"They basically eat the insides out of the bee," said San Francisco State University biologist John Hafernik.
About a week later, he had evidence his bees were infected: the pupae of parasitic flies. They were the first to be confirmed in Washington State, The Seattle Times reported.
The researchers found that parasitized bees in the wild abandon their hives and congregate near light sources, where they begin to behave strangely. A bee near death typically will sit in one place and curl up, but these infected bees walked around in circles, appearing disoriented and with little equilibrium, often not being able to stand up.
It's currently unclear how the flies are changing the bees' behavior, though the researchers hypothesize that the flies somehow affect the bees' circadian rhythm, or natural day/night cycle. The researchers also don't know whether infected bees are leaving the hive to protect other bees, or whether hive mates sense the infection and force the dying bees out.