If you didn't see the BBC programme this week 'Richard Hammond's Invisible Worlds', then you might still be able see it on the BBC iPlayer (more here too). It was very interesting as it brought up two new facts for me. One was that there are special bees in each colony that are 'heater' bees which help keep the brood warm. They have to be fed extra food as they burn so much energy. They were picked up with thermal cameras and there is great footage in the programme; here is a screen shot that shows two of these heater bees amongst the other bees in the colony.