> the winter cluster causing the bees to not be able to generate enough heat with wings.
* Honey bees do not generate heat with their wings.
> It is clear that metabolic rate (MR) and visible activity can be independent. A high MR can be achieved by rapid vibration of the thoracic muscles which is not visible externally.
> the muscle responds with a small twitch of 2 to 3 ยต in excess of the state of contraction characteristic of this stimulation level. Along with the contraction one observes a considerable heat production.
> individual bees gain heat through rapid small-amplitude contraction - relaxation cycles of their thoracic wing muscles. During these periods, action potentials from thoracic muscle tissue show trains of impulses of higher frequency than flight frequencies. Heat production results from the low mechanical efficiency of this musculature which makes up the bulk of the thorax, and is among the most metabolically active tissues known.
> Since the indirect wing muscles are the main source of heat and a proper functioning of these muscles is only guaranteed at temperatures higher than 18C (64F) an area must be available to which bees from the outer layers of the cluster can go and take part in social heat production.
SEE
Esch H, Bastian J (1968) Mechanical and electrical activity in the indirect flight muscles of the honey bee. Z Vergl Physiol
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