Tania Robertson, a receptionist at an electrical firm in Bloemfontein, came in to work on Tuesday and spotted the strange sight next to a desk in her office.
The snake, which had obviously died from the spider's poisonous bite, was off the ground and caught up in the web.
Leon Lotz of the arachnology department at the National Museum immediately identified the spider as a female brown button spider.
The brown button spider, easily identifiable by a red hourglass marking on its stomach, is not quite as deadly as a black widow.
He said it was only the second time in South Africa that he had heard of a snake getting caught in a spider's web.
