You shouldn't have to feed them unless there is no algae or biofilm visible in the tank for them to eat. And if you have plants they'll probably turn their attention to them if they get super hungry, which would be a good indicator to feed them.
Good luck trying to keep them from eating any food you add to the tank! haha
Like others have suggested, they won't need much supplemental feeding in a well-established tank with other inhabitants. But I feed mine (intentionally) occasionally and the rest of the time, they eat whatever their tank mates are having if they can get to it.