Invasive Species that Call the UK their Home

Vegan Life looks at the invasive species that call the UK their home and the impact that they have on our native species


Our ocean planet is speckled with islands and the ever-changing nature of Earth means that new islands are being created and destroyed as the Earth’s techtonic plates snail towards, against or apart from each other. These islands can be thousands of miles from the nearest continent and many are still incredibly isolated.


However, as the human species has developed, the world seems to have become smaller and less diverse. The ease of world travel has enabled us to live in ways which were unimaginable just a few hundred years ago and although the benefits of globalisation are undeniable, our cross continental movements have also had an unexpected impact on our environment.


Human activities including trade, horticulture and farming, have not only allowed us to travel to new places but have opened up wildlife corridors for animals and plants to move between islands which were previously unreachable. This type of exploration seems to be part of human nature and since the industrial revolution, the scale, regularity and spatial reach of global travel is now so extensive that species movement is becoming a problem.


It is estimated that there are nearly two thousand invasive species in Great Britain, many of which are having a devastating impact on our native species.


According to Dr. Tony Martin, Professor of Animal Conservation at the University of Dundee, invasive species are: “Organisms, which can be anything from bacterium to a camel, that have been introduced by man, to environments where they didn’t evolve.”


Islands like the UK are particularly susceptible to the negative impacts of invasive species. In total land area terms, islands represent less than 5 per cent of the world but, interestingly, over 60 per cent of all extinctions have taken place on islands and invasive species have been implicated in 86 per cent of these extinctions.


Islands are ecologically significant and the Galapagos Islands were famously studied by Charles Darwin in his study of evolution through natural selection. Island ecosystems evolve independently from the mainland and therefore, their flora and fauna evolves to survive in that particular habitat with defence mechanisms tailored to the particular predators and threats in that environment. This process has been happening over millions of years and the longer that an island has been isolated for, the more vulnerable the island becomes to the potentially devastating impacts of invasive species.


New Zealand or Hawaii, for example, have been isolated for a much longer periods of time than the UK and therefore invasive species pose a formidable threat to their biodiversity. The threat to New Zealand is deemed so perilous that they have set aside 28 million dollars to eradicate rats, stoats and possums and the country aims to become predator-free by 2050 in an effort to conserve their bird populations, which have not evolved to protect themselves from these non-native species.


japanese knotweed


In the UK, some of the most successful invasive species include Japanese knotweed, rhododendron, Himalayan balsam, floating pennywort, muntjac and signal crayfish. But perhaps the most famous example is the deliberate introduction of grey squirrels from North America in the 1870s. Grey squirrels have been so successful partly because of their ability to out-compete, due to their larger size, but they also carry a virus which is fatal to native red squirrels and the latter native squirrels are now fairly rare around most of Great Britain, save Scotland where conservation efforts have been relatively successful.


Invasives, like grey squirrels, have obvious impacts on native species through direct predation, out-competing, transmitting diseases and killing offspring but their indirect threats can have an even wider impact on the environment including changing food webs and decreasing biodiversity to create monocultures or species dominance. Although, not all invasive species are detrimental to the environment. Some ‘desirable’ invasives, such as Mandarin ducks, work in harmony with the environment and actually boost biodiversity.


grey squirrel


Researchers have found that species with certain traits are more likely to become dominant. Fast growth, rapid reproduction, high dispersal and ecological competence (the ability to tolerate different environments) are some of the indicators that a species may become dominant when introduced to a new location — studies indicate that, in some circumstances, adaption to a new environment can occur within as little as 20 generations.


Many of the alien species in the UK were accidentally introduced due to lack of awareness about the possible impacts. Horticulture enthusiasts introduced many alien species including Japanese knotweed, a perennial plant which was introduced in 1825 as an attractive ornamental plant. Its invasive roots mean that it can damage concrete foundations of buildings and roads making it, now, undesirable.


Another lesser known example of invasive plant species is giant hogweed, part of the cow-parsley family originating from South-West Asia, which is now widespread across Great Britain after it was introduced around 200 years ago by horticulturalists. Each plant can produce up to fifty thousand seeds per year and therefore it is incredibly tenacious. Giant hogweed is quite attractive with its impressive, towering stems and enormous, white flower clusters but giant hogweed actually produces a phytotoxic sap which can cause excruciating burns on skin. These burns are exacerbated by UV rays in daylight and can take months to heal. Additionally, the effects of the burn can be felt for years after the initial burn.


Giant hogweed is also dangerous to animals, especially when ingested, and if your companion animal eats part of the plant or its seeds, make sure you take your companion to the vet immediately. It can also cause blindness if it gets into your companion’s eyes.


giant hogweed


Eradicating giant hogweed and Japanese knotweed is a difficult process, but there are few ethical concerns to consider. Eradicating an animal species, on the other hand, is not so clear cut.


