Don’t invite native bees to your yard just to be virtuous. Do it because they will pump up your garden’s produce production.
“See that?” asks Gordon Frankie, an entomologist and professor at the University of California-Berkeley. We’re standing in his bee garden, a long, narrow rectangle planted with patches of different wildflowers and shrubs at the edge of a field surrounded by city buildings a block from the main campus. He points to a fat, fuzzy female bumblebee turning in tight circles in the center of an orange California poppy blossom.
The bee, comically large for the flower, crawls around and around the stamens, brushing off golden pollen grains, which she packs into baskets of stiff hairs on her hind legs. She is gathering the fat- and protein-rich pollen for food, explains Frankie, deeply tanned and clad in a blue Hawaiian shirt, shorts, and sandals. “There’s a group called Halictids [sweat bees] that go in these flowers on sunny days and roll around on their backs and pull pollen down.”
Another bee zips by. “See that?” Frankie says excitedly, again. And he’s off down the path in pursuit. What has him buzzing are the native bees. These little-known, often misunderstood insects are vital to North America’s ecosystems. Our 4,000 species—new ones are still being discovered—are key pollinators for most native flowering plants and many crop plants as well, including tomatoes, fruit and nut trees, squashes, melons, and blueberries. Unlike Africanized bees, native bees are easy to get along with—they rarely sting.
And they’re in trouble. The research that has been done thus far seems to indicate that populations of some of these critical pollinators are declining worldwide due to habitat loss and pesticide use, as well as to climate change, competition with introduced species including honeybees, and imported diseases. The good news, Frankie says, is that gardeners can help: “A plot [of bee-friendly plants] as small as 10 feet by 10 feet can provide significant habitat.” Bees return the favor by pollinating your flowers, thus increasing seed and fruit production—and often stimulating the plant to blossom more abundantly.
I’ve experienced this bee boom in my own high-altitude Colorado garden. After Rocky Mountain beeplant, a wildflower whose spikes of pink blossoms attract clouds of bumble and other native bees, sprouted among my tomatoes, the plants fruited so abundantly that I harvested about 100 pounds of tomatoes from just eight plants. (Commercial tomato growers prize bumblebees for their “sonication,” high-speed abdominal vibrations in the range of middle C that liberate streams of pollen from the anthers of these difficult-to-pollinate flowers, resulting in dramatically higher fruit yields.)
The idea of gardening for native bees grew out of the brand-new field of urban bee research. Frankie had built a career studying bees in wild landscapes when, in 1998, a colleague brought him six species collected from a park in nearby Albany. Frankie was so surprised that city habitat could support native bees that he immediately visited the park—and found nine more species.
He and his students began a bee census in and around the University of California. Their results—82 species in the decidedly altered habitat of the city of Berkeley alone—astonished other biologists. Frankie began to wonder if native bee populations in adjacent wild areas were being sustained in part by the fragments of habitat in parks, community gardens, and yards.
To test that idea he and his students commandeered a scarce slice of campus real estate in 2003 for what is probably the first North American garden devoted to attracting native bees. They planted species and varieties they knew native bees frequented in area gardens, clustering single types in large patches so that bees could see or smell the flowers from a distance.
Frankie recalls the attraction was immediate. “When we were carrying in the plants, bees followed us across the field, streaming in after their preferred flowers.”
Spring bee favorites in Frankie’s campus garden include the brilliant orange cups of California poppy; pink clarkia, with its three-lobed petals; the fiddle-neck-shaped flower clusters of phacelias; and sweetly carrion-scented California lilac. In summer bees flock to salvias and other mint-family plants, buckwheat, and composites including the bright shades of cosmos, yellow tickseed, and annual sunflowers. Forty species of native bees have visited Frankie’s garden so far.
Like birds and other wildlife, native bees are fun to watch. They come in a variety of shapes, colors, and sizes, and can be identified by characteristic flight patterns and behaviors. There are hoverers, darters, and soarers, big bees that bumble about like tipsy revelers as well as tiny ones whose wings shimmer in constant motion. A few are found only on a single species of flower; most are generalists. Some guard floral territories with the pugnacity of hummingbirds, and others forage unobtrusively.
