Burlingame beekeeper Bob Silverstein checks a frame from one of his hives. (Photo by Philip Wartena)

Varroa mites are a tiny apocalypse annihilating bee hives and dividing an otherwise cooperative community.

Story by Kali Shiloh // Photos by Philip Wartena

Sometimes Bob Silverstein rolls his bees in sugar. It’s the gentler approach to removing the parasites that often infest his hives.

When he aims for accuracy though, he can’t be gentle: he grabs a metal measuring cup and a glass mason jar with a small mesh screen for a lid and brings them out to the six beehives in his backyard. Then he opens a hive, scoops out a half cup of bees and seals them in the jar. Quickly, he pours rubbing alcohol onto the 300 buzzing martyrs and swishes vigorously, drowning them all.

When the body of every bee is soaked, he drains the liquid through the mesh lid and counts the black spots that come out with it — each one is a varroa mite. If he counts too many, Silverstein — a retired orthopedic surgeon — will treat the infected hive with an oxalic acid vapor, which he likens to a doctor treating his patients.

Bob Silverstein primes a jar for an alcohol wash to detect mites. (Photo by Philip Wartena)

Silverstein and hundreds of other beekeepers on the Peninsula treat their hives in a desperate attempt to fight off the deadly mites, but many fellow beekeepers are trying to let the plague take its natural course instead. In order for that to work, they say, every beekeeper has to stop treating.

The worldwide mite epidemic is one of the first things new beekeepers learn about when they start tending bees on the Peninsula. The next thing they learn is that they have to pick a side. “It’s almost a religious divide among beekeepers,” says Tori Muir, former president of the Beekeepers’ Guild of San Mateo County. Muir, Silverstein and other treaters use noxious strips and sprays to keep mite populations down and give colonies a chance at survival, but treatment-free beekeepers say that interferes with natural selection — that the bees will evolve defense mechanisms if left alone.

With mites killing 40% of the country’s honey bee colonies every year, locals are still struggling to come to a consensus. The hobbyist beekeepers on the Peninsula may repair broken bones, engineer algorithms at Tesla and teach at Stanford during the day, but the science behind the lethal mite epidemic has them locked in a conflict that pits evolution against chemistry, with little room for middle ground.

Burlingame beekeeper Bob Silverstein (left) and a detailed view of his bees. (Photos by Philip Wartena)

Mite bombs and “don’t treat” guys

When Silverstein tells people he keeps bees, they always ask if he gets stung. He was stung 80 times last year, but he says he hardly notices anymore. Even though he can tolerate bee venom, he and his wife keep extra EpiPens at their house for visitors. A couple of his fellow Guild members have gone into anaphylactic shock after one sting too many, though that doesn’t necessarily stop them from beekeeping. Like Silverstein, they’re drawn to bee colonies with a fierce desire to better understand and advocate on behalf of the fragile species. In the height of summer, local colonies swell with as many as 60,000 bees, but that number can plummet to zero when varroa mites move in.

Silverstein and his beekeeping partner manage 21 hives scattered around the Burlingame area. Last year, Silverstein treated 16 of their hives for mites, but the five at his partner’s house were left untouched. “He’s one of these ‘don’t treat’ guys, so his yard we did not treat,” says Silverstein. Silverstein only lost three of his 16 hives to varroa mites — his partner lost all but one.

A closeup view of a varroa mite on the head of a bee pupa (Image by Gilles San Martin)

Some treaters refer to those five untreated hives as “mite bombs,” sending out shrapnel in the form of mite-laden bees. Bees fly at least two miles from their hive to forage for food each day, and they sometimes visit other hives, so many beekeepers note that the decision to treat or not treat has the potential to affect all other hives in a two-mile radius, even treated ones that might otherwise be spared.

“It’s an inflammatory term — ‘varroa bomb,’” says Silverstein. “It’s meant to stimulate non-treaters to treat because it’s trying to shame them by saying, ‘your bees are killing all your neighbors’ hives.’”

A bee born with Deformed Wing Virus. (Photo by Emily Parker of Bee & Bloom)

Whether they treat or not, all beekeepers agree that death by varroa is traumatic. After nesting in brood chambers alongside growing bee pupae, varroa mites hatch and pierce through the abdomen of adult bees to feast on a tissue called “fatty tissue,” which helps control the bee’s immune system. This weakens the bees and leaves them highly susceptible to crippling diseases like Deformed Wing Virus. “I’m a proponent of treating the bees because the varroa exact a very large toll on the bees,” Silverstein says. “I look at bees like I looked at my patients. If they got an illness or a disease I wouldn’t just let them have the disease. I’d try and do something about it.”

But the treatment-free Beekeepers’ Guild members are trying to do something different, and that polarizing choice can create tension. At one point, the friction over treatment was palpable at the monthly Guild meetings. “Whenever we have a lecturer,” says Muir (the former Guild president), “there is frequently a gentle reminder: Now, we all have different opinions here, and we’re all gonna be nice about it, aren’t we?” Although Guild members are generally collaborative, the strong opinions voiced by the most active members reflect a profound schism that still divides the community.

“I’m a proponent of treating the bees because the varroa exact a very large toll on the bees,” Silverstein says. “I look at bees like I looked at my patients. If they got an illness or a disease I wouldn’t just let them have the disease. I’d try and do something about it.” (Photos by Philip Wartena)

Splitting hives, importing queens

It’s not just the locals grappling with the mites’ impact on honey bees and, therefore, agriculture. The poppy seed-size parasites reproduce with such devastating efficiency that Australia is the only continent still free of varroa. Around shipping ports, the Australian government has set up sentinel hives — colonies that are heavily monitored to quickly detect the presence of varroa — in an effort to ward off the mites and protect the bees that pollinate their crops. In 2018, when dead bees were found on an American ship about to dock in Melbourne, authorities located the hive, blasted it with powerful insecticide to kill the colony, then set up a 2km surveillance zone in accordance with quarantine protocol to ensure not a single contaminated bee had escaped.

