I've been interested in Mason Bees (Osmia lignaria) since reading an article about them in a University of Arizona publication last fall. Until I read the article, I didn't know a thing about them, or that they occur naturally in Arizona as well as throughout the United States. These bees are smaller than honey bees and almost black in color. They are docile and friendly, and do not normally bother humans if they are not bothered. They are not destructive like carpenter bees because they do not excavate nest holes for themselves. The way to attract them is to provide them a bee house all ready for nesting. The nests are placed facing east or south. In Arizona, the bee house can go up from February to July to attract the bees.
Supplying a ready-made nest helps the female Mason bee spend less time and effort on nest preparation and more time on gathering nectar and pollen and laying eggs. First, she places a mud plug at the bottom of the tube, then brings 15 to 20 loads of nectar and pollen from spring flowers until she has enough to begin laying an egg in the tube. Then, she will plaster the opening of the tube with a mud plug, and move on to prepare and complete the next tube and so on. She only lives for about a month, and will produce one or two eggs a day. The eggs become larva, which feed on the pollen pellet. After it consumes the pellet, it spins a cocoon and pupates within the tube cell. Around September, the larva transforms into an adult bee that stays in the plugged tube until the following spring. And the cycle begins again.
So far, no Mason bees have nested in my bee house. I wonder if I got it up too late in the season, or if there are no Mason bees around here yet. I guess I'll just wait to see if any show up between now and July. I hope so, as I was looking forward to watching them at work.
Honey bees aren't interested in the nests, but some leaf cutter bees and wasps will build nests in the bee house, so I'll have to watch for that. You can tell if something other than a Mason bee has filled a tube. The Mason bee plugs have a rough mud surface, the wasp mud plugs are smooth, and the leaf cutters seal their tubes with chewed leaves so they are green in color.