Top 10 Invasive Non-Native Species

Published on 25-02-2014 by Dr Paul Beckett

Japanese knotweed (Fallopia japonica) was introduced to the UK by the Victorians. It has now spread across the country to be found in isolated stands in most areas (see distribution maps here). It out-competes native plants and forms dense monocultures. Often found on waste land, on railway banks, and alongside watercourses, if left uncontrolled it can cause damage to walls and built structures.
Japanese knotweed is, however, not the only invasive non-native species causing problems in the UK. Below is a list of ten other species that are causing problems:

• American mink (Mustela vison) – this species escaped from fur farms, or was deliberately released, and now has been linked with a decline in native water vole populations, as well as habitat destruction;
• American signal crayfish (Pacifastacus leniusculus) – Is a deadly threat to the native white clawed crayfish, not only for out-competing them for habitat and food, but also for spreading a deadly ‘crayfish plague’;
• Creeping water primrose (Ludwigia grandiflora) – This plant, with a bright yellow flower, has spread across France, Belgium and Holland and there are concerns that it could do the same in the UK;
• Floating pennywort (Hydrocotyle Ranunculoides) – It has established itself on watercourses, out-competing native species and making leisure activities difficult;
• Giant hogweed (Heracleum mantegazzianum) – often found in waste land or along waterways, the sap from cut plants can cause painful blistering, particularly when the skin is exposed to sunlight;
• Himalayan balsam (Impatiens glandulifera) – Often found along the side of waterways, it is the tallest, annual, flowering plant in Britain, reaching 3m in height, forming dense monocultures out-competing the native vegetation;
• Known as the ‘killer shrimp’ (Dikerogammarus villosus) – This species kills a large range of freshwater animals such as native shrimps and even young fish;
• Parrot feather (Myriophyllum aquaticum): This species is originally from South America but has spread to numerous sites across the UK, forming dense mats over watercourses, starving other species of light and nutrients;
• Topmouth gudgeon (Pseudorasbora parva) – This small fish from Japan has introduced disease into still waters that prevent other species from spawning;
• Zebra mussels (Dreissena polymorpha) – Native to southern Russian freshwater lakes, these mussels often outcompete and kill native species – they also clog up water works causing significant damage, which often necessitates water companies employing divers to remove them by hand.