It was a dark December night, which is why the lights were on outside the biology building at San Francisco State University, where a professor named John Hafernik studies bees, butterflies, beetles, and other insects of note. Those lights, illuminating his building’s entryway, would catapult Hafernik into a story that reads like a mystery novel—or at least a B movie. Scattered on the sidewalk, just beneath the flickering bulbs, were a handful of honeybees.

Zombie honeybees.

Hafernik didn’t know that yet, though. This was back in 2008, when the term “ZomBee” didn’t exist yet, because he hadn’t coined it. This was back before beekeepers from South Dakota to California to Washington State had begun to discover one after another of the poor zombified creatures, infected by a pernicious fly whose very survival depends on preying on the innocent. Last month, the bees showed up in Oregon. Scientists are now debating whether this spooky affliction could explain a bigger horror story: Colony Collapse Disorder, which has wiped out up to a quarter of beehives across America. 

All Hafernik knew was that the bees were behaving strangely—some stumbling in circles, others already dead—and that they would make a great meal for his praying mantis. “She was hungry,” recalls Hafernik. A few days later, Hafernik found more bees, and again fed them to the mantis.

While Hafernik’s bees were few in number, they fit the pattern of colony collapse, because they were wandering around at night, when they’re supposed to be warm and cozy in their hives. One night, he collected a bunch of the bees in a vial and forgot about them. He found the vial a week later, filled with dead bees—along with a batch of baby bugs.

“I knew the bees had been parasitized,” Hafernik said. “By a fly.”

Parasites aren’t an unusual phenomenon, of course, and when Hafernik did the requisite testing to determine what particular type of fly this was—Apocephalus borealis, a parasitic little beast first described in Maine in 1924—he understood right away why his praying mantis’s food was acting so odd. The Apocehalus borealis—or “zombie fly,” as Hafernik has taken to calling them—makes its way in the world by landing on the abdomen of its victim, sticking a hypodermic needle-style “ovipositer” into the softest spot, and depositing a number of eggs there. The eggs hatch, feed on the unsuspecting insect’s tissue, and, ultimately, turn it into a zombie.

ZomBee, rather.

Until Hafernik and his late-night discovery, though, no one knew the Apocehalus borealis were zombifying bees. Infected honeybees that should be sleeping at night instead ramble out into the darkness, where their fate is sealed. “Flight of the living dead,” Hafernik calls it.

Once the bee dies, maggots eat the carcass, turn into zombie flies, and buzz off in search of their next host. Another impending sign of the zombie apocalypse? Hard to say. Mother nature is actually chock-full of zombies and mummies, from the mummy berries blighting blueberry farmers across the Pacific Northwest over the past few years, to the creepy “parasitic wasp” known as Hymenoepimecis argyraphaga that lays eggs in the abdomen of the “spooked spider,”Plesiometa argyra. Those eggs somehow convince the spider to spin a completely aberrant kind of web that then provides a cocoon for the wasp’s larvae, which are all the while munching on the poor spider’s insides as she constructs their new living quarters.

The reason these ZomBees have piqued Hafernik’s curiosity is because this appears to be a relatively new phenomenon, one timed with another scary and poorly understood phenomenon, Colony Collapse Disorder. There’s a host of suspects behind the disorder: mites, viruses, malnutrition, pesticides, genetic homogeneity, and stress. But ZomBees haven’t, up to this point, been added to that list of suspects. Hafernik says it may be time to expand the variables.

“It’s not good news for the bee,” Hafernik said. “I’m trying to get more information to find out how widespread the phenomenon is, and find out how intensive the effect is on beehives. We’re trying to figure out whether the fly is a leading actor in all this, or a bit player in a B movie.”

To that end, Hafernik has established a “citizen science” website, which includes a map of the U.S. and red markers to denote where ZomBees have been found. In the four years since Hafernik first stumbled upon those stumbling bees in San Francisco, others have documented ZomBees in South Dakota, Washington State, and, just last month, Oregon.

Once the bee dies, maggots eat the carcass, turn into zombie flies, and buzz off in search of their next host.

The zombie fly has been found all over North America, from Alaska to New Mexico, up and down the eastern seaboard and in Alberta and Ontario, Canada. But what’s unclear is whether they’ve been monsterfying honeybees all this time, unnoticed, or whether this is a new trick, a new threat to a critical species.

Oregon State University honeybee specialist Ramesh Sagili reported the state’s first ZomBee in early September, but he said he doubts the zombie fly poses any real threat to the species—at least, beyond the threat that’s already known.

That’s because the reports of ZomBees are so far relatively small, Sagili said in a release posted to the university’s website. “I don’t think it’s at the level where it can depopulate hives in large numbers,” he said.

Sagili believes that the zombie fly is just getting creative, that it’s, perhaps, finding new hosts because the ones upon which it normally relies aren’t as available, for some reason. It’s also possible that scientists haven’t noticed ZomBees before because those collected are usually preserved in alcohol, which would kill the larvae before they get a chance to emerge.

Time—and perhaps John Hafernik’s growing legion of ZomBee watchers—will tell if Sagili is right, or if the insect apocalypse truly is nigh.