The numbers "have increased markedly in recent years," the French National Institute for Agronomic Research (Inra) said in a press release.

From 2000-2007, on average 19 "exotic" species established themselves in Europe each year, compared with only 10 each year between 1950 and 1975, it said.

Asia, followed at a distance by North America, is the major source for these alien species.

Less than 10 percent of the newcomers were deliberately introduced into Europe.

The rest either hitched a ride in container vessels, trucks and planes through international trade, or migrated to Europe and discovered a habitat niche due to today's warmer climate.

Overall, Europe has 10,822 alien species, if fish, birds, mammals and vegetation are included. Around two-thirds of the aliens are plants.

They include worrisome pests, such as the Asian tiger mosquito (Aedes albopictus) as well as long-established denizens, such as the common carp (Cyprinus carpio), a native of East Europe and Asia that has spread across the European continent.

The list is being compiled by 15 European institutions in a consortium under the name DAISIE (Delivering Alien Invasive Species Inventories in Europe), on (http://www.europe-aliens.org/).

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