Adult butterflies never excrete waste, they use up all they ingest for energy.
Picture from Texas Butterfly Ranch
As adults, butterflies consume only liquids. They sip water from damp patches for hydration and then feed on nectar from flowers, which is where they obtain sugars for energy as well as sodium and other minerals necessary for reproduction.
Many adult butterflies never excrete waste—they use up all they eat for energy - See more at: http://animals.sandiegozoo.org/animals/butterfly#sthash.MYcOKS6Y.dpuf