MONTPELLIER, FRANCE // Behind air-tight doors in a lab in a southern French city, scientists in protective coveralls wage war against a fingernail-sized danger.
Lurking in net cages is their foe: the Asian tiger mosquito, capable of spreading dengue fever and other tropical diseases in temperate Europe.
First spotted in Albania in 1979, the black-and-white striped invader has gained a foothold on Europe's Mediterranean rim and is advancing north and west, according to captors' reports.
Colonies are established in 20 European countries, in moderate climes as far north as Germany, Belgium and the Netherlands.
"The risk of disease is very low but it is growing," the entomologist Jean-Baptiste Ferre said at France's leading mosquito-control institute.
"The more mosquitoes there are, the higher the risk."
The Asian tiger mosquito can spread many kinds of viruses.
They include dengue, which can result in a deadly haemorrhagic fever, as well as West Nile virus, St Louis encephalitis and a painful disease of the joints called chikungunya.
The insect transmits the virus by taking blood from a sick person and handing on the pathogen the next time it takes a meal.
The worry is that the insect will spread disease in Europe by biting infected people arriving from tropical countries where the viruses are endemic.
From Montpellier, Mr Ferre and his colleagues at the Entente Interdepartementale pour la Demoustication en Mediterranee (EID) monitor the spread with some 1,500 traps dotted around France.
Mr Ferre points to maps that begin in 2004, when a tiny red dot represented the first settling of the mosquito in France around Menton, near the Italian border.
Year by year, the dot grows into red tentacles that probe north and west.
The insect has a flight range of only about 200 metres, so it hitchhikes a ride in cars, lorries and traded goods.
