Critter targeting macro help

[Whiplash73]

I'm sure someone may have thought of this, but I'm tryign to put together a macro to target critters for the "Critter Kill Squad" achievement on my hunter.

Does anyone know of a way to target "critters", i..e rats, roaches, sheep, etc. by their class or subgroup, as opposed to listing each npc individually in a /target list?

any help would be appreciated.