In Raiders of the Lost Ark, tarantulas crawled over Indiana Jones in the cave.
The scene occurs near the start of the 1981 film, as Indy and his guide Satipo enter the Chachapoyan temple in Peru. A few large tarantulas crawl onto the back of Indy's jacket. Satipo spots them, and Indy calmly brushes them away with his coiled bullwhip.
The joke then reverses the danger: when Satipo turns around, his own back is covered with many more tarantulas. The moment establishes Indy as unusually composed around frightening hazards, while Satipo reacts with understandable alarm. It also helps set the film's pulpy horror-adventure tone before the temple's traps become even more dangerous.
The sequence is often remembered as a general “spider scene,” but tarantulas are the specific animals. The famous snake sequence comes later, in the Well of Souls, where Indy discovers that the chamber containing the Ark is filled with snakes.