The meaning 'defect in a machine' (1889) may have been coined c.

A similar application of the word signifying an object dread to creeping things is very common. The name of bug is given in a secondary sense to insects considered as an object of disgust and horror, and in modern English is appropriated to the noisome inhabitants of our beds, but in America is used as the general appellation of the beetle tribe.

Middle English Compendium compares Low German bögge, böggel-mann 'goblin.' The sense shift perhaps was by influence of Old English -budda, used in compounds for 'beetle' (compare Low German budde 'louse, grub,' Middle Low German buddech 'thick, swollen'). Some speculate that these words are from a root meaning 'goat' (see buck (n.1)) and represent originally a goat-like specter. The Middle English word probably is connected with Scottish bogill 'goblin, bugbear,' or obsolete Welsh bwg 'ghost, goblin' (compare Welsh bwgwl 'threat,' earlier 'fear,' Middle Irish bocanách 'supernatural being'). 'insect, beetle,' 1620s (earliest reference is to bedbugs), of unknown origin, probably (but not certainly) from or influenced by Middle English bugge 'something frightening, scarecrow' (late 14c.), a word or meaning that has become obsolete since the 'insect' sense arose, except in bugbear (1570s) and bugaboo (q.v.).

Doodlebug definition