Small Wonders: The Plight and Promise of California’s Native Bees

A black-tailed bumble bee (Bombus melanopygus) on a shooting star (Primula sp.) in Yosemite National Park. Photo: Michelle Duennes

This story first appeared in the Fall 2020 issue of Flora. 

By Emily Underwood

“In 2007, biologist Gretchen LeBuhn discovered an unusual winged visitor in one of San Francisco’s city
parks: a black bee with rust-colored fuzz and pale yellow stripes which she and her students identified as the California native wool carder bee, Anthidium palliventre.

Coast buckwheat (Erigonum latifolium) growing on the northwestern coast of the Point Reyes National Seashore. The wool carder bee uses fibers scraped from the buckwheat’s soft leaves to line its nest in sand dunes. Photo: Elizabeth Kubey

The bee uses its bristled legs to dig a nest in sand dunes, then scrapes hairs from the leaves of coast buckwheat (Erigonum latifolium) to line its nest with soft fluff. Like many other dune-dwelling bees it was once a San Francisco local, sipping nectar from lupine and other coastal scrub wildflowers.

But when developers paved over most of the dunes on the peninsula, the bees lost their homes. “They’re little representatives of the history of the land,” LeBuhn says, speculating that the few other wool carder bees she’s found may dig their nests in sandboxes.

The wool carder bee is just one of many “small wonders” that LeBuhn and her team at San Francisco State University have found in the city’s parks. Even a tiny one-acre park can attract as many as 30-40 native bee species if they have lots of flowers and good nesting spaces. Planting native wildflowers is particularly important to support the state’s specialist bees, which have evolved to prefer just one or a few types of plants, LeBuhn says: “People think [pollinator loss] is an awful and daunting issue, but I think we can all help.”

The roughly 100 or so native bee species that LeBuhn has documented within San Francisco is roughly half of what she would expect to find there, based on surveys in nearby Marin County and the East Bay area. Although the peninsula may historically have had fewer species, LeBuhn attributes at least some loss to development. “San Francisco has fewer bee species than it would if it was wild,” she says. “Nobody’s going to be surprised by that.”

A wool carder bee (Anthidium palliventre) photographed in a San Francisco city park by one of biologist Gretchen LeBuhn’s graduate students, Nevin Cullen.

Like many pollinators, including bats, birds, butterflies, moths, flies, beetles and small mammals, a number of California’s wild bee species are under threat. The best-studied declines are in bumble bees: In 2019, for example, the California Fish and Game Commission voted in favor of listing four species of California bumble bee under the California Endangered Species Act, including Crotch’s bumble bee (Bombus crotchii), Franklin’s bumble bee (Bombus franklini), Suckley cuckoo bumble bee (Bombus suckleyi), and the western bumble bee (Bombus occidentalis occidentalis).

For other native bee species, data are sparse or nonexistent. “We have no idea how many species are doing,” says Hollis Woodard, an entomologist at UC Riverside who studies the life cycles of bumble bee queens. To start filling those data gaps, Woodard recently helped launch a scientific consortium called the National Native Bee Monitoring Network. Meanwhile, LeBuhn and her team at San Francisco State University are running a decades-long community science effort called The Great Sunflower Project, in which gardeners across the country record what bee species come to visit.

The declining Suckley’s cuckoo bumble bee. Photo: Hadel Go/CC BY 3.0

Of the roughly 20,000 bee species found throughout the world and 3,600 native bee species in North America, California is home to 1,600. It’s hard to overstate the dazzling variety of wild bees in California, which CNPS former executive director Dan Gluesenkamp describes as “the Amazon Basin of bee diversity.” Some are tiny, like the fruit-fly-sized Perdita minima, which pollinates minute desert wildflowers such as whitemargin sandmat (Chamaesyce albomarginata). Others are big, like the male Valley carpen- ter bee (Xylocopa varipuncta), a fuzzy golden bee that some scientists refer to as a “teddy bear.”

Unlike the social, non-native western honeybee (Apis mellifera), most of California’s native bees live solitary life-styles. Some bees nest in the ground in abandoned cavities; others, like the wool carder bee, dig or build their own nests. Some shelter inside trees, others in rock walls or even abandoned snailshells. There are red, black, and blue bees, and metallic green “sweat” bees that drink human perspiration.

Despite the kaleidoscopic array of native bees, western honeybees have long received the majority of public attention and research dollars because they are so important to agriculture, says LeBuhn. The United States Department of Agriculture (USDA) values the total annual contribution of honeybee products and pollination services at $700 million. At least in the United States, however, the loss of honeybees “is an agricultural issue, not a conservation issue,” says Woodard. “They’re not native, and they’re completely entangled with our agricultural system, many aspects of which are not sustainable.”

