Small rodents are common inhabitants of farmlands where they play key ecosystem roles but can also be major pests when overabundant, causing crop damages and significant economic losses. Agricultural landscapes are characterised by high fragmentation with remnant semi-natural habitats being typically restricted to narrow field margins. These linear habitats are key to maintaining local biodiversity, but can also harbour “irruptive pest” species, such as voles. The common vole Microtus arvalis, is a main vertebrate pest in continental European farmlands, and recently invaded the inland Mediterranean agricultural landscapes of NW Spain, where regular crop-damaging outbreaks now occur. Knowing how reliant common voles are on field margins in Mediterranean agricultural landscapes would be an important step forward for more targeted management. Here we report on common vole habitat use in Mediterranean European farmland and compare them with those found in northern latitudes, thus seeking for both general patterns as well as geographical differences. We conducted seasonal trappings over 6-years in the main habitats (cereal and alfalfa crops, fallows, and their margins). We show a strong edge effect, in the form of an exponential decay in vole abundance from the margin towards the inside of fields, and vole abundances 2.3 times higher in margins that inside fields. The magnitude of this edge effect varied depending on crop type, season and vole abundance (density-dependence). Cereal crops were characterised by a stronger edge effect than alfalfas or fallows (with abundance 8–10 times higher in margins than in fields during spring and autumn). Cereals appeared as the least optimal habitat for common voles, with important spill-over of voles inside the fields in summer when densities increased. Field margins, where vegetation characteristics hardly change seasonally, provide a limited (5% of the agricultural surface) but stable habitat and key refuge for common voles in Mediterranean farmlands. Our results suggest that targeting management actions in the field margins of cereal crops during spring and autumn and inside alfalfa fields during population increases should be considered in integrated control schemes of crop-damaging common vole outbreaks.