I've seen moths come through in big clouds like that, but never butterflies. Would have been something to see.
I like Painted Lady butterflies. When I was teaching, classes often got cocoons of them for life cycle studies and then released them once they were out. One year, early in the days of using the internet, my friend who was teaching Grade 3 decided to do some computer research on them with her class. She got the kids all in the computer lab, and had them put "Painted Ladies" in the search box on their screens. They were probably searching Images. An inappropriate for 8 year olds and totally different kind of "painted lady" came up on the screen! Ha ha, we all learned something about using really specific search terms after that.