Drone cells

Timothy the beekeeper was here yesterday to have a look at the hives again. There was a southwesterly gale blowing and the bees were pretty upset. I put on the bee suit to be on the safe side. Indeed the bees were not amused when the hive was openend and they massed around me. The weather has had a negative impact on them. Nevertheless I could see real growth when the lid went off. On this picture the drone cells are clearly visible on the frame. They are the yellow balls. According to Timothy that is a seasonal feature. How he knows that those balls have future Drones inside and not worker bees, I'm sorry to say I didn't ask.