On September 9, 1947, a team working on the Harvard Mark II computer in Cambridge, Massachusetts, found a moth wedged between the contacts of relay #70 in panel F. The insect had shorted out the relay and was causing the machine to malfunction. Once the operators fished it out, someone taped the moth directly into the computer’s logbook and wrote beside it: “First actual case of bug being found.”
The word “bug” for a mechanical or electrical fault actually predates this by decades — Thomas Edison used it in his notebooks back in the 1870s. But the Mark II moth is the moment the term got a literal, physical punchline, and it’s widely credited with popularizing “debugging” as the word for tracking down and fixing the problem. Grace Hopper, the pioneering programmer and future Navy rear admiral who was part of the Mark II team, wasn’t the one who taped in the moth, but she loved the story and told it often in her lectures for years afterward, which helped cement it in computing folklore. The actual logbook page, moth and all, now lives in the Smithsonian’s National Museum of American History.
It’s a fitting bit of trivia for an industry that still spends a huge share of its time hunting down bugs, just ones made of code instead of insect wings. Next time you’re staring down a stack trace, you can take small comfort in knowing engineers have been “debugging” machines for nearly 80 years — moth included.
Source: Computer History Museum
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