A scarecrow. Bug is the Welsh bwg, a hobgoblin, called in Russia buka. Spenser says, “A ghastly bug doth greatly them affear” (book ii. canto 3); and Hamlet has “bugs and goblins” (v. 2).
“Warwick was a bug that feared us all.”
Shakespeare: 3 Henry IV., v. 3.
To the world no bug bear is so great As want of figure and a small estate.
Pope: Satires, iii. 67-68.
The latter half of this word is somewhat doubtful. The Welsh bár =ire, fury, wrath, whence barog, spiteful, seems probable.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894