The first computer bug was a real moth

The story

On September 9, 1947, the Harvard Mark II, one of the early electromechanical computers, kept giving wrong answers. The operators worked through the machine panel by panel until they found the cause: a moth trapped between the contacts of a relay.

They removed it, taped it into the logbook and wrote beside it: “First actual case of bug being found.”

Computer pioneer Grace Hopper, who worked on the Mark II team, loved telling the story, and it helped make “bug” and “debugging” part of everyday computing language. The word itself was older: Thomas Edison used it for technical glitches in the 1870s. The joke in the logbook was that, for once, the bug was literal.

The logbook page, moth still attached, is now in the collection of the Smithsonian’s National Museum of American History.

Why it mattered

The moth gave computing one of its most lasting words. The logbook also showed a habit that still matters: when something goes wrong, someone writes down what they found and how they fixed it, so the next person does not have to start from scratch.

The lesson today

Two habits from that night are still the heart of good IT support.

• Work through the problem methodically. The team did not guess. They checked the machine until the cause showed itself.
• Write it down. Because someone recorded what they found, we still know about it nearly 80 years later. In a business, written notes on what failed and what fixed it save hours the next time something similar happens.