Invasive species ABC

Top of the list for invasive mammalian species list are the grey squirrel, American mink, and sika and muntjac deer. These are the species that are most widespread and can cause significant damage if left unchecked. Let’s take a closer look…

Grey squirrels displace native red squirrels and are carriers of squirrel pox virus. While the virus doesn’t affect grey squirrels, squirrel pox is deadly for red squirrels and can quickly decimate whole populations. Grey squirrels also damage trees, which can have a huge impact on commercial forestry as well as the habitats they invade.  A lesser known fact is that greys also predate on bird eggs and chicks.

BASC’s Natural Capital Report estimates that the current level of grey squirrel control delivered by the shooting sector saves around £32 million in carbon, enhancing the success of tree planting and natural regeneration. Shooting saves a further £1.4 million’s worth of timber and wood fuel by preventing bark stripping by grey squirrels.

Anyone who has ponds or rivers running through their shoot or property has most likely dealt with American mink and knows exactly how much damage these mustelids can cause. They prey on everything and anything from domestic poultry, gamebirds and fish to small mammals. American mink have been directly linked to the drop in water vole population, driving the latter to near extinction in the UK.

While Sika and muntjac deer make for some great eating, they also do quite a lot of damage. Muntjac are prolific breeders, which helps them spread fast. They are also highly adept at consuming ground flora and young trees to clear all but the bare ground behind. 

Apart from causing serious damage to woodlands and ground flora, Sika are a danger for our native red deer as the two can hybridise. It is thought that only a handful of red deer populations across the UK remain pure.

Deer as a whole do substantial damage to woodland, and deer management in the UK is estimated to save more than £171 million in carbon by allowing young trees to grow. A further £11 million in timber and wood fuel is saved by the current level of deer culling. You can find more statistics on the benefits of shooting in our Natural Capital Report. 

Let’s move on to the least obvious non-native invaders. While the likes of flatworms native to New Zealand and Australia, North American bullfrogs, quagga mussels and Asian hornets may seem too small to cause much trouble, they are in fact very dangerous.

New Zealand and Australian flatworms can now be found throughout the UK and prey on our native earthworms. Earthworms are crucial for the overall health of our soils, as well as all the species who depend on them as a food source. 

North American bullfrogs are big predators which threaten several smaller native amphibians, fish, small mammals and even birds. Meanwhile, quagga mussels pose a threat to native biodiversity, with the ability to alter whole freshwater ecosystems. They can also grow in pipes and on ships, making them quite the nuisance. 

Some of our most recent invaders are Asian hornets, which specialist in hunting pollinators, especially honeybees and bumblebees. They pose a significant threat to our native bees, who have no defence mechanisms against this aggressive, predatory insect. Asian hornets should be reported immediately here when spotted, and you shouldn’t attempt to destroy them or their nests by yourself.