Something strange has been happening in Eastern Colorado at night.
Since the week of Christmas, giant drones measuring up to six feet across have been spotted in the sky at night, sometimes in swarms as large as 30. The Denver Post first reported these mysterious drone sightings in Northeast Colorado on Dec. 23, 2019. Since then, sightings have spanned six counties across Colorado and Nebraska.
Phillips County Sheriff Thomas Elliot had no answer for where the drones come from or who they belong to, but he has a rough grasp on their flying habits. “They’ve been doing a grid search, a grid pattern,” he told the Denver Post. “They fly one square and then they fly another square.”
The drones, estimated to have six-foot wingspans, have been flying over Phillips and Yuma counties every night for about the last week, Elliott said. Each night, at least 17 drones appear at around 7:00 pm and disappear at around 10:00 pm, staying 200-300 feet in the air.
The Federal Aviation Agency told the Post it had no idea where the drones came from. Spokespeople for the Air Force, Drug Enforcement Administration, and US Army Forces Command all said that the drones did not belong to their organizations.
As the airspace in which the drones are flying is relatively ungoverned, there are no regulations requiring the drone operators to identify themselves. However, Elliott said that the drones do not appear to be malicious.
The Post spoke to commercial photographer and drone pilot Vic Moss, who said that the drones appear to be searching or mapping out the area. Moss said that drones often fly at night for crop examination purposes. It’s also possible that the drones belong to one of several drone companies based in Colorado, which may be testing out new technologies.
In the meantime, Moss urges residents not to shoot down the drones as they are highly flammable.
“It becomes a self-generating fire that burns until it burns itself out,” he told the Post. “If you shoot a drone down over your house and it lands on your house, you might not have a house in 45 minutes.”
This article originally appeared on Business Insider. Follow @BusinessInsider on Twitter.