Left to right: A turret-building chimney bee (Diadasia sp.) on chaparral mallow (Malacothamnus fasciculatus); mining bee (Adrena sp.) on Channel Islands tree poppy (Dendromecon harfordii); striped sweat bee (Agapostemon sp.) on Guadalupe Island globemallow (Sphaeralcea sulphurea). Photos: Kris Ethington

California is the Amazon Basin of bee diversity.”
– Former CNPS Executive Director Dan Gluesenkamp

In the early 2000s, scientists coined the term “colony collapse disorder” (CCD) for a mysterious syndrome that was decimating domesticated honeybee populations. Although scientists still aren’t sure what causes CCD, they think it arises from a combination of pests such as the varroa mite parasite, disease, poor nutrition, pesticide exposure and other stressors, such as being transported by truck from farm to farm. The syndrome still poses a major threat: From April 2019-2020, beekeepers lost more than 40 percent of their colonies to CCD, the USDA reports.

The plight of managed honeybees raised alarms that native bees might be facing similar challenges, says Neal Williams, a pollination ecologist at UC Davis. Although most native bees don’t live in colonies like honeybees do, they too are susceptible to poor diet and loss of habitat, he says.

Protecting native bees can be an important insurance policy against the loss of honeybees, Williams and his colleagues have found. In a 2002 article in the Proceedings of the National Academy of Science, for example, Williams, the late entomologist Robbin Thorp, and conservation biologist Claire Kremen found that for organic farms located close to native bee habitat, such as oak woodlands and chaparral, “free” pollination from native bees was sufficient to grow even demanding crops like watermelon, which requires up to 1000 grains of pollen to produce a single melon.

Native squash bees (Peponapis pruinosa) are highly effective pollinators for cultivated squash, melons, and other crops.
Photo: Ilona Loser, CC-BY-SA-4.0

A number of other studies have shown that native bees can outperform honeybees in pollination. Bumble bees, for example, use a messy method called buzz pollination to vibrate the flower and shake more pollen loose. The technique which appears more effective than honeybee pollination for crops including tomatoes, peaches, and a number of native plants, among them huckleberries and manzanitas.

The quality of pollination — how many grains of pollen get from the male to female parts of a flower — matters for the quality of food. Well-pollinated melons are bigger and firmer, apples rounder. Well-pollinated cultivated strawberries (descendants of California’s native beach strawberry, Fragaria chiloensis) are more perfectly formed and redder.

Our agricultural system threatens native and non-native bees alike, says Williams. In California, many small plots with flowering borders have been consolidated into large, homogeneous zones that provide poor bee forage and habitat. A good example is CA Route 99 through the Central Valley, with its large swathes of suburban development crops. “I wouldn’t want to be a bee there,” Williams says. Crops such as corn and wheat are not typically pollinated by bees, LeBuhn adds, so a conventional corn field doused in pesticides “is about as barren as you can get.”

Most people like the idea of supporting bees — the question is how to do it, says Williams. “I think that a grower, a conservation biologist, a commodity board member would all agree that we would like to support native bees, but that’s a pretty nebulous statement.”

At UC Davis and Hedgerow Farms, a native seed company in Winters, California, Williams and postdoc Uta Muller have been testing native wildflower mixes to see which are most attractive to native bees and other pollinators. The team has planted gridded plots with native wildflowers such as California poppy, phacelia, native sunflowers, and coyote mint. In a laborious process, they’re now counting and identifying the native bees that visit each plot once a week, for nine months. “We run through every plot once in the morning, take a quick break in the middle of the day, then repeat the whole thing,” Williams says.

Through this and previous experiments, Williams thinks he’s now got a pretty good grasp of what plants different species of bees prefer. But he’s still trying to suss out how much land a farmer needs to plant in order to make a real difference — “Is it five percent, 10 percent?”

Working with the Xerces Society, Hedgerow Farms, and other collaborators, Williams ultimately hopes to develop computer algorithms that will suggest the best seed mix for a given purpose, whether that’s supporting rare bee species, providing food for as many different bee species as possible throughout the year, or supplementing honeybee crop pollination. He’s also trying to get the cost of seed mixes down. At present, planting a pollinator mix purchased from the Natural Resources Conservation Service might cost a farmer $500-700 an acre, and he wants to reduce the cost down to a third or a fifth of that, or even less, he says. One challenge is to create seed mixes that not only suit pollinators, but humans, he says. “People will say, ‘I want to support pollinators, but I also want things that are red, blue and yellow blooming in all three seasons.’”

The native wildflower pollinator seed mix trials at UC Davis Student Farm in April 2020. Photo: Williams Lab UC Davis.

