Redbugs generally stay on acropora.They irritate the polyps,which makes them slime..they eat the slime.This in turn makes the polyps retract,the coral loses color or bleaches..and can die.The only critter I know of that eats redbugs is a dragonface pipefish,but they are very difficult to keep,requiring live food...like mandarins,scooters,seahorses,etc.The only current way to rid your tank of redbugs is interceptor..and it does kill most inverts.