These things get on my Canna's every year and cut pieces of the leaves and turn them over, sticking them together and hiding inside. I don't know if they actually eat the leaves or just use them as a home. I have hesitated killing them because I don't know what they are or if they turn into something good (better than a slimy slug that cuts my leaves!) - like tomato worms turn into beautiful hawk-moths. Does anyone know what this is and if it turns into something in another life?
Those are leaf rollers, a pain for canna growers! As far as I know, they aren't good for anything except food for birds! Sprinkle some Dipel around the cannas to kill them.
They do make a plain brownish butterfly that lays more eggs to eat more holes in your cannas.