This piece with photos was submitted in June 2009 and accepted for publication by Mother Earth News for the Country Lore column
With the demise of honeybees, native mason bees have taken up the pollination banner. They look like small blue-black flies that rarely sting. Particularly useful in fruit tree orchards, mason bees (also called blue orchard bees) can visit hundreds of flowers per day. They don't make honey, but they collect pollen for nest holes where they lay eggs and then plug the holes with mud. A female can lay up to 35 eggs in her lifetime. The bee larvae and cocoons spend winter in the holes, then hatch in the spring about the same time as the fruit trees blossom. Mason bees live about two months, generally staying within a radius of about 100 yards of where they hatched. In the wild, mason bees use holes in tree bark, fence posts, construction wood, or any other opening a little bigger than their bodies for their nests. Before we put up a nesting block, every year they managed to sneak into our garage and fill several of the holes in the shelving pegboards.
Although nesting blocks can be purchased commercially from garden supply companies (so can the bees), it's easy to make your own. Use thick planks of untreated lumber, ideally placed near the orchard trees that you need pollinated. From our experience, the bees prefer deep 1/4-inch holes (we tried 1/4, 5/16 and 3/8 at different depths). Because mason bees lay female eggs toward the back of the hole and male eggs toward the front, some suggest holes that are too shallow result in mostly male bees. Commercial nest blocks use straws in nesting holes, but we found that the bees wouldn't use them here.
Once you get your nesting block up, watching
the bees fill the holes with eggs, pollen and mud is great entertainment!