 (6) DOI: 10.1371/journal.pone.0100403
Other sources include the UCD Press Release and the Today FM Ray D’Arcy Show from June 24th.