Gardeners should use local wildflower seed mixes of known genetic origin, like those sold at Hedgerow Farms, notes CNPS Director of Biodiversity Iniatives Andrea Williams. When people plant non-local wildflowers, they run the risk of wiping out local species through hybridization. A good illustration of why local seeds are preferable is the iconic Texas bluebonnet (Lupinus texensis). By using bulk seed from out of state, Texas has “hybridized their state flower out of existence — they don’t have any local variation anymore,” Williams says. “We don’t want that to happen to our state flora.”

Unlike California’s native plants, which have been extensively mapped thanks to organizations like CNPS, there’s scant information about how many of California’s native bee species are distributed throughout the state, and thus how climate change, development and other factors are affecting them, LeBuhn says. “It’s amazing how much we don’t know.” One way people can help scientists is to participate in community science projects like the one she is running, the Great Sunflower Project. The project needs more volunteers, particularly in rural areas, she says. Gardeners can also find lists of bee-friendly plants on CNPS’s Calscape.org and on the Xerces Society website.

Habitat loss is only one of the many threats that bees face, Neal Williams notes. Neurotoxic pesticides like neonicotinoids may be interfering with bees’ ability to forage, while pathogens like varroa mites and nosema disease, and environmental factors like drought exacerbate bees’ susceptibility to disease. Just like in people, Williams says, “If we stress ourselves, then disease or parasites have a greater impact.” To better understand how California’s bees are responding to pesticides, Williams is measuring pesticide residues in the pollen that bees collect, which he’ll use to develop a map of exposure over space and time. At UC Riverside, Woodard is running lab experiments to study how pesticides affect the brains of bumble bee queens.

UC Riverside entomologist Hollis Woodard and her team are studying bumble bee queens in the Sierra Nevada. Photo courtesy of Hollis Woodard.

High in the Sierra Nevada, Woodard and her team are also studying what bumble bee queens need to thrive at different stages of their life cycle, in order to better understand how they’ll respond to climate change and find ways of supporting the bees throughout the year. It’s an urgent question, as climate change appears to be driving many bumble bee species worldwide toward extinction: In a February 2020 Science study of 66 bumble bee species in North America and Europe, for example, researchers found that as temperatures have climbed, the chances of a bumble bee population surviving in any given location has dropped by an average of 30 percent.


A manzanita wonderland

California is a hotspot for manzanita diversity, with roughly 100 species and subspecies of manzanita, 59 of which are so rare they only grow in one wild place. There’s hardly a more Californian shrub, growing from coast to mountaintop, with many species’ survival tied to fire, fog, and introduced pathogens. When planting manzanita to support native bees, it’s a good idea to use local species, says CNPS Director of Biodiversity Initiatives Andrea Williams.

Left to right: Hoary manzanita (Arctostaphylos canescens ssp. canescens) Photo: Morgan Stickrod. The rare Santa Margarita manzanita (Arctostaphylos pilosula) Photo: garmonb0zia/iNaturalist CC0. Endangered Mount Diablo manzanita (Arctostaphylos auriculata) Photo: Al Kordesch.

Bumble bee queens spend much of their lives alone, wintering underground and emerging in the spring. In many areas of California, observers can spot the queens feeding on early-blooming native plants like manzanita (Arctostaphylos spp.) as early as February; by shivering their flight muscles the queens can raise their body temperatures in cold weather.

A yellow-faced bumble bee (Bombus vosnesenskii) on manzanita (Arctostaphylos sp.) in Sierra National Forest. Photo: Erica Sarro

Once the queens have fattened up, they start flying low over the ground in a zigzag pattern, looking for a cavity to nest in. After making a thimble-sized pot of honey and a small mound of pollen as a food reserve, they start laying eggs and incubating them. When a larva hatches, a queen bumble bee will regurgitate food into its wax pot “like a mama bird,” Woodard says. About two weeks later, the larvae chew their way out and become the first workers.

If solo bumble bee queens don’t get the food that they need in early spring, or can’t find a nest, they won’t be able to produce a colony. “It’s a really tenuous point in the life cycle,” Woodard says. She wants to know how these intrepid queens get by in parts of California where manzanita doesn’t grow, and how they handle the unpredictable weather of early spring, when there can be flowers in bloom one warm day, and snow the next.

Woodard’s and her team’s careful observations of queen bumble bees throughout the year underscore just how many different kinds of flowering plants are needed to support a colony, she says. “It’s not just early-blooming plants, but the full season that matters, all the way through the end.”

For gardeners and others who want to support native bee populations, increasing the number of flowering plants that are available starting in February and lasting all the way into the fall can provide critical support, she says. “When you scale that out to all the other pollinators, you think, ‘Oh my gosh, we need flowers everywhere.’”

UC Riverside PhD student Natalie Fisher in Yosemite National Park. Photo: Hollis Woodard

Emily Underwood is the Publications Editor for CNPS.  

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