US scientists have discovered that a fly parasite can turn honey bees into confused zombies before killing them, in an advance that could offer new clues to why bee colonies are collapsing. So far, the parasite has only been detected in honey bees in California and South Dakota, American researchers reported in the open access science journal PLoS ONE this week. But if it turns out to be an emerging parasite, that \"underlines the danger that could threaten honey bee colonies throughout North America,\" said the study led by San Francisco State University professor of biology John Hafernik. Hafernik made the discovery by accident, when he foraged some bees from outside a light fixture at the university to feed to a praying mantis he\'d brought back from a field trip. \"But being an absent-minded professor, I left them in a vial on my desk and forgot about them. Then the next time I looked at the vial, there were all these fly pupae surrounding the bees,\" he said. Soon, the bees began to die, but not in the usual way by sitting still and curling up. These bees kept trying to move their legs and get around, but they were too weak, said lead author Andrew Core, a graduate student in Hafernik\'s lab. \"They kept stretching them out and then falling over,\" said Core. \"It really painted a picture of something like a zombie.\" Further study showed that bees that left their hives at night were most likely to become infected with the fly parasite, identified as Apocephalus borealis. Once bees were parasitized by the fly, they would abandon their hives and congregate near lights, a very unusual behavior for bees. \"When we observed the bees for some time -- the ones that were alive -- we found that they walked around in circles, often with no sense of direction,\" said Core. The parasite lays its eggs in the bee\'s abdomen. About a week after the bee dies, the fly larvae push their way into the world, often exiting from between the bee\'s head and mid-section. The research, which has also confirmed that the same flies have been parasitizing bumblebees, won local excellence awards when it was first presented last year. Next, the team hopes to find out more about where the parasitization is taking place, and whether the \"zombie bees\" leave the colony of their own accord or if their disease is sensed by comrades who then push them out. Researchers plan to use tiny radio tags and video monitoring to find clues to the mystery. \"We don\'t know the best way to stop parasitization, because one of the big things we\'re missing is where the flies are parasitizing the bees,\" Hafernik said. \"We assume it\'s while the bees are out foraging, because we don\'t see the flies hanging around the bee hives. But it\'s still a bit of a black hole in terms of where it\'s actually happening.\" Experts have theorized that the huge die-off of bees worldwide since 2006, a major threat to crops that depend on the honey-making insects for pollination, is not due to any one single factor. Parasites, viral and bacterial infections, pesticides, and poor nutrition resulting from the impact of human activities on the environment have all played a role in the decline. The mysterious decimation of bee populations in the United States, Europe, Japan and elsewhere in recent years threatens agricultural production worth tens of billions of dollars.