The Buzz About Bee Houses for Your Garden

With so many species of solitary bees in North America, chances are good that you can attract these pollinators to your yard

08-01-2002 // Cynthia Berger

AT FIRST GLANCE, Taren Urquhart's backyard in suburban Vancouver, British Columbia, looks like a condo for birds. Little wooden houses with quaint, peaked roofs are everywhere--on the deck railing, under the eaves, near the barbecue. But these houses are for bees, not birds. Urquhart first started luring them to her yard about three years ago after learning--at a local apple festival--that bees make good pollinators.

Her tenants are blue orchard bees (Osmia lignaria), one of 4,000 native U.S. species that scientists classify as "solitary bees." Unlike the more familiar honeybees--imported from Europe--which tend to defend their nests aggressively, these widespread bees have no hive to defend. "This makes it easy to share your turf with them," says Urquhart, an amateur entomologist who makes and sells bee houses and lectures garden clubs and schoolchildren about the benefits of bees. Each female nests alone, and if her nest is attacked by a predator, such as a woodpecker, she doesn't waste time on defense but simply finds a new location or fixes what has been destroyed. "They sting only under extreme duress, say, if you picked one up and squeezed it--hard. And even then it's no worse than a mosquito bite," Urquhart adds.

Blue orchard bees are different from honeybees in other ways. With their metallic blue bodies and transparent wings, they look more like jumbo houseflies. And they are hardy; they're not susceptible to killer parasites, such as varroa and tracheal mites, which have decimated North American honeybee populations in recent years.

More to the point, orchard bees are better pollinators. They work faster than honeybees and do a better job spreading pollen around. And while honeybees hole up in their hives on cold or rainy days, orchard bees willingly work in bad weather.

"Encouraging solitary bees is a good idea for anyone who has fruit trees or berry bushes in their garden," says Idaho entomologist Karen Strickler. Apple blossoms, pear and peach blooms, and the flowers on raspberry bushes and strawberry plants must be pollinated to produce fruit. "If you have garden crops such as squash, tomatoes and peppers--which are actually fruits that come from flowers--they need pollinators too," Strickler adds.

With so many species of solitary bees in North America, chances are good that you can attract them to your yard. And when you do, the bees will benefit, says Matthew Shepherd, director of the pollinator program for the Xerces Society in Portland, Oregon.

"Admittedly, scientists haven't done much research to find out which bees live where or whether populations are in trouble," he says. "But we do know that some species are specialists, so they're less able to cope with changes in habitat, for example, as suburban development replaces fields and woodlots. That means anything you do to enhance your backyard will likely help bees, even if we can't point to particular species that will benefit."

One way to give the bees a boost is to provide nest sites, popularly known as bee houses. Solitary bees can't excavate their own holes, and their natural nest sites--woodpecker holes, hollow tips of broken tree branches and tiny tunnels made by wood-boring beetles, for example--are not exactly abundant. So the insects readily accept substitutes. "I've heard of bees nesting in wind chimes, bamboo blinds, even a teapot spout," says Urquhart. "One man told me he had a bee fly through an open window and build a nest in his headphones! That's how desperate for habitat these bees are."

"Bee houses are really simple to make," says Shepherd. All you need is a piece of untreated 4 x 6 inch or 6 x 6 inch lumber. Or just use a good-sized dead tree limb or chunk of firewood. Cut the wood into 8-inch-long blocks. Then, using a 5/16-inch bit, drill several rows of holes about 6 inches deep in each block. (Be careful not to drill all the way through the wood as bees prefer dark tunnels.)

Space the holes at least three-quarters of an inch apart, but don't worry about making neat rows. "The bees don't care," Shepherd says. Drill slowly and across the grain, so the holes have a smooth interior; bees will avoid holes that feel rough. For a finishing touch, add an overhanging roof to shed storm water and provide protection from the afternoon sun.

Hang your bee houses in a sheltered place, at least three feet off the ground, with the holes facing south or east to catch the morning sun. "Our bee houses are mounted six feet up the side of our shed," says Linda Warren, a master gardener in Marinette, Wisconsin, whose backyard contains a variety of fruit trees. "The bees seem to prefer it there; I think when you hang houses in a tree, it's too shady."

Ideally, you should put your bee houses up in early spring, before the bees are active. "I put some up in my yard last year, and the holes were occupied within two or three weeks," Shepherd says. "Pretty instant results! And though I admit I'm a bug geek, bees are really fascinating to watch."

Adult blue orchard bees emerge from their cocoons in early spring, right around the time most flowering trees burst into bloom. After a frenzy of mating, the males die and the females get to work locating suitable nest sites and ferrying loads of pollen and nectar inside the nesting holes. It takes 15 to 20 trips to provision one "cell" in a nest. The female mixes pollen and nectar together to form "bee bread," then she lays a single egg in the nourishing mixture. Finally, she gathers a bit of mud and builds a little wall to seal the cell. She repeats the process--gathering pollen, laying an egg, sealing the cell--until the tunnel is filled with five to ten cells. Then she caps the nest with more mud and flies off to find a new nest site.

Blue orchard bees are active only for about four to six weeks in spring. But other species of native solitary bees use similar nest sites, so you can provide for pollinators all summer long by offering nesting holes in a variety of diameters. "I tell people to just go crazy with their drill bits," says Urquhart. "You'll be amazed at what you attract." After the blue orchard bees finish nesting, leafcutter bees, which seal their nest cells with chewed-up leaves instead of mud, get busy. Also active later in the summer are solitary wasps. Even though they're not pollinators, wasps are handy to have around because they prey on garden pests such as aphids and caterpillars.

Besides offering nesting sites, you can also make native bees feel at home in your yard by digging up a bit of bare ground and keeping it damp; orchard bees need mud to partition the cells in their nests. Another idea is to mix up a pie-plate full of mud and leave it conveniently close to blooming flowers.

The best bee habitat offers a succession of blooms all summer long. "We started by surveying our property once a week in spring to see what plants we had and when they bloomed," says Warren. "Then we supplemented with other species." Bees don't see the color red but are attracted to blue, violet, white and yellow. Virtual bee magnets include strawberries, raspberries, blackberries, roses, clovers, mustards, wild mints and wild geraniums, plus early-flowering trees such as wild cherries and willows (from these groups, chose the species native to your region). Avoid fancy hybrids--they're showy but produce little or no pollen.

"When you're working on conservation efforts for charismatic megafauna,' such as wolves or eagles, it takes thousands of dollars' worth of equipment and years of training to make a difference," Shepherd says. "But conserving habitat for native pollinators is easy, and doing just a little in your own backyard can make a big difference."

For more on building bee houses, visit the U.S. Department of Agriculture at www.loganbeelab.usu.edu . Cynthia Berger wrote about  attracting dragonflies to your yard in the April/May 2002 issue of National Wildlife.

Find out how you can turn your garden into a Certified Wildlife Habitat.

Related Reading
Few people realize that native bees are crucial to the ecology and the economy of the United States. To learn more about these important plant pollinators, see "Waxing Eloquent on Native Bees" (National Wildlife, April/May 2001).

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