Friday, March 26, 2010

Bumblebees and Climate Change

Bumblebees can now be spotted all year round in southern England (Read more here).

Yes, British Winters are still cold, but not as cold apparently, as they used to be. Bumblebees are hardy anyway, and can continue to fly in search of food at colder temperatures than most other pollinators. Besides, in British gardens there are apparently some cultivated plants that bloom during the Winter months, so the bee food supply is continuous.

Right: The Buff-tailed Bumblebee, a British species seen in very early Spring.

Bumblebees in temperate climates usually escape winter as part of their annual colony life cycle. Normally it is only the fertilized queen that overwinters. In the Fall, she chooses a sheltered spot, often in a shallow burrow in the soil. There she waits until winter has passed and Spring flowers promise a fresh supply of nectar and pollen.

The queen begins a new colony first by finding an abandoned mouse nest or other suitable cavity, often underground. She gathers nectar and pollen to nourish the larvae that develop from the eggs she lays. When her first brood of worker bees emerge as adults, they take over the job of gathering food, leaving the queen to the tasks of laying eggs and maintaining order in the colony.

By mid- to late-Summer, the bumblebee colony starts to produce sexually active males and queens. When these new queens have mated, they are the ones who normally overwinter and begin the next generation. The old queen and the remaining workers and drones usually die when they can no longer find enough food and the first heavy frosts overtake them.

These observations of Winter-active bumblebees in southern England raise some intriguing questions. Are they mated queens that just don't bother to hibernate? Or are they workers and males left over from the previous summer who can still find enough food to survive? If the latter, do last year's workers and males become competitors with the new queens for scarce Spring food resources?

Dave Goulson's observations suggest that mated queens of Bombus terrestris in southern England just go ahead and found a new nest, not bothering to hibernate first. But if they were to start simply laying eggs in their maternal colony, this would seem to put the species well on the way towards continuous, immortal colonies, like those of honey bees.

As with all of the many changes that have occurred in Earth's environment during past millenia, those bumblebees that can adapt gracefully will survive and prosper. Those that cannot adapt will become just another chapter in bumblebee history.

[Photo of B. terrestris from the Wikimedia Commons, CC License]

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