The first ever computer bug was literally a real bug.
The story goes that Grace Hopper (who later became the first lady Admiral of the U.S. Navy) was working on the Mark II computer. The computer was malfunctioning and when she looked inside the machine they found that a moth had shorted some electronics out. So there was a bug in their system. And when they De-bugged the system - it started working again. Grace removed the moth and tapped it to her log book. (Which can now be seen at the Smithsonian).