2007 vole plague in Castile and León

The 2007 vole plague began in early summer 2006 in the province of Palencia, in the Spanish autonomous community of Castile and León. In the summer of 2007, crops in the plateau fields were devastated by rodents. In September 2007, after a summer of severe losses, the density of rodents decreased throughout the community and the plague was institutionally considered to be over. However, there was an abundance of voles during the following months. Only the winter frosts and the low temperatures of November and December reduced vole numbers to normal.

The common vole (Microtus arvalis) was responsible for devastating the crops of the northern plateau. This Eurasian species had only penetrated the Iberian Peninsula as far as the Cantabrian Mountains, where it differentiated and became a subspecies called Microtus arvalis asturianus, beginning to extend its habitat to the south, thus freeing itself from its natural predators, the birds of prey. In normal years, their population did not exceed 100 million, but in the summer of 2007, it is estimated that they reached at least 700 million. They devastated a total of 500,000 hectares of crops and caused losses of 15 million euros. Their voracity led them to be described as the scourge of Castile.

This plague was present throughout the community of Castile and León, the most affected provinces being Valladolid, Segovia, Palencia and Zamora, especially in the areas of Tierra de Campos, and the area bordering Tierra de Medina, where other provinces such as Salamanca and Avila converge. It also came to be located in the municipalities of Aliste, on the verge of crossing into Portugal.