古英語のbugge(悪魔、恐れるべきもの)から。後に昆虫を指すようになった。bugの意味は、偉大な発明家トーマス?エジソンが故障した機械を調べているうちに、中で死んだ小さな虫が原因であることを発見したことに由来すると言われている。
In the United States bug is not confined, as in England, to the domestic pest, but is applied to all insects of the Coleoptera order, which includes what in this country are generally called beetles. [Farmer & Henley, "Dictionary of Slang and Colloquial English," 1912 abridged edition]Meaning "defect in a machine" (1889) may have been coined c. 1878 by Thomas Edison (perhaps with the notion of an insect getting into the works). Meaning "person obsessed by an idea" (such as firebug) is from 1841, perhaps from notion of persistence. Sense of "microbe, germ" is from 1919. Bugs "crazy" is from c. 1900. Bug juice as a slang name for drink is from 1869, originally "bad whiskey." The 1811 slang dictionary has bug-hunter "an upholsterer." Bug-word "word or words meant to irritate and vex" is from 1560s.