Here are a few interesting facts about the leaf cutter bee. It cuts circles or ovals from leaves and uses them to build nest cells. It then fills the cells with pollen and nectar, lays the eggs and then closes the cell with another leaf. It is a non-aggressive bee with just a mild sting. Rather than being a part of a colony, the leaf cutter is a solitary bee.
I'm really glad that it isn't aggressive since it is obviously nesting in the patio wall.