I have a decent size (2 inches) Fuji Blue Devil in my 58g reef. Lately I've noticed he's been picking at the back of my Nassarius snails' shells but leaving the larger Astrea snails alone. Is he just picking stuff off their shells or trying to eat them? Anyone else have any experience with this? I know Damsels are a pain in the *** when it comes to other fish but I thought they were generally considered reef safe. TIA