Introduced species of the British Isles

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Grey squirrel, an introduced species in Great Britain

Islands, such as the British Isles, can be adversely affected by the introduction of non-native species. Often an island will have several distinct species not present on the nearest mainland, and vice versa. The native flora and fauna of islands which have been isolated for a longer period of time such as New Zealand or Hawaii (which have been isolated for millions of years) are more vulnerable than islands such as Britain and Ireland, which became isolated more recently (8,000 years ago at the end of the last ice age).

Many species have been introduced to Britain during historical times. Some species such as the midwife toad (Alytes), rainbow trout (Oncorhynchus mykiss), sweet chestnut (Castanea sativa) and horseradish (Armoracia rusticana) have been introduced with no adverse consequences. However, others such as the eastern grey squirrel (Sciurus carolinensis), signal crayfish (Pacifastacus leniusculus), and Japanese knotweed (Fallopia japonica) have had a severe impact both economically and ecologically.

Problems caused[edit]


In 2010 CABI (Centre for Agricultural Bioscience International) estimated that introduced species in United Kingdom cost £2 billion annually.[1] The most costly species were listed as being the European rabbit and Japanese knotweed. The European rabbit, introduced to Britain in the 12th century, eats and therefore damages a wide variety of crops and cost the UK £263 million. Japanese knotweed, introduced as an ornamental garden plant in the late 19th century, the roots of which spread by underground rhizomes, can undermine and damage buildings, pavements and roads,[2] cost £179 million. In fact, most mortgage lenders in the UK will demand proof of the plant's eradication from a home owner's property(if signs of it being present are noticed), for it can cause potential physical damage to one's estate.[3]


Displacement of native species[edit]

In addition to the economic costs incurred by management, some introduced fauna displace native species. This can occur by predation, competition for resources, or the spread of disease.

The native European crayfish
The introduced signal crayfish

Predation: American mink (Neovison vison), which either escaped or were released from fur farms, prey on native European water voles (Arvicola amphibius) and are drastically reducing their numbers.[4] It was reported that since the late 1980s, 90% of the UK population of the European water vole has been lost, primarily due to displacement and predation by the American mink.[5]

Resource competition: The introduced grey squirrel is larger and more aggressive than the native red squirrel (Sciurus vulgaris) and displaces the native squirrel by competing for food and habitat. Rose-ringed parakeet (Psittacula krameri) populations, originally an Afro-Asian parakeet, have become established in Britain from introduced and escaped birds. There are two main populations: the largest is based around south London, where they can be regularly seen in places such as Battersea Park, Richmond Park, and Greenwich Park; the smaller population can be seen in Surrey and Berkshire, and by 2005 consisted of many thousands of birds, known as the Kingston parakeets.[6] These large parakeets displace native birds species by competing for roosts and nest sites.

Disease: Some introduced species carry diseases to which native species are susceptible. The grey squirrel is a carrier of the squirrel pox virus which kills red squirrels but not grey squirrels.[7] The European crayfish is susceptible to crayfish plague which is spread by the introduced signal crayfish.[8]

Unlike some other environmental problems such as pollution, the effect of an introduced species is not a single event. Once a species has been introduced to an island, the problems may persist and escalate as the species spreads further.

Environmental damage[edit]

Coypus (Myocastor coypus), large semi-aquatic rodents native to South America, were introduced to the British Isles in 1929 when fur farms were set up in Sussex, Hampshire, Devon and Norfolk. The farms were sited mainly in lowland areas rich in rivers and streams. During the 1930s coypus escaped from captivity and despite repeated attempts to control them, they adapted well to the British habitat, breeding successfully in the countryside of East Anglia. Their habit of building large burrows in river banks caused great erosion damage and threatened the tourism industry where boating is a popular recreation, and caused great damage to drainage works. Coypu were declared to have been successfully eradicated in December 1989,[1].[9] but in 2012 a "giant rat" was killed in County Durham, and authorities suspected that the animal was, in fact, a coypu.[10]

Management of introduced species[edit]

Some species have adapted harmoniously into the ecology of the British Isles. For example, the little owl is not native to the British Isles but was first introduced in 1842,[11] by Thomas Powys and is now naturalised there. However, the presence of some introduced species has proved disastrous for native flora and fauna. There is often a link between how well a species can integrate with an existing ecosystem, and the distance from their local range; i.e. species sourced closer to the sink site tend to cause less damage.[citation needed]

Case studies of impact examples can be found at the Non-native Species Secretariat website.

