Mason bees are a delight in the garden. They're incredibly industrious, providing hours of entertainment as they endlessly gather pollen and fill their nests. And they're non-aggressive; they don't swarm in alarm or even sting much. The male is harmless, and the female may deliver a very mild sting, similar to a mosquito bite, if she feels her life is threatened.
Adding Mason bee houses to your garden will be a treat for you and your pollination-hungry plants.