Scientists are reporting that “zombie bees” are popping up in both Western and now Eastern states, and it’s a major threat to essential honey bee populations in the country.

A species of fly, Apocephalus borealis, is laying eggs in the stomachs of bees, which hatch and the maggots then live in the abdomen and control the bee’s behavior, after which it will suddenly die, according to a Design & Trend report.

Now, volunteers are banding together to track this spread of zombie bees under the “ZomBee Watch” project, which was started back in 2012 to document where infestations of Apocephalus borealis were happening.

John Hafernik, who is a biology professor at San Francisco State University and the creator of the project, said that while this is not yet a threat to the existence of honey bees, it is a phenomenon that should be tracked.

In a 2012 paper, Hafernik wrote: “Understanding causes of the hive abandonment behavior we document could explain symptoms associated with CCD. Further, knowledge of this parasite could help prevent its spread into regions of the world where naïve hosts may be easily susceptible to attack.”

Other scientists added that perhaps it’s a bit sensational to refer to them as zombies, honey bee populations are really struggling and a stresser like this is certainly not helpful, according to the report. A total of 40 percent of colonies across the United States have already been lost, and honey bee populations are essential to agriculture as they pollinate plants.

The honey bee refers to any bee that is a member of the Apis genus, and they are basically defined by the fact that they produce and store honey, and build nests from wax. There are seven species of honey bee, and a total of 44 subspecies. This means honey bees make up only a tiny portion of the total species of bees, which numbers at about 20,000 worldwide. Although other bees also sometimes produce honey, only bees from this genus are considered honey bees.