The database for the "DAISIE" project is the first of its kind, as it not only logs all current invaders, but also possible invaders of the future. It was launched at a meeting in Portoroz, Slovenia on 23 January.
"Not all alien species in Europe are invaders," explains David Roy at the Centre for Ecology and Hydrology, UK and an expert for DAISIE. To be classified as an "invader", a species must cause economic damage or threaten local biodiversity. There are 10,677 alien species on DAISIE, of which roughly 10% are invasive.
For alien species, the most common route into Europe or into a new European region is hitching a ride on a truck, car, ship or plane. Transportation alone is responsible for nearly 10,500 introductions, most of which are unintentional.
Apples and pears
Not so for the Harlequin ladybird, however. It and more than 6000 others have become aliens in Europe by being intentionally introduced into new habitats. The Sika deer from East Asia, for instance, was released as game. Others are pets that either escaped, such as the rose-ringed parakeet, or were intentionally released by their owners.
The Harlequin ladybird, Harmonia axyridis, was released in northwestern Europe in the hope that it would control aphids. But with females producing up to 50 eggs each day during its reproductive season, the species soon spread.
In fact, Harlequin ladybirds have exactly the opposite effect to that intended. They decrease farmers' gains from apples and pears because once the aphids get scarce, the ladybirds feed on the soft fruit. They also cluster on grapes and can end up in the wine, releasing alkaloids and affecting its bouquet.
Pufferfish dish
Another invasive species can be deadly when it enters the human food chain. Lagocephalus sceleratus, also known as the silverstripe blaasop, can kill if eaten without being prepared properly by a specialist chef. Originally from south-east Asia, it is a cousin of the pufferfish eaten by the Japanese as a dish called fugu.
The silverstripe blaasop arrived into the Mediterranean from the Red Sea, through the Suez Canal. "As soon as we found out that we have them in Israel, the fisheries department put a leaflet out to fishermen telling them not to sell the fish but to throw them back at sea," says Bella Galil, of Israel Oceanographic and Limnological Research.
In 2004, eight people died after having eaten the invading pufferfish in Egypt, and by 2005, it had made its way to Crete. The fish have been picked up on market stalls in Greece, where authorities are struggling with how to alert the population without spreading panic. The pufferfish is now spreading westwards along the north Mediterranean coast.
Canals are the second most important means of marine species getting into Europe, after ships. Another worrying species to have infiltrated the Mediterranean through the Suez canal is Rhopilema nomadica, the giant nomadic jellyfish.
With a girth of up to one metre across, it has been making summer appearances since the mid-1980s. Most individuals are about 60cm across but they aggregate into huge swarms that are more than 100km long. Although they will not kill you, "they are very venomous;, their sting is like being burnt by hot iron," says Galil.
Dark side
Swarms put a halt to certain types of net fishing because they fill the nets, making it impossible for the fishermen to sort their catch. And in 2001, Israel Electric had to scoop tonnes of jellyfish out of the cooling pool of its power plant at Hadera, which cost it $50,000.
Commenting on the DAISIE list, David Roy warns: "The total number of alien species was a surprise. Equally important is the rate of addition of new species. It is not slowing down -, if anything the problem is getting worse."
"Imports such as the venomous black widow spider tell us about the dark sides of globalisation," says Wolfgang Nentwig, of the University of Bern in Switzerland. "Alien species do not enrich our environment but are, after habitat destruction and global warming, the main threat to biodiversity.