The safety of the spiders was paramount throughout the entire production, so for one scene where McClintock (John Goodman) had to spray an arachnid with insecticide, then squash it with his boot, the production went to extreme measures: first, a dummy spider was sprayed, then Goodman donned special boots with a hollowed out sole for the squash shot, so that the spider would just curl up inside and wait for the next take.
The animatronic General Spider seen at the film's climax was one of the earliest prop jobs done by Jamie Hyneman, star and co-producer of MythBusters - Die Wissensjäger (2003).
Though Jeff Daniels claimed that he was fine with small spiders, he acknowledged that "anyone in his right mind" would have issues with spiders as huge as Big Bob. However, John Goodman wasn't fazed. "I don't have any problem," he said. "We see each other eye to eye; well, two eyes to their 16, but we get along swell."
The small spiders used in the film were Avondale spiders (Delena Cancerides), a harmless species from New Zealand that were provided by Landcare Research in Auckland. Despite their fierce appearance, this spider is a docile member of the crab-spider family and is, in fact, harmless to humans. They were not allowed back in New Zealand for quarantine reasons. The giant "spider" used in the film was a species of a bird-eating tarantula, which can attain a legspan of eight inches or more. Those types of tarantulas are not easy to handle and can give a nasty bite. The spiders in the film were managed and handled by famed entomologist Steven R. Kutcher.
Frank Marshall meant for the film to be like Alfred Hitchcock's Die Vögel (1963), and added, "People like to be scared but laughing, like a roller coaster. No one wants to be terrified." He also made the spider scare more convincing by putting them into the same shot as the actors as much as possible.