2007 vole plague in Castile and León

The 2007 vole plague originated in early summer 2006 in the province of Palencia, located in the autonomous community of Castile and León, Spain. By the summer of 2007, rodent populations had severely devastated crops in the plateau fields. Following a summer marked by significant agricultural losses, the density of voles decreased by September 2007, leading to the institutional declaration that the plague was over. However, vole populations remained abundant in the months that followed. It was only the winter frosts and low temperatures in November and December that reduced their numbers to normal levels.

The common vole (Microtus arvalis) was primarily responsible for the crop devastation across the northern plateau. This Eurasian species had previously been confined to the Cantabrian Mountains, where it differentiated into the subspecies called Microtus arvalis asturianus. Over time, it expanded its habitat southward, escaping its natural predators, particularly birds of prey. Under normal conditions, the population of common voles did not exceed 100 million; however, estimates for the summer of 2007 suggested their numbers had surged to at least 700 million. The voles affected approximately 500,000 hectares of crops, resulting in estimated losses of 15 million euros. Their voracity led to their characterization as a significant agricultural pest in Castile.

The plague affected the entire community of Castile and León, with the provinces of Valladolid, Segovia, Palencia, and Zamora experiencing the most severe impacts. The areas of Tierra de Campos and the region bordering Tierra de Medina were particularly affected, extending into the municipalities of Aliste and nearing the border with Portugal.