This year’s Invasive Species Week has now wrapped up, but we shouldn’t stop there! We need to continue raising awareness about invasive non-native species and their impacts to protect our native mammals.
What is the difference between invasive species and non-native species?
Non-native species are species that have been introduced to Great Britain by people – there are over 2000 animals and plants that are non-native to GB. While most of these species are harmless, a subset of these non-native plants and animals have devastating impacts on our native wildlife. These are known as invasive non-native species. There are over 200 known invasive plant and animal species in Britain, with a number of these being invasive mammals – a number that continues to increase year by year.
In what ways can they be a problem?
Invasive mammals may have negative impacts on the environment, our health, as well as our economy. Invasive mammals can compete with native wildlife for food and habitat, as well as prey on our small native mammals.
Invasive mammals include:
The American mink was brought to GB and Ireland by humans, and later escaped or misguidedly released from fur farms in the 1950s and 1960s. This small carnivore is an active predator, and preys on anything it is large enough to catch – which includes our native water voles and seabirds.
This has caused severe damage to the water vole population, where water voles are now among the 1 in 4 mammals that are under threat of extinction.
There are mink control projects all across the UK that are trying to recover the species that have been affected. These projects use mink monitoring rafts to establish if mink are present in an area, and once detected, mink are trapped and humanely dispatched.
The grey squirrel was first brought from the USA to GB in 1876 and released into the wild by the Victorians. They quickly outcompeted our native red squirrels, covering 300 miles between Argyll and Stirlingshire in Scotland within the first 25 years of its introduction in GB. On top of out-competing them, the grey squirrel carried with them diseases that spread to the red squirrel population. While grey squirrels appear to be immune to the squirrel pox (Papapox virus) that they carry, the disease is fatal for the red squirrel.
Grey squirrels have also been observed to strip the bark off trees to feed on the softer inner layers. This can cause serious damage to our native trees such as beech trees, possibly even killing the trees or distorting their growth depending on the level of damage caused.
Native to Taiwan and China’s Hainan region, the Reeves’ Muntjac was introduced to Woburn Park, Bedfordshire in 1894. They were then deliberately released into the surrounding woodlands from 1901 onwards, where a combination of releases, translocations and escapes saw the wide establishment of Muntjac deer populations in Southeast England.
Muntjac deer can cause serious damage to important wildflowers such as honeysuckle, which creates a knock-on effect for the small mammals and other wildlife that depends on it for food, nectar and nest sites.
There’s a new non-native species in town…
Greater White-toothed Shrew
In 2021, a new species of non-native mammal was discovered in Sunderland, England – the Greater white-toothed shrew; a species known to be invasive in Ireland. Their rapid spread in Ireland meant that it was not necessarily surprising that the shrew found its way to Great Britain, but this development is worrying as it is clearly associated with the disappearance of the native pygmy shrew in Ireland, and across other islands in Europe. More information about this can be found in the webinar recording below.
While only recently discovered, there is evidence that the greater white-toothed shrew has been in Great Britain from at least 2015. More information needs to be gathered about this shrew, as well as other small mammals, to truly assess how far the greater white-toothed shrew have spread, and if and how they are impacting our native small mammals.
Other invasive species to look out for:
What can be done?
For other invasive species, you can help us build a picture of non-native mammal population size and distribution in Britain. You can do this by downloading the Mammal Mapper app and recording the wild animals you see while out and about or recording historical sightings using our online form.
For better understanding the spread of the greater white-toothed shrew, you can help with our Searching for Shrews project. Keep an eye out for more information on how to get involved with this project! Hint… it involves owls!
To learn more about the mysterious greater white-toothed shrew, watch our special Invasive Species Week webinar:
You asked and ‘Shrew God’ Allan McDevitt answered:
Learn more about which species you should be on alert for to help prevent the establishment of a new invasive non-native species.