Statistics and facts


Invasive non-native species are the second most significant cause of biodiversity loss on a global scale.

The total loss to the world economy as a result of invasive non-native species has been estimated at 5% of annual production (Pimentel et al 2002).

Globally, INNS have contributed to 40% of the animal extinctions that have occurred in the last 400 years (CBD, 2006).

Invasive non-native species are a known factor in 54% of animal extinctions and the only factor in 20%.

Over 80% of the worlds islands have been invaded by rodents.

95% of avian, 90% of herpetological, 70% of mammal and 70% of plant extinctions on islands is due to invasive non-native species.

20-30% of all introduced species worldwide cause a problem (Pimental et al 2001).

10 billion tonnes of ballast water is transported around the world every year.

84% of the world's 232 marine ecoregions reported the presence of invasive non-native species.

Introduction rates have been reported as high as two to three new species per year for Port Phillip Bay, Melbourne, Australia and up to one species every nine weeks for San Francisco Bay, California, USA.

In Europe, approximately ten new species become established each year and there is a rising trend for invertebrates and marine fish introductions (Hulme et al 2009).

The average lag-phase (time between introduction and successful spread and impact of a species) has been estimated at about 50 years, with a shorter lag-phase for tropical species than temperate species (Daehler 2009).

Great Britain

The total annual cost of invasive non-native species to the British economy is estimated at approximately £1.7 billion. This is said to be a conservative figure and does not include indirect costs which could be substantially higher.

Estimated total annual costs of invasive non-native species to England is £1,288,262,000, to Scotland is £250,144,000 and to Wales is £132,244,000.

2721 non-native species were counted England in 2005 for the English Nature report on 'Audit of non-native species in England', of which 1798 or 73% were flowering plants (angiosperms) and only 2.7% were marine species.

The GB Non-native Species Information Portal has 1800 non-native species registered. There are 1650 species when archaeophytes are removed. Therefore, approximately 44% of GB flora is native, and 56% non-native (51% neophyte, 5% archaeophyte [species which is non-native to a geographical region, but which was introduced in "ancient" times, rather than being a modern introduction. In Britain, archaeophytes are considered to be those species first introduced prior to 1492 A.D]).

An Audit of Alien Species in Scotland carried out by Scottish Natural Heritage identified 988 non-native species in Scotland.

56% of amphibian species, 30% of mammal species, 25% of reptile species and 13% of bird species in GB are non-native.

Almost two thirds of our non-native plant species in England are of European origin. The next most frequent continent of origin for terrestrial and freshwater plants is North America. Non-native freshwater fish species in GB originate mainly from North America and European/Asian continent equally. Australasia is the origin of 38 animals 9 plants that have become established in GB.

Plantlife's top 20 invasive non-native species which threaten the UK's flora include:
Aquatic species:Water fern (Azolla filiculoides), Fanwort (Cabomba caroliniana), Green sea fingers (Codium fragile), Australian Swamp Stonecrop (Crassula helmsii), Water hyacinth (Eichhornia crassipes), Floating pennywort (Hydrocotyle ranunculoides), Curly waterweed (Lagarosiphon major), Parrot's feather (Myriophyllum aquaticum), Water lettuce (Pistia stratoites), Giant Salvinia (Salvinia molesta).
Terrestrial plants: Few-flowered leek (Allium paradoxum), Hottentot fig (Carpobrotus edulis), Japanese Knotweed (Fallopia japonica), Shallon (Gaultheria shallon), Giant rhubarb (Gunnera tinetoria), Giant hogweed (Heracleum mantegazzanium), Spanish bluebell and hybrid (Hyacinthoides hispanica and H. hispanica x H. non-scripta), Himalayan Balsam (Impatiens glandulifera), False acacia (Robinia pseudoacacia), Rhododendron (Rhododendron ponticum).

The UK Technical Advisory Group on the Water Framework Directive have listed aquatic non-native species according to their level of impact. The table can be accessed by clicking here.

Japanese Knotweed

Total annual costs of Japanese knotweed to the British economy is estimated at £166 million.

Total annual cost of Japanese knotweed control at riparian habitats (excluding lakesides) in Great Britain was estimated at £5,636, 698.

£2m was spent to eradicate Japanese Knotweed on one 2 hectare development site.

9.2% of rivers and cannals in England and Wales are infested with Japanese knotweed and 3.1% in Scotland.

The total cost of controlling Japanese knotweed on the road network in Great Britain is estimated to be £5,095,894 (£3,901,393 in England, £437,416 in Wales and £757,085 in Scotland).

An insect called a psyllid is a new bio-agent to control Japanese Knotweed. Using an insect - which is a predator of the plant in Japan - to act as a natural form of pest control, will be the first time that a solution like this has been used to help control the spread of a non-native invasive plant in Europe and, if successful, could reduce the costs to the building and engineering industries of clearing this invasive plant. CABI – a world expert in natural control methods – have carried out extensive research into the best way to combat Japanese Knotweed with the least impact on the environment.  The psyllid was found on Knotweed growing wild in Japan and has now been tested in the UK on over 90 types of plants, focussing on closely related native species as well as important crops and ornamental species to ensure it does not attack other plants.  If the first phase is successful, the psyllid will be released at further sites where it will continue to be monitored.

Japanese Knotweed is listed by the World Conservation Union (IUCN) as one of the world's 100 worst invasive species. Click here for the full list.

Japanese Knotweed grows vigorously at a rate of up to a metre a month, including through tarmac, concrete and drains, causing damage to roads and buildings costing the millions of pounds to remove each year.

Other species

£13.9m of damage per year caused by deer vehicle collisions (many of which were non-native species).

£11m to eradicate rhododendron from a national park in Wales.

£25 million is the estimated cost of clearing the invasive Rhododendron ponticum from the Loch Lomond and Trossachs National Park.

£120,000 spent by one water works on modifications to cope with Zebra Mussels.

£160m estimated to be spent on weed control in one year in the UK.

£10m estimated cost to British timber industry of squirrel damage to beech, sycamore and oak woodland.

£1m delay was caused to a road development scheme while waiting to treat Japanese Knotweed.

A Scottish Government report estimated the potential Net Economic Value loss to Scotland of the introduction of the salmon parasite Gyrodactylus salaris at £633 million with severe consequences for rural communities.

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