Native bees generally dress in basic black with yellow, orange, red, or pearly stripes, though sweat bees dazzle in metallic greens and blues. They range from nearly two-inch-long carpenter bees, the B-52 bombers of the bee world, to tiny Perdita bees not much bigger than the commas in this story.
Most are solitary. That is, a bee mom constructs and provisions individual nest chambers on her own, digging a nest in the ground, or borrowing or chewing a tunnel in plant pith or wood. She stocks each chamber with “bee bread,” a sticky mix of pollen and nectar, atop which she lays an egg. Then she seals the chamber and repeats the process until all her eggs are laid. Each grublike larva eats until it grows large enough to metamorphose into a winged adult. Then it digs out of the nest chamber to mate and continue the cycle. Solitary bees are generally so busy collecting nectar and pollen that they tolerate human observers up close.
Native bumblebees and sweat bees are colonial, living in extended-family groups of tens to hundreds. The queen or queens lay the eggs, and sterile daughters find food and raise the young. A special generation of males and fertile females—future queens—are born in late summer before the parent colony dies. Unlike nonnative honeybees or Africanized bees, these colonial species are mild-mannered neighbors and their colonies are short-lived.
Other native bee species are parasitic. Cuckoo bees lay their eggs in solitary bee brood chambers. Their larva kills the host’s larva and eats its food. Parasitic social bee queens trick the host colony into raising their own young by either killing the existing queen or hiding in the nest until they smell like they belong.
The diversity of native bees in Berkeley doesn’t surprise John Ascher, a bee researcher at the American Museum of Natural History in New York City, who has tallied 209 species, including 12 exotics, within the city’s five boroughs.
Central Park’s bees include large, shiny black Xylocopa (carpenter bees) that have bored nest tunnels above a ledge on the museum where Pale Male, one of the park’s celebrated pair of red-tailed hawks, often perches. Ascher says he and his colleagues have watched squash bees work Harlem community gardens and bumblebees and sweat bees visiting balcony gardens 21 stories up.
Ascher advises city gardeners to grow plants native to the region instead of exotics, which will attract exotic bees. The plant-it-and-they-will-come scenario, Ascher points out, is true for city bees as well. Squash bees moved into New York City along with squash plants in community gardens. Natives such as blueberry bees, now considered rare in the city, would become more common if gardeners planted the bees’ favored plants—in this case, blueberry bushes.
On average, one out of every four mouthfuls we eat or drink comes from plants that benefit from the services of a pollinator, says biologist Matthew Shepherd of the Xerces Society’s Pollinator Conservation Campaign. Bees provide pollination services valued at $20 billion annually for the nation’s fruit and vegetable crops, along with alfalfa, which feeds the cows that produce our milk and beef.
Nonnative honeybee colonies are still the dominant agricultural pollinators, and farmers still truck honeybee colonies from coast to coast for crops. As exotic mites have decimated honeybee colonies, however, and biologists have begun to suspect that the populous and long-lived colonies can pillage the food supplies of indigenous bees, researchers have searched for native species to take their place in crop pollination.
One success story is the alkali bee, a distinctive species of the Great Basin of Utah, Nevada, southern Idaho, and eastern Oregon that’s marked with opalescent stripes. A single female can pollinate 2,000 alfalfa flowers in one day. Farmers don’t truck in these native bees; they simply excavate “bee beds” in loose, moist, salty soil near their fields, and the gregarious solitary bees arrive on their own. Thousands or millions of female alkali bees digging close-packed nest tunnels create “a shimmering cloud,” says biologist Jim Cane of the U.S. Department of Agriculture’s bee lab in Logan, Utah. Cane estimates the 17 million female alkali bees in just one Washington state valley yielded growers about $6 million worth of alfalfa seeds, enough to plant nearly a million acres of hay.
