A corruption of the Saxon ear-wicga (ear-insect); so
called because the hind wings resemble in shape the human ear. The word
has engendered the notion that these insects are apt to get into our
ears.
An earwig,
metaphorically, is one who whispers into our ears all the news and
scandal going, in order to curry favour; a flatterer.
“Court earwigs banish from your ears.” Political Ballads.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894