The best replacement for bug is insect.

The best alternatives to bug are rated as following:
★★★★★  insect
★★  defect
★★  food poisoning
★★  feature
★★  cockroach
★★  beetle
★  bug
★  flu
★  flea bites
★  tick
★  spider bite
★  glitch
★  fighting
★  spider bites
★  grass pokemon
  gribble
  insect difference
  wood louse
  biker
  go wear fit
  flea
  mosquito bite
  morning sickness
  asian beetle
  roach
  issue
  error
  pregnant
  firefly
  bed bug
  badger
  enhancement
  hummingbird
  chigger
  rootsman
  bat bug
  jerusalem cricket
  roaches

Your alternative for bug is not listed? Suggest!
Speaking about bug, one probably shouldn't forget about hard shell.

Other search terms related to bug and their ratings are:
★★★★★ hard shell
★ black and red
You have in mind a companion for bug and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of bug in all years. Click on graph for more.
bug
insect
defect