It’s not just plants that are invasive species, animals can cause similar harm to the environment and economy. Invasive species in the UK have significant economic costs, in addition to their environmental impacts. The cost of invasive species to the UK economy is estimated to be around £1.7 billion per year. This cost is due to a combination of factors, including the cost of controlling and eradicating invasive species, the loss of native species and habitats, and the impact on tourism and recreation.
One of the most well-known invasive species in the UK is the grey squirrel, which was introduced from North America in the late 19th century. Grey squirrels are carriers of squirrel pox which they are immune but is deadly for reds. The greys are much more prolific breeders and they also damage, or kill, many native broadleaf trees by stripping the outer bark so that they can eat the softer wood underneath. As populations of grey squirrels has risen over the years, the red has become a rare sight.
Muntjac, a small deer from China and Taiwan, was brought to Great Britain in 1831 to be kept in collections, but is now common across most of England and parts of Wales. Their grazing can have serious impacts in woodlands where they clear shrubs and prevent tree regeneration, affecting other wildlife including birds and butterflies.
American mink, which was introduced for fur farming in the 20th century, and now preys on native birds, fish, and small mammals.
The American bullfrog has earned a reputation for being one of the countries most harmful invasive amphibian species. Not only does it feed night and day on a wide range of prey, it also carries a disease that has led to widespread amphibian decline and several global extinctions.
In the past bullfrogs have been kept as pets and later released into the wild – it is advised not to release unwanted pets as this could be bad for the animal and can cause much harm to native wildlife.
Sacred ibis, a bird from Africa, was popular in European zoos in the 1970s and 80s, and established free-flying colonies within their grounds. Escaped individuals are a serious problem for other wildlife, as they eat fish, small rodents, amphibians, and the eggs and young of other bird species including terns. A number of individuals have been spotted wild in Britain.
Topmouth gudgeon, a small fish originally from eastern Asia, breeds quickly and harms both native and farmed fish by eating young fish and eggs and spreading disease. The Environment Agency is working to eradicate it from a small number of ponds where it has been introduced.
Signal crayfish are found throughout England since their introduction and in high densities cause extensive damage to banks and eat most plants and small animals found in and around the water. They outcompete our native white-clawed crayfish and also pass on a fungal disease called ‘crayfish plague’ which is harmful to our native species and can be spread by wet footwear and equipment.
Efforts to control and eradicate invasive species in the UK have been ongoing for decades. Control measures include manual removal, chemical control, and biological control.
- Manual removal involves physically removing invasive species by hand or with machinery, which can be effective for small infestations.
- Chemical control involves the use of herbicides and pesticides to kill invasive species, but can have unintended impacts on native species and the environment.
- Biological control involves the introduction of natural predators or pathogens to control invasive species, but can also have unintended impacts on non-target species.