Are spring mass migrations of bumblebees and wasps driven by vole cyclicity?

In search for factors which could drive the spectacular spring migrations of pre-reproductive queens of bumblebees and social wasps, we made a literature search of potential mortality factors of individuals and colonies. Although the role of parasitism cannot be ruled out, we highlight the potential of vole cyclicity in explaining the migrations. Because the spatial scale of vole-cycle asynchrony is located at the same level (γ scale) as the range of migratory movements, spring flights could rid bumblebees and wasps of strong nest-site competition among colony-founding queens, and of severe predation by voles in high vole-density regions, to take advantage of abundant, empty vole burrows as nest sites in low-predation, relatively vole-free areas. As a corollary of the migratory movements, relaxed parasite pressure is expected.