John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Not to alarm you or anything.
A few years ago, John Hafernik detected in the walls of his house a thrumming hive of honeybees. He didn’t place a frantic call to the exterminator—he’s a bug-loving biologist at San Francisco State University—but grabbed some traps to experiment.
What he found was astonishing. Each dawn, his traps, which were equipped with lights, were filled with as many as 80 bees. That shouldn’t happen, because bees rarely go out at night; they use UV rays and polarized light to navigate and are “blind” without the sun. Even weirder, they swarmed the traps on January mornings when the weather was frosty. Cold kills bees. These were conditions in which no normal bee would be flying around.
The hive eventually died, which Hafernik credits with saving his marriage. “My wife was not excited about having bees in the walls,” says the 68-year-old San Franciscan. “The things we do for science.” But by then he had confirmed that his insect guests were the prey of a parasitic fly, Apocephalus borealis, that injected eggs into their bodies. For some reason that caused the bees to become deranged before perishing somewhat like the chest-bursting victim in Alien.
The ZomBee dance of death
Hafernik was originally responsible for discovering the gruesome interaction between honeybees and Apocephalus borealis. He noticed downed bees under electric lights in 2008 and put them in a jar as food for his lab’s praying mantises. He then forgot about the jar—when he came back, it was littered with brown pupae, which inspired a 2012 journal article fingering Apocephalus as the creator of what he calls “ZomBees.”
The fly had been known to parasitize bumblebees but not honeybees. The relationship might not have been noticed before, or perhaps it’s new. Hafernik favors the latter explanation. “If it was going on longer, there’d be more accounts from beekeepers and others,” he says.
At least one Bay Area beekeeper, Robert MacKimmie, has noticed an increase in afflicted specimens in recent years. “There are up to 200 bees a day or more disappearing from hives,” he says. On many mornings, he finds “bees in front of the hives crawling around in circles like they were drunk or poisoned.”
Here’s the “ZomBee” dance of death, in brief. Apocephalus, smaller than a fruit fly and looking like any other inconsequential pest, lands on a bee and jabs eggs through cracks in its abdomen. The parasite flies off and presumably expires thinking, “Job well done,” but it’s just the beginning of the host’s woes. The eggs mature, triggering something in bees that causes them to venture out at night in search of artificial light. They then fall to the ground and wander dazed as if they have neurological damage.
The night-stalking remains a mystery. “It’s quite possible it’s the parasite manipulating the host to move to a better place to complete its life cycle,” says Hafernik. “Or it could be the bee committing altruistic suicide, getting out of the hive to make it less likely other bees get infected.”
Whatever the reason, the bee then dies, only to start squirming in a week when maggots burst from its head or thorax. They wiggle away and form pupae to become adult flies and start the whole sequence anew. “Usually there’s a half-dozen or so [maggots] but occasionally you get a ‘lucky’ bee,” says Hafernik. “The record we have is 24 maggots coming out of a single bee.”
They’ve been spotted across North America
“ZomBees” have been found along the West Coast from Seattle to San Francisco to Santa Barbara. In a survey of 31 hives in the Bay Area, Hafernik found 77 percent were infected. “ZomBees” have also appeared in Vermont, Pennsylvania, the Hudson Valley, and South Dakota. Given that the parasite ranges all across North America, they could be in many other places.
Hafernik tracks sightings at ZomBee Watch, which geolocates reports from citizen scientists and answers questions like “Are parasitized honeybees more aggressive than normal?” (Unlike Hollywood zombies, they’re not, but still can sting if handled without forceps.)
Getting a bead on the extent of the infestation is important, as honeybees play a huge role in agricultural pollination and are already beset with afflictions, from blood-sucking Varroa destructor mites to pesticides to fungal diseases to dysentery. With all these things harming bee populations, it’s hard to tell what role Apocephalus might play in Colony Collapse Disorder. “Most people who work on Colony Collapse Disorder think it’s caused by a variety of things acting simultaneously on bee colonies,” says Hafernik.
But aside from helping a species and an industry, keeping ZomBees in check is a smart move because, seriously, do you want to live in a world with dying, nocturnal bees kamikazeing into your windows and lamps? “That’s been a big problem for me,” says MacKimmie, who’s moved several of his hives due to complaints—including from one house where exhausted and dying ZomBees piled up so much the landlord had to blast them away with a leaf blower.
“My neighbors have sliding glass doors … and on warm nights they'd leave them open,” he says. “These bees that were infected would hit their porch light, then come in to look for other lights at night. So they had a dozen bees in their house and were kind of freaking out about it.”