The Moth in Grace Hopper's Logbook

On September 9, 1947, operators at Harvard's Computation Laboratory pulled a moth out of relay 70, panel F, of the Mark II Aiken Relay Calculator. They taped it into the daily logbook with the note: "First actual case of bug being found." The page now lives in the Smithsonian's National Museum of American History.

Grace Hopper liked telling the story. She was on the Mark II team and helped popularize it for decades, but she was careful to say she did not personally find the moth — and the joke in that logbook entry only lands because the operators already used "bug" as engineering slang for a defect. Thomas Edison was complaining about "bugs" in his telegraph and phonograph designs as early as 1878, in letters that survive in the Rutgers Edison Papers archive.

The Mark II moth is a coincidence the team noticed and immortalized. The wording — first actual case — is the giveaway: they thought it was funny precisely because the metaphor had been kicking around for almost seventy years and now, finally, somebody had a literal one to scrape out of a relay.