Early in the season, I usually start on the warm days in February since the Mourning Cloaks will venture out to nectar, I place smashed bananas, nectarines, pears, watermelon, cantelope, pineapple (this was a surprise when a Snout came to check out the pineapple), even citrus works. Many butterflies use these for nectar even when they are infested with fly larvae. Hackberry and Tawny Emperors, Red Spotted Purples, Red Admirals, Question Marks and Commas, Common Wood Nymphs are a few that I have seen.
What other species have you seen nectaring fruit? Do any of you put out fruit for butterflies?