The word “bug” originally had nothing to do with insects. It started as a Middle English word, “bugge,” meaning a hobgoblin or frightening specter. Over centuries it drifted from ghosts to creepy-crawlies to software glitches, picking up new meanings at every stop. How it made that journey is a surprisingly entertaining story about language, bedbugs, and Thomas Edison.
From Ghosts to Creepy-Crawlies
In the 1300s and 1400s, “bugge” referred to something supernatural and frightening. One of its earliest appearances is in a 14th-century English Bible translation, where it described either a hobgoblin or a scarecrow: “a bugge, either a man of raggis, in a place where gourdis wexen.” The word carried a sense of dread, something lurking and unwelcome. This is also where we get “bugbear” and “bugaboo,” both terms for imaginary monsters meant to scare children.
Sometime around the 1600s, English speakers started applying “bug” to small creatures that provoked a similar reaction: disgust, unease, the feeling of something crawling where it shouldn’t be. The bedbug was likely the bridge between meanings. Bedbugs are blood-sucking parasites that emerge at night, hide in crevices, and torment sleepers. It’s easy to see how a word meaning “terrifying thing in the dark” got attached to an actual terrifying thing in the dark. Notably, the bedbug (Cimex lectularius) is one of only a handful of insect species that feeds almost exclusively on humans, and researchers have pointed out that no Native American language had a word for bedbug, suggesting the pest followed European settlers to the New World.
What Scientists Mean by “Bug”
Entomologists use “bug” in a much narrower way than the rest of us. In scientific terms, a true bug is an insect in the order Hemiptera, suborder Heteroptera. These insects share a specific feature: piercing-sucking mouthparts, essentially a needle-like beak they use to puncture surfaces and suck out fluids, whether plant sap, other insects’ insides, or blood. The order’s name comes from Greek (hemi meaning half, pteron meaning wing) and describes their distinctive forewings, which are thickened and leathery near the body but thin and membranous at the tips.
Stink bugs, assassin bugs, water striders, backswimmers, lace bugs, and bedbugs are all true bugs. Ladybugs, despite the name, are beetles. Pillbugs are crustaceans. Spiders are arachnids. Lightning bugs are beetles too. The casual use of “bug” for anything small and crawling drives entomologists slightly crazy, but it’s been going on for centuries and shows no sign of stopping.
How “Bug” Jumped to Technology
Most people credit Grace Hopper and a moth found inside Harvard’s Mark II computer in 1947 for giving us the tech meaning of “bug.” The story is real (the moth is preserved in the Smithsonian), but the term was already decades old by then. Thomas Edison was using “bug” to describe technical glitches as early as the 1870s.
The term first appeared in Edison’s notebooks in 1876, during experiments with multiplexing telegraph signals. By 1878, he was using it playfully in letters to colleagues. He wrote to Western Union’s president that he’d found “a bug” in his apparatus, joking that it was “of the genus ‘callbellum'” and that “the insect appears to find conditions for its existence in all call apparatus of Telephones.” Later that year, he described to an associate what happens after conceiving an invention: “‘Bugs,’ as such little faults and difficulties are called, show themselves, and months of anxious watching, study, and labor are requisite before commercial success, or failure, is certainly reached.”
Edison and his team even used the verb form. His “insomnia squad” of engineers would stay up all night “debugging” his inventions. By 1888, telegraph operators widely recognized the term. William Maver, who wrote the standard book on American telegraphy, noted that those familiar with Edison’s quadruplex system “are aware that there is tendency in its operation termed, not very elegantly perhaps, the ‘bug.'” A British reporter in 1889 described it as “an expression for solving a difficulty, and implying that some imaginary insect has secreted itself inside and is causing all the trouble.” So when Hopper’s team taped that moth into a logbook decades later, they were riffing on a well-established metaphor, not inventing one.
Why the Casual Meaning Stuck
English is full of words where the scientific definition and the everyday definition parted ways long ago. “Bug” is a perfect example. The general public never had much reason to care about the distinction between Hemiptera and other insect orders, so the word kept its broader, fuzzier meaning: any small creature that crawls, flies, bites, or shows up uninvited in your house. That usage is now so deeply embedded that even entomologists use “bug” casually outside of professional writing.
The word’s emotional core has stayed remarkably consistent across all its meanings. A bugge in 1382 was something unsettling that lurked in the shadows. A bedbug in the 1600s was something unsettling that lurked in your mattress. A bug in Edison’s phonograph was something unsettling that lurked in the wiring. Whether it’s a ghost, an insect, or a line of broken code, a bug is always the small, hidden thing causing problems you can’t quite see.