I love watching Bees do this. If theres a bee not moving very much then it's likely out of energy. I learnt on QI once that if you put a blob of honey in front of them they eat some and it gives them enough energy to fly home. I've tried it a few times and funny enough it does exactly that. Watching their little tongues lick it up fascinates me. Here are some pictures of it.
This one shows their head, I think it looks like they have one of those black dome cctv cameras on their head, that idea could be taken further.