Amount of spottage can vary wildly across species. Very common, at least in the northern hemisphere, and very pretty. Fritillary can also be an alternate name for fritillaria, a kind of lily with speckled flowers, but I'm ignoring that sense here except to note that both words come from Latin fritillus, dice-box, for the spots -- though as far as I can tell, it's the dice and not the cup used to store and roll them that typically had the spots. So, no, nothing to do with butterflies being flitty, but I still love the sound connotation.
As he waited for her answer, a fritillary fluttered across the field, passing between them.
Admin note: And with that, I'm going to flit off for a while. Which is to say, I'm about to drop off-line for a few months of paternity leave. While I'm out, brendala will be taking over Thursday posting duties.