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.”

“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.)

ZomBee Watch / CityLab

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 todysentery. 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.