Cane suggests Great Basin–area bee gardeners plant golden currant, a native shrub with fragrant, bright-yellow tubular flowers, as an early spring nectar source, plus mints such as Agastache or hummingbird mint, thyme, and lavender; and summer-flowering composites like sunflowers, blanketflower, Mexican hat, and goldenrod.
A board member of the Bridgerland Audubon Society, Cane will be depending on native bees to assist in restoring drier upland areas of the chapter’s Amalga Barrens Wetland Sanctuary, a marsh once plowed up and now home to waterbirds, including long-billed curlews and sandhill cranes.
Only bees and a few wasps deliberately visit flowers to gather pollen, making them the single most important group of animal pollinators in the world. In California, says UC-Berkeley’s Frankie, roughly 85 to 95 percent of native flowering plant species depend on bees. (Even plants that don’t rely on pollinators produce more seeds after being visited by bees.)
Without these busy pollinators, ecosystems unravel. Drops in bees correspond with lower plant “birth rates.” Pink ladyslipper flowers in deciduous forests of the Northeast, for example, are visited by native bumblebee species to pollinate their flowers. As the bumblebees decline, the orchids produce fewer seeds and may eventually die out. (Orchid populations are falling, but it’s not yet clear whether it’s due to bumblebee declines.)
Sometimes a bee is entirely dependent on a single plant. In the forbidding Mojave Desert, the tiny Mojave bee collects nectar and pollen only from the endangered dwarf bearclaw poppy. If the poppy disappears, so will the bee.
Biologists agree that habitat destruction and pesticides have hit North American native bee populations hard, but other factors are important as well. Introduced species—including honeybees—outcompete, interbreed with, or kill native bees outright. Exotic diseases and parasites are also taking a toll. Native bumblebees shipped to Europe in the 1990s and bred for the hothouse tomato market returned with a parasite that appears to be responsible for wild bumblebee declines, including two possible extinctions.
Then there’s climate change. At the Rocky Mountain Biological Lab in the high-altitude former mining town of Gothic, Colorado, scientists are seeing bumblebee species move uphill. Bee researcher David Inouye of the University of Maryland, who has spent 37 summers at the remote lab, explains that warming trends and earlier snowmelt have apparently pushed species once restricted to elevations below 7,000 feet up to the Gothic area, at 9,500 feet, and even higher. The result: increased competition among all species and most likely extinction for those that need to live at the highest elevations. (Researchers have already documented local extinctions of other high-elevation species, such as the pika, a hay-gathering rabbit relative.)
Home gardens can’t replace lost habitat for native bees, but they can help. So can habitat-restoration projects on public parks, golf courses, and other urban sites. At a coal-fired power-generating plant in northeast Denver, Audubon Colorado and Xcel Energy are partnering on a multi-year wildscaping project to restore native and wildlife-friendly plants. Company employees volunteered to plant a man-made bluff at the gritty site with bee- and bird-friendly species like hummingbird mint, beardtongue, and purple coneflower, and to erect bee nest blocks.
Restoring habitat for native bees can also restore our own connection to nature. Gordon Frankie’s campus bee garden has returned the well-traveled scientist to his roots in nearby neighborhoods, where he grew up eating locally grown food. He and his students are now working on integrating bee gardening, the food it produces, and healthy environments into an informal elementary curriculum. “It’s all about connecting the dots,” he says: “science, good soil, nutrition, physical activity—a healthy culture.”
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6 Tips for Attracting Native Bees
1. Select eight to 10 species native to your area (see the plant sidebar on page 30 and find additional resources at www.audubonmagazine.org to help you create a native bee habitat of your own). Exotic plants attract exotic bees, pushing out native species.
2. Don’t plant “pollen-less” or double-flowered horticultural varieties.
3. Pick plants that will flower at different times through the season.
4. Integrate patches of bee-friendly plants throughout your garden, especially in your vegetable patch, where they attract pollinators and increase yields.
5. Provide nest habitat in the form of “bee blocks,” as well as dead branches for boring bees and bare ground for ground-nesting species. (See the Xerces Society website for details.)
6. Avoid or eliminate pesticides.