Long, floating spider webs are bobbing through the skies of Northern California this week. And they’re confusing some community members concerned about biological weapons, UFOs and other phenomena.

The gossamer-thin, shimmery “sky webs” are between 18 inches and several feet long. They’ve been seen drifting through the sky and catching on fences and trees.

The webs come from young spiders that launch themselves on their homemade parachutes after hatching to be blown to a new home.