Rural northern Spain has been stricken by a plague of millions of voles that have devastated lettuce, potato and barley crops and threaten to invade vineyards, public parks and even urban centres.
Farmers in the high plateau around Leon, north of Madrid, have demanded massive doses of poison to exterminate the ubiquitous rodents. But health workers and environmentalists warn that the cure might be worse than the disease, with poison threatening wildlife and posing a worse risk for humans than piles of dead voles.
Hundreds of exasperated farmers, carrying live voles, protested outside the regional government headquarters in Valladolid this week, breaking a glass door with the intention of freeing the creatures into the offices. But police charged and scattered the demonstrators. The authorities later met the farmers and listened to their grievances.
"We've been suffering this situation for nine months and it's getting worse," complained Donaciano Dujo, spokesman for the regional farmers' association. "We demand that the authorities eradicate this pest and compensate us for the damage to our crops." In some areas 80 per cent of crops have been lost.
The common vole (Microtus arvalis) is native to northern Spain. Most of the population dies in the region's bitter winters, but they survived this year, which was unusually ice-free, then flourished in the rainy spring that followed.
"We are experiencing the peak in a demographic explosion of voles," said Juan Jose Luque, a vole specialist at Valladolid University's rodent evolution department. "Eventually all these cyclical populations end up declining. That will happen this time." But the animal - which used to be confined to the Pyrenees, and the Picos de Europa that back Spain's northern coast - is gradually conquering the central plain. The traditionally arid tableland has in recent years been brought under cultivation through irrigation. This more hospitable habitat, plus an untypically warm and wet year, "could explain the current population surge", Dr Luque said. Under current conditions, female voles give birth every 30 days, producing a litter of at least four.
A total of 20 people have been treated for the infectious disease tularaemia, caused by contact with rodents, whose symptoms include fever, headaches, muscle pain, shivering, coughing and weakness. Large areas have been treated with anticoagulant rat poison, which killed voles but also hares, rabbits and wood pigeons, which could be dangerous to humans if eaten.
Local children have developed their own anti-vole technique. "You surround them with two or three of us, then stamp on them or hit them with a stick," said Alvaro Garcia, 11. Every night Alvaro and his friends go hunting in Fresno del Viejo, one of areas near Valladolid worst affected, and despatch some 200 voles.Reuse content