Spring is the time for hope and for creating new life. But Spring can be the most dangerous period of the year for bumblebees.
We'll be seeing bumblebees on the wing soon (our colleagues in England are seeing them already), for Spring is when mated queens emerge from hibernation. Each has overwintered in a shallow burrow in the soil. Energized by the warming rays of the sun, each queen must crawl to the surface and fly off in search of a first meal of nectar to fuel the colony founding tasks that lie ahead.
But what if an unusually cold winter or Spring rains that flood the soil kill off most of the hibernators? What if there are no blossoms to forage after they emerge? What if too many queens have survived and there is not enough nectar to go around?
An uncertain environment and intense competition make each new Spring a challenge. This is why early bumblebee populations may be boom or bust - tens of thousands of queens in some years, few in others.
One strategy that bumblebees appear to have evolved in order to reduce competition for resources each Spring is staggering emergence times. North American bumblebees (like those in any temperate climate) can be characterized as either early-Spring, mid-Spring or late-Spring emergers.
Right: Emergence pattern for 3 common eastern North American bumblebee queens.
Because most wildflowers bloom at different times through the season, early emerging queens have access to a different initial food supply than those emerging later on. The result - more bumblebee species can co-exist in the same community than if they competed head on for every resource.