On September 9, 1947, engineers at Harvard University weren’t chasing a glitch in their code — they were chasing an actual insect. The Harvard Mark II, a room-sized electromechanical computer, kept failing, and nobody could figure out why.

The culprit turned out to be a moth. It had flown into Panel F, relay #70, and gotten zapped between the contacts, jamming the mechanism. Operator Grace Hopper’s team fished it out with tweezers, taped it into the machine’s logbook, and wrote beneath it: “First actual case of bug being found.”

Here’s the twist: the word “bug” for a technical fault already existed — Thomas Edison used it in his notes as early as 1878. What the Harvard team actually did was make the word literal, and give the world its favorite piece of computing folklore in the process.

That taped-in moth still survives today, preserved at the Smithsonian’s National Museum of American History — a 1940s pest control problem immortalized as tech history’s most famous debugging story.