ARCHIVE: Examples of non-native species in the UK
Aquatic plants - Ludwigia grandiflora
The water primrose (Ludwigia grandiflora) Ludwigia which is currently unmanageable in France , is an aquatic plant native to South America . It can spread rapidly and the very dense mats which it forms can present a threat to many aquatic species by depriving the submerged plants below of light, causing problems for aquatic invertebrates, clogging waterways and exacerbating flooding risks. It can lead to more algal growth in more static water and crowd out the space needed by fish. It may also provide perches for cormorants and herons, leading to increased predation.
In 2006, Defra commissioned the Centre for Ecology and Hydrology to trial methods to eradicate the weed (helped by the Environment Agency). The signs are that as the trial continues the "problem" is diminishing and complete eradication may well be feasible.
Japanese knotweed is native to Japan, Taiwan and China, and was introduced to Europe as an ornamental plant in the early 19th century. It is a large vigorous weed that appears to have no natural enemies in Britain. It can colonise most habitats and is regarded as a troublesome pest in many parts of the country because of its rapid invasion and domination of habitats, which results in the exclusion of other plants.
North American Ruddy Duck
Information on the Ruddy duck can be found at
The grey squirrel was introduced into this country from North America in the 19th century and has spread widely, especially in lowland areas, with a population now estimated at over 2 million. They are regarded as pests by a number of groups because of the damage they cause to woodland. They are largely responsible for the decline of the red squirrel in England because they are stronger and more adaptable than the red and they carry the Squirrelpox virus, which is lethal to red squirrels.
Introduced non-native fish such as Zander and signal crayfish can have direct effects on native species, for example by predation, or can upset the natural ecological balance. Non-native fish can also introduce novel diseases and parasites to which our native populations may have no resistance. In addition to the 1981 Act, further legal controls on the keeping of non-native crayfish were implemented in 1996. In England and Wales, The Prohibition of Keeping of Live Fish (Crayfish) Order 1996 was made as an Order under the Import of Live Fish (England and Wales) Act 1980. See the efishbusiness website and information on non-native fish and crayfish.
A desk study (PDF 500KB) of the status of parakeets in England has been published.
Page last modified: 14 January 2011
Page published: 23 October 2008