Do frogs eat the common blue butterfly?

yes.

there is a wild frog that lives in my front garden. in the summer nights when there are about 50 fireflies flying around my front lawn, i catch some in my hand, and lay them in front of the frog. be sure to squeeze the fireflies a little bit after you catch them, so they dont fly away right after you put them down. but make sure their still alive. my frog usually just sits there, then notices the fly start crawling, then in one quick motion extends his tongue out and the fly is gone!! have fun!!