The butterfly has been in Creatures 1, 2, and 3, in many different forms. In C1, the Cloud Layer Butterfly was featured in the second object pack for the game.
The Creatures 2 Purple Butterfly has an edible caterpillar.
Helen created both the Enchanted Butterfly and the Sugar Butterfly for C2. Many other kinds of butterflies are up for download on numerous sites.
Official Ecology image