Was the first computer bug really a moth?

Yes and no. A real moth really did jam an early computer, but it was not the origin of the word bug. Engineers had been calling defects bugs since at least the 1870s. In 1878 Thomas Edison wrote about the little faults and difficulties in his inventions and called them Bugs.

The moth story is still true. On 9 September 1947, operators of the Harvard Mark II, a room-filling electromechanical computer built with relays, traced an error to a moth trapped in one of those relays. They removed it and taped it into the machine's log book with the note: First actual case of bug being found.

The key word is actual. The operators already knew the engineering slang, and they were almost certainly making a pun, enjoying the fact that for once the bug was a real insect. Their joke is actually evidence that the word was already common in computing at the time.

The story became famous thanks to Grace Hopper, a Navy officer, mathematician and computer pioneer who was working on the Mark II at Harvard and popularized it. Hopper later helped create COBOL, one of the first high-level programming languages. The log book, moth still attached, now sits in the Smithsonian National Museum of American History. So the next time software misbehaves, you can blame a very old word, and one very unlucky moth.