Ignoring all the things I should be doing this afternoon, I went to the web in quest of the answer to this question.

When I went to the site for The Lepidopterists' Society,
I saw that one of the committee members who established their rules for collecting lives right here in Louisville.
(This is an international committee.)

So I called him! He said, "There is none". No official group name, though if many are flying together, they are sometimes called a migration.