Mead Elliott, broadcast facilities manager for the John Hancock Center, said the fall season is a "spider fest" at the top of the building, the Chicago Sun-Times reported Tuesday.
"They are crawling everywhere, they are coming down on their strings everywhere, there are a lot of dead carcasses around -- it's like a haunted house," he said. "It's really weird seeing so many. You scratch your head, literally and figuratively."
Gary Michon, general manager of U.S. Equities Asset Management, the managing agent for the Willis Tower, said running the building's window washing system every day helps control the spider problem at high altitudes.
"It's more of a nuisance to the tenants," Michon said of the spiders. "They are paying for great views; the last thing they want to do is look out their window and see a big web."
Petra Sierwald, associate curator of insects at Chicago's Field Museum, said most spiders reach the high altitudes by letting out a small amount of silk and riding on air currents to the tops of the skyscrapers.