ear-worm (n.)

1880, "boll-worm, corn parasite" (corn-ear-worm attested from 1855), from ear (n.2) + worm (n.). Also an old alternative name for "earwig" (from ear (n.1)); from 1881 as "secret counselor." From 1989 as "annoyingly unforgettable pop song or part of a song."