In autumn I often see round vertical spider webs without a spider in them. Perhaps they’re the webs of marbled orb weavers.
If the spider was there, you’d see that it’s only 9-22 mm (.3 to .8 inches) long. Males are the typical spider shape but the females have large, round, marbled abdomens ranging in color from orange to yellow with purple markings and pale spots.
“Marbled orb weaver” describes them perfectly. They’re also called “pumpkin spiders” for obvious reasons.
I’ve rarely seen the marbled female and here’s why: After she spins her web she attaches a signal thread to the center and retreats to a hiding place where she holds the thread while she waits. The signal lets her know when something hits the web and out she comes.
Where does the spider hide? The Capital Naturalist tells us in this video.
(photos from Wikimedia Commons; click on the captions to see the originals. video by the Capital Naturalist)