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Read the article and find out where these animals came from, where they invaded and who or what they caused problems for.
Hоw much danger are we in? How many moaners are there?
Imagine you run a small food shop in your local neighbourhood. Suddenly, a giant supermarket opens for business opposite your shop. What happens to you and your business?
In the natural world, things are often the same. The red squirrel was living happily in England when, in the 1880s, many people brought grey squirrels from North America as pets. Since then, these pets have escaped into the wild. They now eat the same food as the red squirrels, and they eat it more quickly. Consequently, now there aren't many native squirrels in England and they are in danger of extinction.
There are many invaders that don't cause extinctions, but they do destroy plants and harm the economy. For example, European red deer are destroying the forests in South America because they eat the young trees. Rabbits have spread from Europe and now eat farmers' crops all over the world. These kinds of invaders are causing problems for humans, unlike the grey squirrels, which cause little damage to plants and don't damage the economy.
Few invaders are large land animals; most of them are fish or small animals like insects. There are thousands of these invaders and these smaller animals often mean farmers lose a lot of money. The apple snail from South America doesn't cause much damage in Europe, but it causes a lot of damage in southeast Asia because it loves to eat rice plants.
There are very few positive sides to these animal invasions. However, in Britain today, one invasion story offers some hope. Chinese mitten crabs first came on ships from China. These crabs destroy local environments and attack fish in fish farms. However, in China these crabs are an expensive food, so, now, Britain is selling them back to China. The crabs are travelling on ships again, but this time they are food, not invaders; and this time they are helping the British economy, not harming it.