How do I know if the bees are nesting?

A sign of bees nesting in your bee house is evidence of natural nest-building material like mud, pollen or leaf bits. You can use a flashlight and peek at the nesting holes to look for bee faces or bee rears. It can sometimes be hard to see a small bee who is resting in the very back of the nesting hole. Female bees sleep in the nesting holes overnight.