The Magic School Bus S03 E03 "Spins A Web"
The class has gone to a drive-in movie to watch the black and white B-film Stand by Your Mantis from 1953 featuring General Araneus (Ed Asner) who is attempting to destroy a giant praying mantis. Carlos and Phoebe are not enjoying it. Carlos hates insects and spiders, and Phoebe is upset and declares that if she were in that movie, then she would trap the mantis, take it somewhere else, and free it. Naturally, this gives Ms. Frizzle an idea. So she drives the bus into the movie. General Araneus takes over the bus, kidnaps Liz, and pushes a button that makes the class go back out of the movie and shrink. He wants to use Liz as bait for the praying mantis. Outside the movie, the class encounter spiders a lot, and when Liz pushes a button that pulls them back in the movie, they apply what they have learned about spiders to stop the General from using Liz as praying mantis bait.