The Buff-tailed Bumblebee (Bombus terrestris) is such a familiar sight in gardens, parks and the countryside throughout the UK and Europe. A hardy species, the large queens (up to 3cm) can emerge on sunny days in the middle of winter; their flight muscles can operate in temperatures as low as 5 degrees celsius. Queens will emerge in around March, as the air warms and spring flowers are peaking. 
You will see them sunbathing, and though they aren't moving, don't worry, they are busy getting themselves warmed up and flight-ready. Sometimes you will see small, pale mites clinging onto them - these are harmless and are just hitching a ride between nests, where they eat detritus. T
he queen finds a nest site and construct several conjoined nest cells, in each one laying a single egg and provisioning with pollen. Bumblebee queens can genetically control the sex of their young; and so these early offspring are always workers. As the first workers emerge, they will take over nest-cell building and foraging duties, leaving the queen to focus on egg-laying, producing queens. The in early summer, the queen flicks her genetic switch and begins laying male eggs. The new queens emerge with the males, fuel up on nectar and go into hibernation in around August, in a shallow hole in the soil, or other snug nook. There they stay until the following spring (apart from the occasional cold-weather sojourn), when they will emerge to repeat the cycle. There does appear to be increasing evidence of winter activity in Buff-tails.There are even records of winter-active nests, as our winters become milder.
© Gail Ashton. February 2022
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