Europe's worst guests: Ducks and furry rodents

Furry rodent-like nutria and herds of Asian deer may look cute but are among 1,000 invasive species that have disturbed ecosystems, threatened native animals and left governments across Europe with hefty damage bills, scientists said Monday.

In a new paper, scientists estimated that at least 1,000 of Europe's 10,000 invasive alien species of animals, insects and plants have caused substantial environmental or economic damage.

Montserrat Vila of the Donana Biological Station in Seville, Spain, lead author of the study, said the damage caused by invader species can be as serious as the effects of climate change.

The paper, published Monday in Frontiers in Ecology and the Environment, the journal of the Ecological Society of America, lists Europe's worst natural guests and details the damage they cause - decimating crops, upsetting ocean food chains and worsening human health problems like hay fever.

"I would say that not all alien invasive species are a problem, but some of them are very damaging and have properties which make things difficult for other species - by causing changes to the ecosystem, or by eating them," Vila said, speaking by telephone from Spain.

Invasive species are often introduced by humans, either intentionally - like cultivating plants for horticulture- or accidentally, with parasites carried by other species or marine organisms arriving in ships' ballast water.

Governments across Europe have acknowledged the problems posed by invasive alien species, including those detailed in the new report.

Britain spends at least euro150 million ($194 million) per year tackling 30 types of alien weeds and sees an estimated euro3.8 billion ($4.9 billion) in annual crop losses caused by invasive insects and animals and disease-carrying pathogens, the report said.

Among the most damaging invaders are ruddy ducks, which have rapidly increased in British waters and now threaten the white-headed duck, Europe's rarest duck, due to interbreeding. A similar invasive pest is the Silka Deer, common to Asia but now found in Scotland, which also threatens the native red deer population through breeding.

Across Europe, euro27 million ($34.9 million) has been spent to protect marine birds from new predators and each year problems associated with alien marine algae cost about euro8.18 million ($10.6 million).

In Italy, about euro2.8 million ($3.6 million) is spent controlling nutria, or coypu, a South American semi-aquatic rodent sometimes known as the beaver rat, which was introduced to Europe by fur ranchers. With white whiskers, and bright orange teeth, the unlikely looking pest can destroy vegetation and disrupt irrigation systems with its burrowing and often carries the nematode parasite, which can infect humans.

The study said Italy has also spent euro1.06 million ($1.4 million) in a failed attempt to control an influx of Asian long-horned beetles, cutting down 2,000 trees in suburbs around Milan.

The paper warned that some invasive plants produce allergenic pollen which could lead to an increase in hay fever among humans.

But the report does not produce a single damage estimate from by all invasive species, largely because Vila estimates scientists are only aware of about 10 percent of the damage caused in Europe.

"The impacts of many invaders go unnoticed," Vila said in a statement. "These changes can be irreversible, and many are as important as the changes caused by climate change or pollution."

Vila's study used data compiled by the Delivering Alien Invasive Species Inventories for Europe (DAISIE) project, commissioned by the European Union in 2005 to detail more than 10,000 invaders.

Robert Sweeting, an Honorary Research Fellow at Freshwater Biological Association, said as globalization increases, new invasive organisms will appear and add additional costs.

But Mick Crawley, a professor of plant ecology at Imperial College in London, said while Vila's conclusions merit further study, the view that all alien species are harmful is not true.

"There is a kind of racism involved that all alien species are harmful," he said. "I certainly don't think that aliens species in general have measured negative economic impact."