Comparatively, local beekeepers are hardly extreme when it comes to mites, but the intensity of the debate can still be uncomfortable for novice beekeepers just looking to enjoy a new hobby. The former mayor of Mountain View Mike Kasperzak, didn’t get into beekeeping to save the bees. In fact, he never expected to go into beekeeping at all. He’d developed a fear of bees in childhood after stepping into a hive, sustaining forty stings to the foot, and spending a day drifting in and out of consciousness from the venom. But when beekeeping ordinances became a popular topic in City Council meetings, Kasperzak decided to get to know the species better by setting up two hives. He now loves working with his bees and only occasionally sees animosity over treatment on social media, but he did once get “flamed” in an online forum. When he asked a question about hive splitting — a chemical-free method of interrupting the mite breeding cycle — another beekeeper responded by saying, “Well, congratulations, you just killed both your hives.” Small interactions like that don’t seem to faze Kasperzak, but other beekeepers find the debate more personal.

Left: European honey bee with a Varroa mite on its back (photo by Scott Bauer, USDA Agricultural Research Service, Bugwood.org); Right: a dead bee with Deformed Wing Virus (photo by Stefan de Konink)

Menlo Park resident David Wuertele — another treatment-free beekeeper — watched all three of his hives die last year, but he doesn’t think it’s because his treatment-free practices “killed” his bees. On the contrary, from his perspective the beekeepers who treat are the ones exacerbating the problem. “I believe that any attempt to treat mites prevents evolution from improving our gene stock, and interferes with treatment-free beekeepers’ efforts,” he writes via email. Wuertele — a software engineer at Tesla — sees initial losses as a part of the process of genetic evolution, which would result in stronger bees if treaters stopped keeping genetically weak bees alive with chemicals.

“Your non-treaters say you’re basically coddling wimpy bees,” says Muir, who treats. She’s heard many arguments from Guild members espousing natural approaches in order to both facilitate evolution and keep honey organic. “Not meaning to denigrate anyone,” Muir says of the treatment-free crowd, “I typically see the most strongly held opinions in either the people who’ve barely begun beekeeping and have done a lot of reading, or we have some [longtime beekeepers] who’ve been doing it for 35 years, and they’re pretty set in their ways.”

Fellow Guild member Nickie Irvine doesn’t quite fit either of those characterizations. She’s been beekeeping for 15 years, and her methods constantly evolve. After teaching environmental anthropology at Stanford for 25 years, Irvine was well-versed in research and the scientific method, and she now approaches each of her backyard hives as a genetics experiment to test different ways of reducing varroa numbers without resorting to chemical treatments.

When word spread that some Russian bees had adapted to better withstand varroa, she bought queens from those colonies. “The USDA imported bees from Russia,” Irvine explains, “and they indeed have much lower varroa levels. So one of the things we try are Russian queens and other queens that have been shown to have better resistance.”

Silverstein and his wife examining a hive while outfitted in their protective suits. (Photo by Philip Wartena)

If she sees good resistance in a hive — from Russian or other strong genes — she’ll split the hive so the strong bees can raise a new queen, which creates two healthy hives from one. Other times she’ll graft larvae from one hive into another to spread the strength of the gene pool. If a queen isn’t laying enough worker bee eggs, she can replace the weak queen with a stronger one.

There’s no shortage of creative (if not complex) alternatives to treatment, so in the quest for a solution to the varroa epidemic, Irvine would like to see more tolerance of beekeepers like her who explore alternative methods of varroa abatement. “This kind of general anger toward people who don’t treat . . . We need to let more people experiment to see what works and what doesn’t,” she says. But while she’s tolerant of the short-term attempts of treaters to mitigate losses, she ultimately views genetics as the only solution: “I don’t see how we’re going to get any selection for a better population [of bees] unless we effectively treat very little.”

Healthy bees and an abundance of honey from Silverstein’s surviving hives. (Photos by Philip Wartena)


On the Peninsula, no sentinel hives can warn beekeepers, because the mites have been in California since at least 1989. The question is not if a hive will get varroa, it’s when. Many backyard beekeepers weigh factors like honey production, the bees’ suffering and chemical toxicity when considering treatment options, but those aren’t necessarily in line with the nature of a hive. “Bees are brutally community minded,” Muir says. “It’s all about what helps us — [the colony] — survive. There’s no cult of personality or anything — with them it’s just about metrics.” She explains how in winter, when resources are scarce, the colony will push drone bees out of the hive to starve. Or, if a queen is underperforming, how the colony will raise a new queen and huddle around the old one, beating their wings furiously until she explodes from the heat. It’s a merciless version of altruism that few beekeepers dare simulate.

Irvine doesn’t think she could stomach killing an entire colony suffering from high numbers of varroa mites — which some researchers advocate — but she’ll move larvae and buy queens. Silverstein and Muir prefer the oxalic acid treatment, but every approach has its tradeoffs. “The people who monitor for mites year round and treat whenever the mite population starts spiking up, they [rarely] lose hives,” Muir says. “But very few people want to keep bees that way, and at some point you have to question — you’re keeping them alive, but at what cost, because you’re constantly treating for mites.”

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