Is it true that it once rained cobwebs?

Yes. The Great Cobweb Storm of October 1881 was observed from Milwaukee to Sheboygan, Wisconsin, along the western shore of Lake Michigan. This event was caused not by rainfall, but by the migratory habits of certain species of spiders, which cast their silk on a breeze and tag along for the ride as the wind bears them away. Observers saw strong white strands, which varied greatly in size from mere specks to 60 feet in length and which filled the sky thickly as high as the eye could see.