We examined whether the body size of mound building wood ant Formica aquilonia workers is affected by forest clear-cutting in a before-after logging field study. Clear-cutting is expected to decrease the availability of tree-living aphids, the main food resource of wood ants. Worker size decreased from one year to the next in clear-cuts but not in forest stands, indicating food limitation in the clear-cuts. Worker size increased with nest size in forest interiors, but not in clear-cuts, which further indicates food limitation in the clear-cuts. In addition, lower body-fat contents in ant workers in the clear-cuts supports previous suggestions of lower food resources after forest logging. Nests were cooler in the clear-cuts, which suggest that they may be poor habitats for forest-dwelling wood ants. Food resource limitation may have an effect on the ability of wood ants to regulate nest temperatures.