Dec 31, 2012
Zombie fly the latest pest problem for honeybees

The zombie fly, a phorid fly native to North America, is attacking honeybees, said John Hafernik, a professor of biology with San Francisco State University. The fly was previously known to parasitize bumblebees and paper wasps, but attacks on honeybees are a newer development.

The flies infect the bee by laying eggs, which form larvae (maggots) in the bee. The larval infection causes the honeybees to become disoriented and leave the hives at night. Hafernik refers to infected bees as ZomBees. They are attracted to nearby lights, where they become stranded and die, Hafernik said. Once the maggots finish feeding on the dead bee, they exit and form pupae. A single infected honeybee may carry as many as 15 maggots. Two to four weeks later, the adult flies emerge and begin the cycle anew.

The fly is found all over North America, from as far north as Alaska to at least as far south as New Mexico and Georgia, Hafernik said. Regular citizens working with Hafernik’s ZomBee Watch project have expanded the records and geographic extent of the fly.

“We have records of it parasitizing honeybees along the West Coast, from Santa Barbara, California, to Seattle, Washington,” he said. “We also have record from hives in Bakersfield, California, and South Dakota, based on detecting the DNA of the flies in worker bees from those hives.”

Why the infected bees have only been found in these few areas is still under investigation, Hafernik said.

Sampling is taking place across the country and being reported to a website,, set up to inform growers and the general public, as well as track the pest. The ZomBee Watch website is sponsored by the San Francisco State University Department of Biology, the San Francisco State University Center for Computing for Life Sciences and the Natural History Museum of Los Angeles County. It enlists people from all over to report findings and watch for the fly’s effects.

Effects and CCD?

Whether this new pest has had an effect on colony collapse disorder (CCD) is unknown. CCD is believed to be caused by several factors. So far, zombie flies have not been proven to cause hive failures, Hafernik said.

“Being infected with the fly is clearly not a good thing for honeybees, but right now, we don’t know how large an effect the fly has on hive health.”

The presence of fly larvae in up to 18 percent of actively foraging bees in some California hives makes the zombie fly a potential contributor to hive declines. This would be especially likely if zombie fly infection is widespread and higher in areas that are experiencing hive declines, Hafernik said.

“We are not sure at this point how big a problem the fly is for honeybees,” Hafernik said. “We are working to find out if the fly is a major player in honeybee hive losses or only a bit player. The hives that we have worked with are not only infected with the fly, but also with Varroa mites and various bee pathogens, making the picture complicated.”

Except for Western coastal areas, the flies will probably be inactive during winter, Hafernik said.

“We will be making another push to get new samples from across the United States and Canada, starting in May,” he said.

For more information, or to contribute to the search, visit

By Derrek Sigler, Assistant Editor

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P.O. Box 128
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