Build it and they will come.

Baseball's “Field of Dreams?”

No, a bee nesting block.  Think "bee condo."

It's an artificial nesting site made of wood and drilled with different-sized holes and depths to accommodate the diversity of native pollinators. Often the bee block is nailed to a fence post. Native bees, such as leafminer bees and blue orchard bees, build their nests inside the holes.

Fact is, North America is home to about 4,000 species of native bees. (The  common honey bee is not a native; colonists brought it here from Europe in the 1600s.)

Members of the Xerces Society, an international organization "dedicated to protecting biological diversity through invertebrate conservation," are keen on protecting the habitat of native bees and other native invertebrates. As part of their public outreach program, they publish books, pamphlets and fact sheets. These include  Pollinator Conservation Handbook, Farming for Bees, and the fact sheet, Bumble Bees in Decline.

As for the bee condos, thousands are sold each year in the United States, according to entomologist Mace Vaughan, pollinator program director of the Xerces Society, based in Portland, Ore. As concern for the environment grows, more and more farmers and urban gardeners want to attract and accommodate the native bees. Native bees are important crop pollinators, Vaughan says, and the work people do on behalf of the pollinators also supports other beneficial insects and wildlife.

Vaughan, who escorted a group of us on a recent Yolo County farm tour, said many of our native bee species are much more efficient than honey bees at pollinating some crops.

"For example, only 250 female orchard mason bees (genus Osmia, also called blue orchard bees) are required to effectively pollinate an acre of apples, a task that would require 1.5 to 2 honey bee hives--approximatley 15,000 to 20,000 foragers." (Source: Farming for Bees, a Xerces Society publication.)

Native bees sport such names as miner, carpenter, leafcutter, mason, plasterer or carder, reflecting their nesting behaviors.

See the bee (below) heading toward the bee block? Xerces Society member Robbin Thorp, emeritus professor of entomology at UC Davis who researches native pollinators, including bumble bees, says this is a female leafcutting bee, "probably the introduced Megachile apicalis, a specialist on Centaurea species, especially yellow starthistle."

The leafcutter bee, as its name implies, cuts leaves to form its nest.