Bumblebees are familiar and charismatic insects, occurring throughout much of the world. They are increasingly being used as a model organism for studying a wide range of ecological and behavioural concepts, such as social organization, optimal foraging theories, host-parasite interactions, and pollination. Recently they have become a focus for conservationists due to mounting evidence of range contractions and catastrophic extinctions with some species disappearing from entire continents (e.g. in North America). Only by improving our understanding of their ecology can we devise sensible...