vermin (n.)

c. 1300, "noxious animals," from Anglo-French and Old French vermin "moth, worm, mite," in plural "troublesome creatures" (12c.), from Vulgar Latin *verminum "vermin," possibly including bothersome insects, collective noun formed from Latin vermis "worm" (from PIE root *wer- (2) "to turn, bend"). Extended to "low, obnoxious people" by 1560s.