One of the most popular myths in computing has to do with the origin of the term “computer bug”. As the story goes, one day the ENIAC computer refused to function correctly. The technicians were forced to search through all the miles of wires and relays looking for the cause of the problem. Eventually, the problem was traced to a small moth that had been caught between the electrical contacts of a relay, way back in the machine. The moth was pulled out and promptly taped into the technician’s logbook. “First actual case of bug being found”. From that day on, whenever there was a problem with the machine, the technicians would crawl through the computer looking for bugs.
(Although this is a funy story, the first use of “bug” to mean some type of unexpected mechanical error actually predates the invention of the computer.)
~ From the book “Understanding the Personal Computer”