The UK’s 10 most dangerous invasive plants and animals

There isn’t a single country on earth that doesn’t have some kind of invasive plant or animal species, but there are a few small isolated islands that remain untouched. Unfortunately they will surely all succumb to an infestation of some kind one day, as more people going to more areas of the world means a higher chance of a single seed or animal hiding in the right place. Officially there are several dozen invasive plant and animal species in the UK, but no one knows the exact number as there are many micro-invasions that involve a few patches of something that can only be found in one area of the country. Below are some of the worst offenders, who combined have cost the UK billions in damages and wiped out a number of native species.

American signal crayfish

These were originally brought over to be bred for their meat, but they escaped their ponds and lakes and spread into the natural water systems of the country. The UK’s native white-clawed crayfish were widespread at the time, but the larger American ones not only used them as a food source but also carry a fungal infection that is deadly to the white-claw species. Today it is illegal to catch the native white claws as they are highly endangered, but American signal crayfish continue to spread across the country, occupying an estimated 70% of all river and canal systems.

Giant Hogweed

One of the most dangerous invasive species to humans, this plant can grow up to 3.5 meters tall and often grows around the edges of water, blocking off entire sections of the bank. The reason it’s so dangerous is because there is a sticky sap that covers the stems and leaves which contains a toxin called photosensitizing furanocoumarins. This hard-to-pronounce chemical causes severe burn-like wounds on the skin, often accompanied by large blisters and an intense itching and burning sensation. The lasting effects of the sap can include scarring across the affected area, and re-occurrence of the burning and itching, which apparently can last for life.

Asian Hornet

These aren’t quite as big or nasty as some of the hornet species that live in hotter countries, but they are making themselves at home in numerous countries around the world and aren’t showing signs of slowing down. They are actually slightly less aggressive than the UK native common wasp, but they are physically bigger and stronger, which makes them a threat to much-needed native species like bees which they compete with for territory and food.

American bullfrog

This large species of frog is responsible for the extinction of several other species around the world and is classed as one of the most destructive invasive animals. They are prone to developing a disease that is more deadly to other marine life, which has caused the deaths of billions of other types of amphibious creatures. Apart from killing other animals just by being in the same body of water, these huge creatures eat almost non-stop, constantly looking for food and depleting sources for other animals.

Japanese knotweed

The tall and unusual-looking plant known as Japanese knotweed was purposely brought to Britain by the Victorians who thought it would make an interesting showpiece for the garden. The plant is very strong and can grow through roads and pavements, and sometimes damage the structural integrity of buildings. It is illegal to purposely plant it anywhere and it costs the UK economy over £150 every year just to control.

Grey Squirrel

This invasive species is responsible for almost wiping out the native red squirrel population, but not in the way most people think. The common belief is that they simply out-bred the red squirrels and depleted their food source, but the truth is that grey squirrels carry a type of pox virus that doesn’t seem to affect anything other than red squirrels, to which it is very deadly. Whenever a group of grey squirrels moves into new territory, they can slowly kill off the native reds just by being there, and the competition for food becomes secondary.

American mink

Originally brought over to be bred for their fur, these sneaky little sausage rats escaped into the wild and started to breed. Mink are strictly carnivores and will eat anything from frogs to birds and their eggs. They are very stealthy and excellent swimmers, so nothing is off the menu, and in the areas of the world they are native to, they frequently attack creatures like turtles and snakes. The mink is believed to be a major factor in the 90% plus decline in the UK’s native water vole population.

Carpet sea squirt

First noticed in Britain in 2008, this tiny organism grows in connected patches that can stretch for several kilometers. It’s thought to have arrived here after getting stuck to the bottom of a boat somewhere and has since established itself in large areas around the coast. Because the patches are so dense, they can smother other marine life like shellfish and coral, eventually becoming thick enough to deprive them of food and movement, ultimately killing them off. Due to it being so hard to detect and treat, it seems the problem is going to get much worse before it gets better.

Quagga mussel

This type of freshwater mussel spreads rapidly and often grows in connected patches. They are currently in only a small number of river systems, but they are already costing the economy millions each year. They grow around the insides of pipes that outlet into rivers, and eventually become thick enough to block them. There is currently an active effort by the government to locate and remove quagga mussels from the water systems before the problem gets out of hand.

Himalayan balsam

This purple-flowered weed isn’t directly dangerous to other plants or animals, but it does spread faster than any of the other plants on this list. One of its nicknames is popping weed as the seed pods explode when they are ripe enough, pinging seeds in various directions. The threat it makes to other plants is to simply out-grow them and block off the light and deprive the ground of certain nutrients needed by other plants. The one good thing about this plant is the seeds can be eaten straight from the pod when they are ripe, tasting like grain with a weak nutty flavor.