Native bees face many threats, but gardeners can help these indispensable pollinators
PORTLAND, OREGON'S, SABIN ELEMENTARY SCHOOL takes pride in its unusual mascot: a half-inch-long, blackish-brown bee in the genus Andrena, or affectionately known by students, parents and teachers as “the tickle bee.”
For two months each spring, thousands of these furry, ground-nesting insects emerge from holes scattered across the school’s baseball diamond, soccer and kickball fields and even the bare dirt beneath benches. “On warm days, when bees are flying in search of nectar, you can’t walk across a field without bumping into dozens of them,” says Mace Vaughan, a Sabin school parent and pollinator program co-director for the Xerces Society for Invertebrate Conservation. If you pick up and hold one of the bees in your hand—as many children do—the insects don’t sting but do, indeed, tickle.
In many ways, tickle bees are typical of North America’s more than 4,000 native-bee species. Unlike the familiar honey bee, imported from Europe in the mid-1600s, more than 95 percent of natives live not with other bees in hives but alone in small nests carved into soil or wood. Native bees tend to be tiny, do not have queens or produce honey and rarely sting. “Most people have no idea what the majority of our native bees look or behave like,” says Xerces Society Executive Director Scott Black.
Facing major threats, including habitat loss, disease, climate change and pesticides, these critical pollinators also are poorly known by scientists. Unlike larger and better-studied insects such as butterflies and dragonflies, most bees must be captured and examined under microscopes to be identified. Even then, distinguishing one species from another entails “a horrendous amount of minutia” that only a handful of experts have mastered, says biologist Sam Droege, who heads the U.S. Geological Survey’s (USGS) Bee Inventory and Monitoring Lab. As one of those experts, Droege recently launched an ambitious project to survey and track the status of the continent’s thousands of bee species, starting with an all-volunteer effort that will target the Mid-Atlantic region.
Learning the status of native bees is vital. Animal pollinators such as bees, birds, butterflies and bats are essential to the reproduction of nearly 85 percent of the world’s flowering plants. By far the most important of these animals are bees, making them, in Black’s words, “essential to the entire fabric of life on the planet.”
Bees also are needed to produce more than a third of all foods and beverages humans consume. “In the United States alone, native bees contribute at least $3 billion a year to the farm economy,” says Vaughan. In the future, they may play an even more important role if domestic honey bees continue to decline due to colony-collapse disorder (CCD)—a mysterious phenomenon that causes worker bees to abandon hives—as well as pesticides, mites, disease and other problems.
According to scientists, natives are more than up to the task of filling in for beleaguered honey bees. In a study published in Ecology Letters, for example, ecologist Rachael Winfree of Rutgers University discovered that in the Delaware Valley of New Jersey and Pennsylvania, visits by more than 40 wild-bee species to watermelon flowers were sufficient to pollinate the crop on 21 of 23 farms in her study site. “If we lost all honey bees here tomorrow, between 88 and 90 percent of the crop would be fine,” she says. Even on larger farms that truck in honey-bee hives, Winfree has found that natives pollinate up to a quarter of commercial cranberry and blueberry crops.
As scientists like Winfree uncover evidence bolstering the value of native bees, others are finding worrisome signs that the insects may be in trouble. In one study published recently in the Proceedings of the National Academy of Sciences, researchers from the University of Vermont’s Gund Institute for Ecological Economics, working with colleagues nationwide, created a computer model combining federal land-use databases with input from bee experts. The model suggested that between 2008 and 2013, bee abundance declined across 23 percent of the United States.
More troubling, the researchers noted the greatest declines in areas like the Midwest and California’s Central Valley, where farmers grow crops that rely most heavily on bees, including apples, almonds, peaches and blueberries. “What this means for farmers may be lower and more inconsistent yields as well as higher costs for honey bees,” says coauthor and Gund Institute Director Taylor Ricketts. “For the rest of us, it may mean a more expensive and less stable food supply.”
Calling the study “a good first step to assess the status of bees nationwide,” Black points out that biologists still lack baseline data on the majority of native-bee species and how their populations have changed. One notable exception, he says, are the bumble bees, and the news about these familiar fliers—particularly important crop and native-plant pollinators—is bad.
During the past two decades, scientists report, four once-common and widespread North American bumble-bee species—the western, rusty patched (right), yellow-banded and American bumble bee—have vanished from large portions of their former ranges. A fifth—Franklin’s bumble bee—already may be extinct. A soon-to-be-published Xerces Society analysis, conducted with the Bumblebee Specialist Group of the International Union for Conservation of Nature (IUCN), concludes that more than a quarter of the continent’s 47 bumble-bee species “face some level of extinction risk.”
For some of the most imperiled bumble bees, “evidence points to disease as the primary culprit,” says Robbin Thorp, a biologist and professor emeritus at the University of California–Davis who has studied the insects’ decline for 20 years. Thorp believes that when bumble-bee queens were shipped to Europe in the early 1990s—to generate new colonies to pollinate U.S. crops—their descendents brought back a nonnative parasitic fungus that spread rapidly among wild bees lacking prior exposure to the pathogen. Though the federal government today bans bumble-bee shipments between Europe and the United States, scientists remain worried about unregulated trade within North America. As demand grows for bumble-bee-pollinated crops, especially tomatoes, large commercial producers ship increasing numbers of the insects—and potentially their diseases—to parts of the continent where they are not native.
