HONEYBEES keep warm during chilly winter months by huddling together in a ball. Now it seems this central-heating system has a mysterious thermostat.
Anton Stabentheiner and his team at the University of Graz in Austria took infrared images of a cross section through a winter ball. When bees on the outside of the colony got too cold, those in the centre heated up – presumably by contracting flight muscles – so that their warmth would radiate out (Journal of Experimental Biology, vol 206, p 353). But how the call for extra warmth makes its way to the centre is unsolved.