In 1947, engineers operating Harvard’s electromechanical Mark II computer traced a malfunction to a moth lodged in one of its relays. They removed the insect, taped it onto the day’s logbook page, and wrote that it was the “first actual case of bug being found.” The physical page turned a familiar technical metaphor into an irresistible specimen.

The moth did not invent the word. Engineers had used “bug” for faults or interference in electrical systems since the 1800s, and “debug” also existed before the Mark II incident. The joke depends on that older vocabulary: this time the trouble in the machine really did have wings. The Mark II team helped carry both terms into the emerging culture of computer programming.

Grace Hopper worked with the Harvard computing group and later recounted the story, which is why the insect is often credited directly to her. The Smithsonian notes that the logbook probably was not Hopper’s personal book, and the surviving page does not establish that she found or taped the moth herself. She belongs in the larger history of the team and the language it popularized. The artifact now held by the National Museum of American History preserves folklore with its evidence still attached.