The First Computer Bug Was a Real Moth

Every developer who has ever muttered "there is a bug in this" is repeating a word with a surprisingly literal origin. On September 9, 1947, the operators of the Harvard Mark II, an early electromechanical computer, traced a malfunction to its source and found something they did not expect: a moth wedged inside Relay #70. They removed the insect, taped it into the operations logbook, and wrote a now-famous line beside it: "First actual case of bug being found." That page, moth and all, survives today in the collection of the Smithsonian's National Museum of American History. It is one of the best-loved stories in computing, and like most good stories it is a little more complicated than the popular version. Worth getting right, because the discipline it gave us is the same one behind every connected device we build. What actually happened in 1947 The Mark II was a room-sized machine built from relays, switches, and thousands of moving parts. When a moth flew into one of those relays, it physically interfered with the contacts and caused a fault. The technicians who found it had a sense of humor: calling it the "first actual case of bug being found" was a joke precisely because engineers had already been using "bug" for years to describe mysterious faults in machinery. Thomas Edison used the term in his notebooks back in the 1870s. So the 1947 moth did not invent the word "bug." What it did was give the term a perfect, photographable origin story, and it cemented the companion word that really matters: debugging. The act of removing that moth was, quite literally, de-bugging the computer. The Grace Hopper connection The story is almost always told with Grace Hopper at its center, and that deserves a small correction. Hopper, a pioneering computer scientist who later helped develop COBOL, was part of the Mark II team in 1947, but the evidence suggests she did not personally find the moth or write the logbook entry. What she did do was tell the story, brilliantly and o