How do bumblebees hibernate?

Bumblebees are the sound of summer, and you won’t find many flying in the winter months, except the occasional nest in the warmer parts of the country. But just where do they go?

Before answering that question, here is a quick recap of the bumblebee life cycle: bumblebee queens emerge in spring and establish nests in various places. The queen bee lays several broods of worker bees through the spring and summer, and eventually she will begin to produce new queens and/or male bees. The new queens and males leave the nest to mate with bees from other nests, and the new queens go into hibernation, while all of the old queens, workers and males die. The newly mated queens will then use the sperm from the male to fertilise her eggs the following year, and the life cycle begins again.

Hibernation can take up a large amount of a bumblebee’s life, and some queen bees can hibernate for nine months – almost three quarters of their life! Going into hibernation is important because it protects the queens from the rigours of life above ground, with the risk of predation, starvation and diseases.

To hibernate, queen bees dig into well-drained soil, usually on north-facing banks. This varies between species but it’s thought that they choose north-facing banks because if they were south-facing, they would be exposed to the low winter sun which could heat the soil and bring the bees out of hibernation before spring arrives. Staying in banks probably helps them avoid being flooded, as does the well-drained soil. They dig down about 10cm or more, and excavate a little hole in which they will spend the winter, surviving temperatures down to minus 19C!

Last month I walked up Schiehallion, a mountain in the Highlands of Scotland. There I was lucky to see dozens of Blaeberry bumblebee (Bombus monticola) queens flying, and many were trying to find hibernation spots. I even found one at the summit – over 1,000m above ground! Here is a video I took one of the bees trying to dig into the soil. Hopefully she’s safely tucked up now!

 

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