Red Mason Bees are the most likely bees to use these houses. They can be seen from April to July. There are about 70 types of solitary bees that nest 'aerially' rather than in the ground. A few types of bees have learned to use bee houses like ours.  We may also be lucky and get Leafcutter Bees, Orange Vented Mason Bees, or even Blue Mason Bees.

When they nest, females line hollow tubes with mud and pollen to create individual cells for each egg. She lays one or two female eggs at the back of the tube away from predators, followed by male eggs.  She may do 15 trips for pollen and even more in search of mud. The females have about 40 eggs, so they may fill several tubes.