Disease is far from the only threat bumble bees and other native bees face. Pollinators today “live in such a topsy-turvy world it can be hard to pin their troubles on a single cause,” Black says. In addition to disease, he says the most significant threats are habitat loss, pesticides and climate change.
Recently, the danger climate change poses was in the news, following a study published in Science analyzing more than 400,000 bumble-bee observations in North America and Europe dating back to the beginning of the 20th century. The researchers reported that, unlike many animal species whose ranges are shifting northward as temperatures rise, the distributions of most bumble bees are not pushing north. At the same time, the insects are disappearing from southern portions of their ranges. “Global warming seems to have trapped bumble bees in a climate vise,” says lead author and University of Ottawa biologist Jeremy Kerr.
Scientists also are increasingly worried about pesticides. Of particular concern is a new class of insecticides, the neonicotinoids, that are long lasting and absorbed by plants’ vascular systems—meaning bees are exposed when they eat nectar and pollen. Beyond killing the insects, “research shows that these compounds have sublethal effects on bumble bees, including reduced foraging and reproduction,” says Sarina Jepsen, Xerces Society endangered species program director and deputy chair of the IUCN Bumblebee Specialist Group.
Meanwhile, “we see increasing evidence that neonicotinoids are leaking out of farmlands to impact bees in places the chemicals were not sprayed,” says the USGS’s Droege. That evidence includes a recent study by his agency that examined wild-bee exposure to pesticides in wheat fields as well as nearby grasslands in northeastern Colorado. During two field seasons, the federal biologists found 19 pesticides and their breakdown products in 70 percent of the bees collected from both habitats. The most frequently detected poison was the potent neonicotinoid thiamethoxam.
But the buzz about bees is not all bad. In recent years, public interest and concern about the insects has increased, fueled in part by well-publicized losses of honey bees to CCD. “Colony-collapse disorder turned out to have a bit of a silver lining,” Black says. “Now more people know that the food they eat depends on animal pollinators.”
Even the White House has come on board. Last spring, President Barack Obama announced a new federal strategy to protect bees and other pollinators. Progress since then includes steps by the U.S. Department of Transportation to encourage planting pollinator habitat along highways (see Habitat Highways). And the U.S. Fish and Wildlife Service recently proposed listing seven species of Hawaiian yellow-faced bee as endangered—which, if approved, would be the first bees ever to receive protection under the U.S. Endangered Species Act.
At the same time, researchers and citizen scientists have been spotting two of the continent’s rarest bumble bees—the western and rusty patched bumble bee—in parts of the country where they had disappeared, from Oregon to Ohio. To Thorp, these sightings “support the disease hypothesis and suggest that some bees carrying resistance to the nonnative pathogen survived and are now passing resistance genes to their progeny.”
The best bee news of all, though, may be that anyone with just a tiny piece of land can help these critical pollinators. “Bees are not bison,” Droege says. “Anywhere you have good, pesticide-free habitat, even as small as a suburban backyard, you are likely to find a good diversity and abundance of native bees.”
Photographed in the wild then released unharmed, these North American native bees—not life-size but proportionate to each other—hint at the vast diversity of our most important plant pollinators.
By cultivating sunflowers (below, with a Hunts bumblebee) and other native plants, gardeners can help native bees. Here are a few tips:
Provide pollen and nectar for food: Active from early spring through late fall, bees need access to a variety of nectar- and pollen-producing flowers that bloom at different times. Native plants are best because they require less maintenance, have coevolved with indigenous bees and—unlike many nonnatives and cultivars of natives bred for showy blooms—reliably produce nectar and pollen.
Ensure bees have nesting sites: In contrast to hive-dwelling honey bees, most native bees nest alone in small holes on open, sandy ground or in brush piles, tree snags, logs or excavated twigs. Supplement such natural nest sites with bundles of hollow plant stems or wooden mason-bee houses. Reduce mulching, mowing and tilling that may destroy nests or future nesting sites.
Eliminate pesticides: Avoid insecticides (which kill bees directly) and herbicides (which kill the plants bees depend on). In particular, steer clear of systemic insecticides such as neonicotinoids, which are taken up by the vascular systems of plants. This means bees feeding on pollen and nectar are exposed to powerful poisons long after the chemicals have been applied.
Help scientists study bees: Particularly important pollinators of both crops and native plants, many bumble-bee species are declining. Help scientists learn more about the insects by reporting bees you see in your garden to the citizen-science project Bumble Bee Watch.
For more than four decades, the National Wildlife Federation has encouraged homeowners, schools, communities and others to create habitat for bees and other pollinators though its Garden for Wildlife™ program. Last summer, the Federation stepped up these efforts, joining with dozens of gardening, seed and conservation groups to launch a nationwide campaign: the Million Pollinator Garden Challenge. Campaign participants are rallying hundreds of thousands of people across the country to create 1 million new pollinator gardens by the end of 2016. “Pollinators are keystone species that provide the foundation of our ecosystems,” explained NWF President Collin O’Mara at a June 2015 press conference announcing the campaign.
To learn more, visit www.nwf.org/nwfgarden.
Laura Tangley is senior editor - and a bee-friendly wildlife gardener. Clay Bolt is a natural-history photographer who, through his Beautiful Bees project, is documenting North America's native-bee species.
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On the Trail of Native Bees: An effort to assess the status of wild bee species
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