One hot day last year, Sung Lee, an East Bay beekeeper who goes by the Bee Charmer on social media, got a call from a woman in Hayward about a bee swarm in her yard. He drove over to take a look. Far from a swarm, he found hundreds of Western honey bees (Apis melliflora) amassed on patches of freshly irrigated soil. They were, Lee realized, sucking up the last dregs of moisture before it evaporated in the summer heat. When Lee bent down to their level, they didn’t give him a second look. “It was like, ‘Yeah, talk to me later,’ ” Lee recalls. They had work to do, if they wanted to survive the summer.
It’s a common phenomenon in the heat: thirsty Western honey bees descend upon water sources from dripping laundry to leaky hoses. And scientists caution that as our temperatures continue to increase, so will the bees looking for relief in the heat.
Our mammal bodies can sweat, shiver, and adjust to (almost) any temperature. But bees are “not like us,” says Madeleine Ostwald, a postdoctoral researcher at UC Santa Barbara (UCSB) who studies how climate change impacts bee species. “When it’s hot out, the bee itself is hotter.” As the Bay Area heats up, our insects will have to adjust to survive.
We still know very little about how heat affects our most important pollinators, though, especially for our under-valued but ecologically critical native bee species. Armed with lizard egg incubators, test tubes, and bug nets, scientists across California are figuring out how bees might cope with a warming world—and which bees might need the most help to survive.
Though the small striped non-native honey bee might be the first that comes to mind for many, Apis melliflora is only one of the 300-plus bee species buzzing around the Bay Area. Our native bees range from inch-long, teddy-bear carpenter bees (Xylocopa spp.) to bead-like, parasitic species almost indistinguishable from flies. They span a spectrum from solitary to social, and nest everywhere from ground dens to grass stems. Gretchen LeBuhn, a biology professor at San Francisco State University, suspects bees heat up easily. “It’s a small temperature range between fine and not fine,” she says.
But does a heatwave mean the same thing to each bee? One of Ostwald’s students, UC Santa Barbara senior Nathalie Bonnet, designed an experiment to simulate heat waves on different bee species, including various taxa also found in the Bay Area. Out in the Channel Islands, the research team dove over flowers to net insects and then placed them in test tubes inside an adapted incubator originally made for lizard eggs. Bonnet set the temperature to 104º Fahrenheit, measured the humidity, and sat back and started a stopwatch. Her goal was to see how long it took different species to either die or reach a condition called heat stupor—essentially, a self-imposed coma.
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The experiments did ultimately culminate in killing most bees collected. Each bee ended up, however, in UC Santa Barbara’s collections, where insects find second lives as part of imaging, education, and research efforts. Bonnet initially felt bad about this, but says the research, which is based on similar studies on Belgian bees, is worth it, and will not impact any bee populations. As bee researchers just begin thinking about climate change, this study, Bonnet says, is “a little bit groundbreaking.”
The resilience of the bees surprised Bonnet, as did the diversity of their reactions. Carpenter bees—skilled in tunneling through small spaces—looked “very comfortable” squished in the test tubes, she says. Meanwhile, bumblebees—perhaps used to hyperactive flower-hopping—buzzed around in frantic confusion till they collapsed. Sometimes, the tiniest sweat bees (Halictidae) made it eight hours in heat and humidity that would sweat out any human. “I definitely had some times where I was like, ‘Okay, there’s no way that bee is still going,’ ” Bonnet says.
Bonnet is still processing her results, but some patterns have emerged already. Sex most often separated how much heat bees could stand, she found, an observation supported by other studies. “Males of all species just kind of sucked at putting up with heat,” Bonnet says. She’s still figuring out how different species’ traits might protect them as temperatures climb.
Before extreme heat kills bees, it affects how they act. Ostwald’s research focuses on how climate change might affect the bonds that hold bee societies together. Other studies have shown that some bee species become more aggressive as it gets hotter, possibly as bee activity escalates with temperatures. While most bees are solitary, Ostwald says sometimes that as temperatures and other environmental conditions change, they can become social, possibly to better cope as a group with extreme weather conditions.
Western honey bees use their social structures to their advantage during heatwaves. As hives heat up, specialized water-collectors start venturing out—worker bees whose main purpose is gathering water. They use waggle dances to signal to each other where to find mineralized waters, which they prefer, Lee says. And after slurping down every liquid they can find—from condensation to human sweat to the irrigated soil on a Hayward lawn—they gurgle back to the hive, where they regurgitate their liquid load by the hive’s baby bees and flap their wings to manufacture a makeshift air-conditioner. (It’s an adaptation so effective researchers have observed hives in actual lava fields still stay cool enough to remain in their livable range.)
Native bees don’t seem to have water-collecting deputies, though. And so how they’ll cope with climate change is an open research question. Ostwald studied how often-solitary carpenter bees can cuddle together to survive extreme cold—an often-ignored effect of climate change’s temperature impacts. By huddling together in big bee piles, they stayed much warmer than they would have on their own.
But summer heat is another story, and researchers like Ostwald are getting worried. While Bonnet collected bees last summer, another UCSB student experiment measured how hot bee dens got. Researchers believe that bees’ ground nests could be a cool refuge during heat waves, a place to wait out the worst of summer. But the initial measurement data (not yet finalized or published) suggests the ground nests got far hotter than any other bee haven.
More than the adult bees, who can fly somewhere shady, Ostwald is thinking about what might happen to the young bee brood stuck baking in an underground nest-turned-oven. Research has found baby bees exposed to high heat can emerge later with learning deficits, affecting their ability to figure out which flowers they can feed on. As a result, one heatwave’s legacy can last for years.
Our bees are already in an existential crisis, as they contend with pesticide applications, landscape change, invasive competitors, parasitic insects, and the loss of native plants. Extreme heat is just “one more thing,” says LeBuhn. “And maybe that one more thing is the rivet popping off the airplane.”
HOW TO LEND HOT BEES A HELPING HAND
While the research is still emerging on bees and heat, beekeepers and scientists have strategies they recommend for helping bees out! You can read more about them in this Bay Nature article.
For honey bees, Sung Lee recommends providing shallow water dishes where bees have cool places to perch – like a floating cork or marbles.
For native bees, native plants in your backyard is critical. This Bay Nature guide provides planting pointers.
Ostwald suggests also keeping nesting options in your yard, such as old plant material like twigs and leaves. Most importantly, don’t try and get rid of native bees—they’re here to help us.
Correction: An earlier version of this article misidentified the bee in the first photograph as a sweat bee. It is a yellow-faced bumblebee (Bombus vosnesenskii).
