Governments try to ban alien invaders

New neighbour: North American signal crayfish are loose in the UK and damaging the ecosystem.

When foreign plants and creatures arrive in a country they can do great damage to the environment. Governments are trying to stop them. But should we be interfering with nature at all?

Less than five years ago they came on ships from the Black Sea. They entered Britain’s rivers and canals, killing many types of fish and spreading deadly parasites. Carried by unsuspecting anglers, they are now rapidly colonising the country’s freshwater. This dangerous alien is a crustacean, the ‘demon shrimp’, and environmentalists say we should be very afraid.

It is just one of 1,875 non-native species found in the UK in 2012, 282 of which are ‘invasive’ and threaten native species and delicate ecosystems. MPs have warned that the current UK laws to deal with them don’t work. The European Union has now drawn up a list of dangerous species threatening its members and placed a ban on owning, transporting, selling or growing them.

Experts say that many insects, plants and animals worldwide are threatened with extinction by foreign rivals who are arriving faster than ever. The North American signal crayfish has caused a rapid decline in the British variety. Japanese knotweed is overwhelming native plants as well as destroying buildings and roads. In just ten years, the imported Asian harlequin ladybird has wiped out almost half of its British cousins. The bill for all the damage done runs into billions every year.

Trying to control new species is often a losing battle. Some eventually become accepted, like the grey squirrel which arrived in the UK from the US in the 19th century bringing diseases that devastated the native red squirrel.

Some biologists say this process is simply ‘survival of the fittest’ and it is foolish for humans to try to intervene. They note that mankind has always moved plants and animals around the world for its advantage. Horses were introduced to the Americas in the 16th century and potatoes and tomatoes brought back to Europe. Once coffee only grew in Africa, now it is cultivated in over 70 countries. Tea and rubber plants have also travelled far beyond their original homes.

Global shipping allows species to move further and faster than ever before. Does it make sense to try to keep out invaders? Is it even possible?

Natural eviction

Some say that nature is always evolving and we should not oppose it. Humans are naturally conservative and are frightened by change, but now that Britain is used to grey squirrels, for example, few people see them as a pest.

Yet others think that this side-effect of global trade is altering ecosystems that have taken thousands of years to create and are easily overwhelmed. Rabbits introduced to Australia in the 18th century are now an enormous pest causing millions of dollars of damage to crops every year. We must have stronger international controls to prevent such irreversible disasters.

You Decide

  1. Should we try to control the movement of species?
  2. ‘We only care about controlling species when we find them ugly.’ Do you agree?


  1. In pairs, watch the BBC video on ‘killer’ shrimp in ‘Become an expert’, then design a poster warning river users about their danger and how to look out for them.
  2. Using Carl Zimmer’s piece in ‘Become an expert’, list three ways non-native species can benefit an ecosystem and three ways in which they can be harmful.

Some People Say...

“Mankind is like a gardener who plants weeds with the flowers and puts snails among the vegetables.”

What do you think?

Q & A

I don’t care about wildlife.
Changes to the ecosystem could have catastrophic knock-on effects. Bees are vital for pollinating crops to feed us, but their numbers are decreasing. To make matters worse, some environmentalists fear that Asian hornets, which are four times larger than bees, might arrive in Britain and further decimate the population. They are already in France, where they killed five people last year.
What stops species from spreading anywhere?
The migration of species is limited to areas where everything in the environment is right for them to survive. Normally predators evolve which keeps the numbers of a species in check. However, if a species is suddenly introduced into a new environment without predators it can increase rapidly.

Word Watch

A parasite is a species which depends for its survival on another species without doing it any good. Fleas need dogs, but dogs certainly don’t need fleas.
A group of creatures which includes crabs, lobsters, prawns and shrimps.
Natives belong to a region, non-natives come from elsewhere.
Controlling invasive species can prove very difficult. In the 19th century Europeans introduced rats to Macquarie Island in Australia which thrived due to a lack of predators. Cats were introduced to solve the problem, but they decimated the native birds. When the cats were exterminated, rabbit numbers exploded, damaging vegetation.
A law from the 1930s said that anyone who found a grey squirrel in their garden must report it to the authorities so that it can be exterminated. Last month, ministers admitted defeat and finally repealed it.
The phrase, which Darwin incorporated into the fifth edition of On the Origin of Species, refers to species with the traits that are most likely to help them survive and prosper in their environment.
Today Brazil is the world’s largest producer of coffee, followed by Vietnam.


PDF Download

Please click on "Print view" at the top of the page to see a print friendly version of the article.