American mink may be one of the most successful alien species in the UK with estimated population of over 100,000 individuals. With no native mink to compete with, the American mink found their niche on our riverbanks.


The American mink was first introduced, from North America, to Great Britain in the 1920s when mink farms were used to cultivate fur on a large scale. Their fur was highly valued due to the quality of their soft, luxurious fur which is longer and denser than the European Mink’s. Mink farms peaked in 1962 when there were around 700 farms in the UK but, thankfully, the last farm closed in 2003 after the introduction of the Fur Farming Prohibition Act 2000. However, a wild population exploded after mink farm escapes and deliberate releases and the American mink is now an established species in the UK.


After human introduction less than 100 years ago, mink are now being hunted down, trapped and killed. The reason? American mink have decimated populations of ground nesting birds such as terns and black-headed gulls, as well as water voles, which have declined by over 90% in the last fifty years. For this, the mink have propelled themselves to the top of the eradication hit list.


american mink


According to Natural England: “Mink can be effectively trapped in the mating season (February to March) and when their young leave the den (August to November).” You can trap these animals on your property and you can subsequently shoot them using a suitable firearm and ammunition. The Game and Wildlife Conservation Trust state on their website: “Once exposed in a trap a mink may scream loudly and incessantly until it is dispatched.”


Eradication of invasive species is controversial. Some believe that eradication of an alien species is the lesser of two evils; the culling of the non-native species is necessary to ensure ecological stability and to protect the native species from extinction. Dr Piero Genovesi, Chair of IUCN Invasive Species Specialist Group, said: “Invasives are threatening many species around the world. They are the first cause of species extinction for many taxonomic groups like amphibians or birds and this is a problem which is a huge concern for many areas around the world.”


But is wiping the whole population out the best option? It could be argued that we should let nature take its course. The world is not static and environmental change is a natural, expected process in the animal kingdom. In fact, scientists believe that some native species are able to adjust to the introduction of invasives. For example, Snakes in Australia have successfully adapted to the introduction of the poisonous cane toad by developing smaller mouths which makes them unable to eat the largest, most poisonous toads.


It should also be noted that the eradication of invasive species can be detrimental to native animals. Professor Tony Martin spoke at the 2017 Invasive Species Conference in Dundee about the eradication of rats and mice from South Georgia. The island in the South Atlantic is home to the native Pipit, the world’s most southerly songbird, which was being decimated by the rodents as a result of introduction by whalers. Toxic pellets were spread using a helicopter to eradicate these animals from the island. Professor Martin said: “None of the native wildlife suffered damage at a population level.” But when questioned further he admitted: “There will be non-target mortalities.”


The eradication worked and South Georgian Pipits have returned to the island. However, is it fair for us, as a species of the earth, to populate an animal on an island, knowingly or not, and then kill them a few decades later? Some would argue that a man-made problem needs a man-made solution. Indeed, many of the invasive species which are now becoming ‘problematic’ were initially introduced to their new environments by human activities.


Signal Crayfish were introduced in 1975 to provide aquaculture for Scandinavia. However, this attractive commercial species carried the deadly crayfish plague to the UK which is responsible for the crash in white-clawed crayfish, nearly driving the native species to extinction. They also predate salmon and trout eggs and are often described as aggressive in their search for new territory. Consequentially, there have been attempts to introduce a disease which would only affect the signal crayfish, which failed, but attempts to wipe out the species through trapping or species specific disease continues.


signal crayfish


This problem should not be blamed on signal crayfish and they should not be culled for man’s mistake, just as American mink should not be eradicated for following their natural predatory instincts.


Ethics aside, eradicating invasive species is an expensive business. The cost of management of alien species is thought to be around 1.7 billion pounds per annum and we now have species from every continent in the world, apart from Antarctica, in the UK.


If invasive species must be managed, non-violent methods need to be explored more fully and further research needs to be conducted so that scientists can better understand the areas which alien species are most likely to inhabit so that potential hotspots can be mapped.


Also, assessment and promotion of successful mitigation measures will help to stop invasive species being transported to island ecosystems. The import and export of plants and animals, especially, need to be monitored aggressively to ensure that invasive pathways are not created across the ocean or land boarders. New research has found that screening protocols on boarders are becoming more accurate, reducing new introductions and have been shown cost-effective. These methods, however, are too late for American mink and signal crayfish, among many others.


It seems unfair that some invasive species, like mandarin ducks, are acceptable and others, like American mink, are not. The environment was not made to be designed and pruned by humans and eradicating some invasive species for behaving naturally is unfair, counterproductive and cruel. The deliberate culling of thousands of blameless individual animal is wrong, invasive alien species or not.


These examples show the folly of using wild animals for commercial gain; humans are responsible for these invasive species, yet, predictably, the animals are the ones who end up losing.




The lifestyle magazine written by vegans for vegans.