For worker bees, seeing is believing. Queen bumblebees have pheromones, a mixture of chemicals that affect another bumble bee's behavior. When worker bees sense these chemicals, they become infertile, but this trick only works if they can see the queen. 

Scientists tested this mysterious need for visuals by playing different scenarios. First, they had their control, meaning business as usual. Workers could sense the queen's pheromones and see her and see babies, so they remained infertile. 

If the worker bees saw the queen without her babies, they were still infertile. But when they said goodbye to the queen and just kept the babies in view, the worker bees started getting ready for fertilization. 

And while we don't know exactly how yet, that's something that only happens when the queen isn't around. So for these worker bees, out of sight and smell, out of mind.