if you have aggressive fish then butterflies will might be an idea but if community then peppermints would eat them...hopefully. my dads tank was over ridden with them and he tried for a long time to get rid of them until he did what worked great. he took out his rock and put them in a tub filled with water that was a drastic salinity. from 1.023 to 1.012. left them in there for 2 days. then put them back into the tank. obviously u'll have some die off on the rock, but it was worth it to him since he had been trying to get rid of them for a long time.