Access Science: The taming of the greater white-toothed shrew is essential

The invader is out-competing the indigenous pygmy shrew, and there could be serious repercussions for our ecosystem

An invasive shrew species is spreading rapidly across the south and midlands, in the process driving out the native pygmy shrew. This is bad news for the local shrew, but the unwanted arrival could have a much bigger impact on our ecosystem.

The greater white-toothed shrew first appeared along the north Tipperary border in 2009 or 2010. Since then, it has spread along the Shannon up to Birr, east to Carlow and south into Cork and Kilkenny, says Dr Liam Lysaght, director of the National Biodiversity Data Centre.

“It is out-competing the indigenous pygmy shrew, so where the newcomer is colonising, we have evidence the pygmy shrew is extinct locally,” he says. “The pygmy is the smallest mammal we have, about the size of your thumb. The greater white is about double this size.”

You would need patience to spot the indigenous shrew, as it keeps a low profile, he says. “People see them when brought in as cat prey.” You might also assume that the arrival of the invasive species doesn’t really matter, but you would be very wrong.


"It is a bad thing. It is out-competing the pygmy, so it is likely to alter the ecological balance in an area," says Dr Lysaght. For example, there is growing evidence that the invader is having an impact on the nestling success of the barn owl, a species much higher up the food chain.

When present, the owl preferentially hunts the white-toothed shrew, but the species is poor nutritionally; it is akin to a human eating nothing but hamburgers, he says. “Where barn owls are feeding on them, owl productivity is in decline. This negative impact on owls is a good example of how an ecological change can have unexpected consequences.”

Dr Lysaght would like to know if you spot shrews of any kind.

Log your sightings: An app that allows users to assist in monitoring nature

A free app makes it easy for citizen scientists to participate directly in the work of the National Biodiversity Data Centre. The centre is an initiative of the Heritage Council and is responsible for recording and monitoring plant, animal, insect and bird biodiversity. People who spot a shrew or any animal or bird can log the sighting using the app, and this will be validated and added to the logs of what species are seen where. You can even upload a picture if you are unsure of the species you have seen, whether it was on the run, in the air or even as roadkill.

"This helps to identify species that may be in decline," says Liam Lysaght of the National Biodiversity Data Centre. "A sighting of a badger or pine marten can contribute to this conservation effort." More than 1,000 people have so far contributed to the Atlas of Irish Mammals, which records 113,000 logged sightings. Online it offers real-time data capture, and a hard copy is to be published in 2016. Contribute to the Atlas at submitrecord.php


  • Question: Why are 10 per cent of people left-handed? Sheelagh MacHugh
  • Answer: All primates have hand preferences, and, in evolutionary terms, right-handedness is a relatively recent invention. The more primitive the primate, the more likely it is to be left-handed. Lemurs tend to be left-handed, old-world monkeys are evenly split between left and right, 35 per cent of chimpanzees are left-handed and only 10 per cent of humans are lefties. Science does not yet know for sure why 10 per cent of people are left-handed. The most common hypothesis points to the structure of the brain, which is divided into two hemispheres, with individual bodily functions being controlled primarily by one hemisphere. Language and using our hands (fine motor skills) are two of the most energy-intensive human activities. It is more efficient to control these two activities from a single brain hemisphere. Most people have their language-control functions in the left hemisphere and it follows that fine motor control is located there too. Each brain hemisphere generally controls the opposite side of the body, and therefore most people are right-handed. William Reville, UCC
Dick Ahlstrom

Dick Ahlstrom

Dick Ahlstrom, a contributor to The Irish Times, is the newspaper's former Science Editor.