One Of The First "Computer Bugs" Was A Bug – Literally

The story involves the only (perhaps) mathematician to have a warship named after them


Tom Hale

Senior Journalist

clockJul 29 2022, 08:35 UTC
The First "Computer Bug" Moth cellotaped to a log book after becoming trapped between points at Relay # 70, Panel F, of the Mark II Aiken Relay Calculator while it was being tested at Harvard University,
Behold, the world's first computer bug. Image credit: Naval Surface Warfare Center, Dahlgren, VA./US Naval Historical Center Online Library Photograph/Wikimedia Commons/Public Domain

It’s an oft-touted snippet of cyber folklore that the first computer bug was literally a bug. A squashed moth, to be precise. Like many anecdotes that find their way into modern legend, it appears that this story was founded in truth, but some re-tellings of the tale may have got the details a bit muddled. 

Here’s how the story goes, according to scholar Fred R Shapiro: On September 9, 1945 (some sources say 1947), Harvard engineers were working on the Mark II, also known as the Aiken Relay Calculator, an electromechanical computer that was being tested for the US Navy. 


One of the bright sparks working on this project was Grace Hopper, a trail-blazing computer pioneer and US Navy rear admiral who holds the exceptionally rare honor of being a mathematician who has a warship named after them.

The team of computer scientists noticed that Mark II was playing up. After taking a look at the hardware, they saw that the glitch was being caused by an unfortunate moth that had become sandwiched in between relay 70 of panel F.

The frazzled moth was removed and Cooper placed the specimen into the day’s log sheet using some sticky-taped along with the notation: “First actual case of a bug being found.”


In 1988, the log book was rediscovered at the Naval Surface Warfare Center Computer Museum in Virginia and the moth was still taped to the sheet, perhaps a little dusty but otherwise fine. 

This part of the story seems to be true. At least, there’s no reason to assume it was made up. However, some interpretations of the story go one further and suggest the term “computer bug” was directly derived from this incident. This certainly isn’t the case. 

The term “bug” was used by none other than Thomas Edison as far back as 1878 when he was writing to fellow inventor Theodore Puskas. His letter reportedly reads: “Bugs – as such little faults and difficulties are called – show themselves and months of intense watching, study and labor are requisite before commercial success or failure is certainly reached.”


Similarly, Shapiro writes that the Supplement to the Oxford English Dictionary defines the noun “bug” as “a defect or fault in a machine, plan, or the like.” The dictionary definition cites a newspaper from 1889 that says: “Mr Edison… had been up the two previous nights discovering a ‘bug’ in his phonograph—an expression for solving a difficulty, and implying that some imaginary insect had secreted itself inside and is causing all the trouble.”

So, it appears that the word “bug” has been used to describe an unexpected hiccup, especially regarding machinery or electronics, for over half a century before the infamous case of the Mark II computer. 

It's also impossible to say whether this anecdote could be considered the first computer bug. Certainly, computers were very much in their infancy in the 1940s, but there's no telling whether this glitch was the first time a computer error had been called a bug. 


Nevertheless, few would argue that the legend of the crushed moth isn't a great story that deserves retelling, wherever the exact truth lies. 

[H/T: Victtor Ciferri on Twitter]

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