Mason bees use mud to pack the holes where they lay their offspring. They go to the back of the hole in the nesting block and place a ball of pollen and nectar that we call “bee bread.” They lay their egg on top of the food source, and then build a small mud wall, creating a small cell. They will repeat this process until they have reached the front of the hole, and then plug it with a ¼” of mud that they carry with their mouths. At the end of the springtime, in each hole of the nesting block there will be between 5-10 mason bee offspring behind a plug of mud. When you host mason bees in your yard, you will need to make sure that you mud hole stays wet throughout the season.