Information on control methods for aquatic species can be found at the GB Non-native Species Secretariat website.

Example: Grey squirrel[edit]

One notable example of a species introduced to the British Isles is the grey squirrel from North America, which out-competes the smaller native red squirrel, as well as carrying a virus that is fatal to the reds. The cost of attempting eradication was reported in 2010 to be £14 million.[1] These attempts have been deemed unsuccessful and priority is now being given to preserving the remaining red squirrel habitats.

The following is a partial list of introduced species:




Butterflies and moths[edit]


Two species that prey on earthworms.



See also[edit]



  1. ^ a b James Meikle (2010-12-15). "Rabbits named Britain's most costly invasive species | Environment". London: The Guardian. Retrieved 2012-03-24.
  2. ^ "managing invasive non-native plants" (PDF). Environment Agency. Archived from the original (PDF) on 2012-06-17. Retrieved 2012-04-19.
  3. ^ "Invasive plants in the United Kingdom that may lead to offence and fees from the UK government". Fantastic Gardeners. Retrieved 2016-02-19.
  4. ^ "Mink and Water Vole – GB non-native species secretariat". Retrieved 2012-03-24.
  5. ^ "Water vole sanctuary created in Bridport". 2013-03-08. Retrieved 2013-03-08.
  6. ^ London Bird Report 2006. London Natural History Society. 2006. p. 93. ISBN 0-901009-22-9.
  7. ^ "Squirrel Pox – GB non-native species secretariat". Retrieved 2012-03-24.
  8. ^ "Crayfish plague". Environment Agency. 2012-01-30. Retrieved 2012-03-24.
  9. ^ Gosling, Morris (4 March 1989). "Extinction to Order". New Scientist. London. 121 (1564): 44–49.
  10. ^ "Police To Investigate Man Who Killed 4ft Rat". Sky. Archived from the original on 25 April 2012. Retrieved 9 March 2013.
  11. ^ Greenoak, Francesca (1997-10-31). British Birds: Their Names, Folklore and Literature. Christopher Helm Publishers Ltd. ISBN 0-7136-4814-7.
  12. ^ a b c Various introduced animal species
  13. ^ a b "Examples of problem non-native species in Scotland". 2012-02-14. Retrieved 2012-03-24.
  14. ^ Powered by Intergage "The British Deer Society – Chinese Water Deer". Retrieved 2012-03-24.
  15. ^ "Science & Nature – Pets – Cats". BBC. 2004-03-12. Retrieved 2012-03-24.
  16. ^ "Remains of Roman rabbit uncovered". 2005-04-13. Retrieved 2013-03-09.
  17. ^ British Deer Society
  18. ^ "Mammal status – Feral goat". Retrieved 2012-03-24.
  19. ^ "GB non-native species secretariat". Retrieved 2012-03-24.
  20. ^ British Deer Society
  21. ^ BBC Wildlife finder – Sika Deer
  22. ^ British Deer Society
  23. ^ W. J. Sutherland & G. Allport (2009) The distribution and ecology of naturalized Egyptian Geese Alopochen aegyptiacus in Britain, Bird Study, 38:2, 128-134, DOI: 10.1080/00063659109477080
  24. ^ a b c Michael McCarthy, The I Newspaper, Saturday November 3rd, 2012, p. 21
  25. ^ "BBC News – Salmon fears after crayfish found in River Kelvin". 2010-11-26. Retrieved 2013-03-09.
  26. ^ "New threat to box plants". The Royal Horticultural Society. Retrieved 23 June 2011.
  27. ^ Brown, David C G; Barron, Scott J (2016). "The Captive Rearing of Common Forest Looper Pseudocoremia suavis Butler, 1879". Atropos (57): 17–21. ISSN 1478-8128.
  28. ^ Forestry Commission UK, information on Oak Processionary Moth