The following is an excerpt from the Xerces Society of Invertebrate Conservation. This fact sheet gives information on how to provide nest sites for native bees, including nest blocks and bare ground for solitary-nesting bees. For more info go to http://www.xerces.org.
Pollinators are a diverse and fascinating group of animals. In addition to their beauty, pollinators provide an important link in our environment by moving pollen between flowers and ensuring the growth of seeds and fruits. The work of pollinators touches our lives every day through the food we eat. Even our seasons are marked by their work: the bloom of springtime meadows, summer berry picking, and pumpkins in the fall.
There are 4,000 species of native bees in North America. Together they form the most important group of pollinators. Like all wildlife they are affected by changes in our landscapes, especially the loss of nesting sites. Bees make nests in which they create and provision brood cells for their offspring. In many modern landscapes, a desire for neatness has usually resulted in the removal of bare ground, dead trees, and untidy corners of rough grass—all important nesting sites for bees.
Wood Nesting and Cavity Nesting Bees.
About 30 percent of our native bee species make their nests in old beetle tunnels in snags or similar locations. The female bee builds dividing walls across the tunnel to make a line of brood cells. Where you can, retain snags. Where you can’t, make some nesting blocks. (Alternatively, many garden centers and back yard bird shops sell them.
Bee blocks can be made by drilling nesting holes between 3/32” and 3/8” in diameter, at approximate 3/4” centers, into the side of a block of preservative-free lumber. The holes should be smooth inside, and closed at one end. The height of the nest is not critical—8” or more is good—but the depth of the holes is. Holes less than 1/4” diameter should be 3-4” deep. For holes 1/4” or larger, a 5-6” depth is best.
Logs and Snags
Get some logs or old stumps and place them in sunny areas. Those with beetle tunnels are ideal.
Plant a few upright, like dead trees, to ensure some deadwood habitat stays dry. On the southeast side of each log, drill a range of holes, as outlined above.
Stem or Tube Bundles. Some plants, like teasel, bamboo, and reeds, have naturally hollow stems. Cut the stems into 6” to 8” lengths. Be careful to cut the stems close to a stem node to create a tube with one end closed. Fifteen to twenty stem pieces tied into a bundle (with the closed ends of the stems together) makes a fine nest. Or, make a wooden frame to hold as many stems as you like. Paper tubes can be used as well. Just make sure they stay dry.
Location of the nesting sites is important. These nests should be placed where they are sheltered from the worst of the weather, with entrance holes facing towards east or southeast, so they get the morning sun. With stem bundles, be sure that the stems are horizontal. The nests can be any height from the ground, but between three and six feet is convenient.
Put them on a building, fence, or stake, or place them in a tree. Fix them firmly so they don’t shake in the wind.
Most native bees—about 70 percent of species—nest in the ground, and need access to the soil surface to dig their nest. Each female excavates her own nest tunnel and brood cells, and stocks the cells with nectar and pollen. Where possible, keep bare or partially vegetated ground. Where you can, create more.
Ground Nesting Bees
Bare Ground. Simply clear the vegetation from small patches of level or sloping ground and gently compact the soil surface. These patches can be from a few inches to a few feet across, but should be well drained, and in an open, sunny place. A south-facing slope can be a good location. Different ground conditions—from vertical banks to flat ground—will draw different bee species, so create nesting patches in different areas if you can to maximize the nesting opportunitites.
Sand Pits and Piles. In a sunny, well-drained spot, dig a pit about 2’ deep, and fill it with a mixture of pale-colored, fine-grained sand and loam. Where soils do not drain well, a pile of the sand/loam mixture can help, or make a raised bed. If space is limited, you can fill planter boxes with the sand/loam mix.
We’re happy for you to copy this fact sheet or to use this text elsewhere, as our aim is to get the information spread far and wide! Please just credit The Xerces Society whenever the text is used in another format. The photograph, however, is copyrighted and may not be used in any way except in this fact sheet. If you are interested in photos of bees, please contact us.