|Mason bee houses installed into the garden shed gable. Note the boxes of bees sitting on top. They go out to pollinate and then come back to lay their eggs in the tunnels, sealing off the openings when filled.
Mason bees are like flying salmon. You simply place the boxes of eggs next to the houses of tunnels and once they hatch, they fly out, do their thing then come back to the same place to lay the next generation. Each box of bees contained the eggs of 8 females and 4 males. Since we were late getting the boxes out, it didn't take long for them to bust out. It's a temperature thing. Hopefully, the holes will fill. The females control the sex of their prodigy. As in much of the animal world, the males are expendable, so their eggs get laid in the front part of the tunnel, lest they get devoured by another critter that finds them tasty. In the fall, we'll break apart the houses and store the eggs in the refrigerator for the next season. If you don't harvest the eggs, they can get attacked by mites. In early spring, the eggs go back out next to the cleaned (and sanitized!) houses for the next go around. Since the bees are the first pollinators, it's important to get them out when the fruit trees are blooming. They can handle colder weather than other bees, so are out before the other bees appear.
Mason bees aren't aggressive, so are easy to work with. In fact, it's just a matter of letting them do their thing. With the proper habitat and happy bees, it's possible to get enough bees over time to share with others. With colony collapse disorder destroying bee populations, mason bee populations need to be encouraged.
Now to finish that green roof!