How the bumblebee survives in cold weather

David Chapman / 02 August 2012

David Chapman explains how bumblebees manage to survive in air temperatures that are too low for them to fly



We have lots of different types of bees in the UK and some of them will visit our gardens to feed. Bumblebees are a specific group of bees which are mostly large, very hairy and sociable creatures. There are more than 250 species of bumblebee in the world, of which we have about 24 species in Britain and probably only six of these are regular garden visitors.

Although many bumblebees have common names these are often unreliable because some species have many different common names so scientists exclusively use scientific names for them.  The word 'bumble' can mean to blunder around in a haphazard fashion which seems well-suited to the bumblebee but it can also mean 'to make a buzzing or humming sound' which is more likely to be the reason for the bumblebee's name.  Interestingly, the buzz of the bumblebee is actually created by the vibration of its muscles rather than the flapping of its wings.

It is interesting that bumblebees can survive in air temperatures which are much too low for them to fly. Their muscle temperature needs to be 30°C before they can take flight and yet ambient temperatures in Britain rarely exceed 20°C.  In order to warm up they shiver their flight muscles, a bit like we might shiver when we are cold, but the clever thing is that they can uncouple their muscles from their wings so despite shivering their flight muscles their wings don't move.  Once up to temperature their large, hairy bodies help them to retain the heat.

Bumblebees are regarded as social because they make annual colonies which follow a typical annual cycle. In spring, the queen's first batch of eggs produces female workers whose task it is to increase the colony size.  Towards the end of the summer she produces a batch of male workers and queens, these mate and the fertilised queens survive until the following year to start the cycle again.  All this takes place in their nest, which often comprises a ball of grass and moss filled with wax cells, they can be underground, in various holes, or on sunny banks. 

Their larvae are fed on nectar and pollen which the adult workers collect from flowers. They gather pollen on specially adapted hairy back legs in what are known as 'pollen baskets'.  To carry the nectar they drink it from the flower and store it in a 'honey stomach', inside their abdomen.  Their stomachs can hold up to 0.2 ml of nectar and they need to visit about 60 flowers to reach this capacity.

If you have found any bumblebee nests, or if you have been able to photograph any bumblebees with a digital camera, then the Bumblebee Conservation Trust would love to hear from you. They are monitoring the populations of bumblebees across the UK in an attempt to understand them better and ultimately protect them. See their website at www.bumblebeeconservation.org.  This website also has an excellent section on gardening for bees.

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