Bees are important pollinators — that fact can’t be stressed enough. Honey bees, which are native to Europe, Asia, and the Middle East, are used in agricultural areas to pollinate fruit trees, vegetables, and flowers. In some areas, honey bees also suffer from colony collapse disorder, a mysterious condition where the worker bees abandon their queen, colony, and larvae. While a lot of attention is given to the honey bee, native bees can also provide pollination services to farmers and gardeners (although their populations may not be as substantial as those of honey bees).
Many gardeners know the value of these bees, so they set up ample food sources in their yards to draw them in. This is easily done by planting a diversity of flowering shrubs and trees that produce either nectar or pollen in the garden. Like birds, of course, native bees also need a place to nest, lay eggs, and help their young develop.
Unlike honey bees, solitary bees aren't social, don’t have a queen, and don’t live in colonies. Depending on the sex of their offspring, they also may or may not provide their developing larvae with food. The vast majority of backyard bees are solitary (mason, blue orchard, and mining bees, to name but a few). In the U.S., there are over 4,000 species of solitary bees, all of which vary tremendously in size and lifestyle.
Attracting Backyard Bees
Attracting bees to the garden is the easy part. Just walk around it during the summer, and there should already be a few bees buzzing about. Whether they're after nectar or the pollen on your sunflowers, eggplants, and tomatoes, these bees are providing an important service: pollination. Though honey bees are used in orchards to pollinate cherries, apples, apricots, and other fruits, native bees do a much better job pollinating other crops, including cranberries, blueberries, and watermelons.
While food (i.e. nectar and pollen) should be easy enough to provide, gardeners will also want to minimize the use of chemical pesticides in their gardens to help out these pollinators. Places that rely on herbicides and pesticides for insect or mosquito control may see a significant reduction in their bee populations, as these creatures are quite sensitive to chemicals.
Depending on the species, female bees will usually bring leaves and pollen to the nest holes for their larvae. Female mason bees will lay one egg in a cell, which itself will be stocked with pollen and nectar. Each cell is walled off from the others by a plug of mud. The young develop within these cells and emerge as adults the following spring.
Providing Nesting Locations
Native bees all tend to build their nests in different substrates (again, depending on the species). Some nest in hollow plant stems or old logs, while others nest underground. Providing a variety of substrates — just like offering a wide range of nectar and pollen-producing plants — is key to successfully enticing bees to nest in your backyard.
A lot of the kits that are currently on the market essentially consist of a wooden block with holes drilled into it. These nest blocks attract carpenter, mason, and orchard bees. The amount of cleaning up you're willing to do after the nesting season will determine whether or not those holes should be left alone or lined with extractable paper tubes beforehand. Purchasing replacement tubes is the easiest way to prepare a nest site for the next year.
Of course, if you prefer to build your own nest box, there are still many options available to you, ranging from simple to complex.
The simplest thing is to drill holes into a log. These can be about a drill bit in length (four to six inches) and anywhere between 3/32nds and 3/8ths of an inch wide. Randomly drill holes into the log, leaving some space between each one. Naturally, different-sized openings will attract different species. The log or logs can then be stacked or placed in a protected location where they won’t topple over. For instance, you might arrange a number of logs within an open shell (walls, roof, and back) to securely hold them in place. Later on, the outsides of the shell can be painted for a decorative look.
Alternatively, you could use a four inch by four inch block of untreated wood. Don’t use pressure-treated lumber or wood that's been stained. Drill deep holes into the wood, but be careful not to create any “back door” entrances. A simple square of wood (about six by eight inches) can be cut and nailed to the top of the block to create a protective roof. Mount this block in a protected spot and affix it so it doesn’t topple over. Adding a metal ring to the back can be a good way to secure the block to a fence or post. Orient the openings toward the south.
Another design utilizes four to six-inch long sections of cut bamboo, which are stacked horizontally within a cylinder and packed in tightly so there isn’t any movement between shoots. A thin roll of paper, like parchment paper, can then be inserted into each section for easier cleaning at the end of the season. The cylinder will also need to have a back covering so the tubes are open only one one end.
A more complex design involves creating a box with square layers or bamboo sections that are drilled all the way through. A “back door” section of wood is then added to the box, which can be removed at the end of the nesting season to make washing the tubes out easier for you.
Ground Nesting Bees
For ground nesting varieties like digger and mining bees, you'll want to section off a dry patch of land away from any irrigation systems. Next, you can either mound up the soil or work in some additional sand to create an easy substrate for the bees to excavate. Remember to pick an area that dogs, kids, and other people won't be walking over.
Nesting Box Placement
Secure the box to a fence, post, or tree approximately three to five feet above the ground with a south or southeast orientation. The box or tube will be up for the majority of the winter, so be sure to put it in a safe location. Keep the box away from of any irrigation spray, and make sure that the entrance is visible from the house so you can watch your new residents move into the garden.
Many local extension services offer plans or suggestions for adding bee boxes to the garden. The Xerces Society, located in Oregon, is an excellent organization with a highly informative website on bees and other insects.
The BugGuide is another great place to learn about bees.