Frequently asked questions

Here you can find answers to some frequently asked questions about non-native species. More specific FAQs related to aquatic  and riparian weeds and specific species can be found via the menu on the left.

What is the definition of a ‘non-native species’?
A non-native species (NNS) is a species that has been introduced into the country by human intervention (either deliberately or accidentally) since the end of the last ice age (approx ten thousand years ago). The term 'non-native species' is synonymous with alien, non-indigenous, foreign and exotic.

How many non-native species are there in Great Britain?

A recent study has shown that there are are nearly 2000 established non-native species in Great Britain.

Are all non-native species a problem?
Most non-native species do not cause problems, indeed the majority of our agricultural species (wheat, barley, sheep etc.) are not native to Britain. Only a minority become invasive and have negative impacts. Some, however, have seriously negative impacts on agriculture, forestry or biodiversity interests.

What are invasive non-native species?
Invasive non-native species are species that have been introduced (deliberately or accidentally) by man which are having a detrimental impact on the economy, wildlife or habitats of Britain. There are far more non-native species present that are not invasive.

Why are invasive non-native species an issue?

After habitat loss, invasive non-native species are the second biggest threat to biodiversity worldwide, and on islands are considered to be the biggest threat.        

Where do most of our invasive non-native species come from?

Invasive non-native species come from all over the world, some from continental Europe (e.g. Zebra Mussels) some from Asia (e.g. Chinese Mitten Crab), some from America (Grey Squirrel, Mink, Ruddy Duck, Ludwigia, Signal Crayfish), some from Africa (Hottentot Fig) and some from Australia (Australian flatworm) and New Zealand (NZ Pigmyweed, NZ flatworm).        

How do non-native species get to Britain?

Non-native species spread through a variety of pathways some of which are intentional (e.g. deliberate release of non-native fish species for angling) and some unintentional (e.g. by ‘hitch-hiking’ on food or other goods imported into Britain or by escaping from captivity (e.g. American mink)). Some marine species are transported large distances attached to ships or in ships ballast water (e.g. Chinese mitten crabs).  Many plant species are brought in intentionally as part of the horticulture trade but some then become established in the wild after they are disposed of irresponsibly or ‘escape’.           

Are they increasing and spreading?

There is already a large number of non-native species in Britain and the number becoming established is likely to increase due to the growth in world trade and global tourism.  Climate change may also allow species that are currently benign in Britain to become invasive. The risks associated with invasive non-native species are therefore likely to remain a feature of our lives.

What are the main impacts on native species?
Invasive non-native species can have a huge range of negative impacts.  These include:

  • Transmission of disease to native species (e.g. grey squirrels with squirrel pox, Signal crayfish with crayfish plague).
  • Competition with native species (Harlequin ladybird).
  • Predation on native species (Mink on water voles).
  • Increased flooding risk (invasive water weeds).
  • Infrastructure damage (e.g. to bridges, water treatment facilities).
  • Human health risks (oak processionary moth (which have hairs that are irritants to humans), giant hogweed (that has sap that causes blistering) and terrapins (which can carry Salmonella)).

How much do they cost the British economy?
The cost to Great Britain is at least 1.7 billion per annum (Cabi Report). This does not include less-quantifiable costs to biodiversity and ecosystem functions.

What is the worst invasive non-native species in Britain?
There are a number of species which have a significant detrimental impact.  Some of these are economic impacts while others have negative impacts on our wildlife.  Examples of some of the worst species are given below:

  • Japanese Knotweed, which can grow through concrete, costs developers millions of pounds per annum, mainly on brownfield sites.
  • Rats have wiped some seabird species off a large number of British islands.
  • American mink are the main cause of the catastrophic loss of water voles in Britain.
  •  A number of non-native aquatic weed plants clog watercourses, kill off fish stocks, prevent angling and can increase flood risk and damage structures such as bridges.

 [NOTE:  The EA have published a list of their top 10 problem species and they are (in order of importance):  Japanese Knotweed, American Signal Crayfish, American Mink, Giant Hogweed, Floating Pennywort, Himalayan Balsam, Australian Swamp Stonecrop, Chinese Mitten Crab, Parrots Feather, Topmouth Gudgeon].

Are all non-native species going to be eradicated?
Firstly the non-native species framework strategy is concerned with prevention as this is by far the most effective means of tackling the problem of invasive non-native species.  Secondly, the strategy is concerned with addressing only those non-native species that are know to be, or are thought to present a significant risk of being invasive.  Finally, it is internationally recognised that eradication is usually only practically feasible and financially affordable in the early stages of an invasion.  Once invasive species are well established, it is usually a case of mitigation measures and control e.g. localised or possibly regular removal.

Can we really do anything about non-native species?
Yes, there is a lot that can be done both by government and the public to help reduce the risks of introducing or spreading invasive non-native species.  The strategy sets out the measures the GB Administrations will take to raise awareness and understanding of the risks, to gather information and to minimise the risks of further introductions or establishment of invasive species.  Key organisations covering a wide range of interests from business to hobbies can help inform their members about these issues and everyone can generally adopt more responsible attitudes and behaviours when it comes to using non-native species in gardens or keeping exotic pets.  Government can ensure that there are adequate  inspections on imports to detect invasive species and can support research and management of invasive species where appropriate.

What research has government carried out on invasive non-native species?
GB administrations and agencies have been carrying out research on a range of non-native species issues for many years.  This has ranged from strategic research (e.g. assessing the use of fertility control techniques) to work on individual species (e.g. rabbits, parakeets, ruddy duck, mink) including looking at impacts on native species and methods of control. 


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