While driving across the upper Klamath Basin mid October, my husband and I saw what looked like spider silk or web drifting in the air, and caught in trees and fence-lines - lots of it! Can you tell me what that is?
Well, it could very well have been spider silk that you were seeing. In certain species, baby spiders will spin a silk strand as a "balloon" to float on the wind as a means of dispersal. Depending on the species, this happens in the fall or spring. When "all of the stars" align — the right time of year, right weather conditions, right angle with sunlight — there can be conspicuous amounts of these silk balloons to see. This article from National Geographic describes a particularly massive occurrence.
Even when it's not so apparent, the spiders are still out there. This picture is one I took at our research station this morning after receiving your question. There are a couple of balloons flapping across the bed of that pickup. This morning is sunny and breezy after several rainy days, so maybe it's a good day to fly.