If you enjoy watching butterflies in your garden there are ways you can encourage them to visit. Butterflies have a three stage life cycle starting as caterpillars which change into a pupa from which the butterflies finally emerge. Each stage involves different plants, but there are many common flowers that will attract adult butterflies. I found an article by John Shaffer on The Master Gardeners website which gives specific suggestions on plants you should grow.

Butterfly gardens are a great source of enjoyment. They can extend to interest youth in nature by providing a small window of native inhabitants of the local environment.
First, let?s look at the life cycle and basic anatomy of a butterfly. Butterflies begin their life as an egg, laid either singly or in clusters depending on the species. Tiny caterpillars emerge and, after consuming their eggshell, they feeding on host plants. Caterpillars must crawl out of their skin or molt, usually around five times, before changing into a pupa. Finally, an adult butterfly emerges, spreads its wings and flies away. This type of development is complete metamorphosis.
Adult butterflies and moths have mouthparts shaped into a long, coiled tube. Forcing blood into the tube straightens it out, allowing butterflies to feed on liquids. Butterflies get all their food from this tube, which limits them to nectar and standing water. Larvae, on the other hand, have chewing mouthparts that they use to skeletonize or totally defoliate leaves. Butterflies have large, rounded compound eyes that allow them to see in all directions without turning their head. Like most insects, butterflies are very nearsighted, and are more attracted to large stands of a particular flower than those planted singly. They see polarized light (which tells the direction the sun is pointing) as well as ultraviolet light, which are present on many flowers and guide them to nectar sources. Butterflies also have a very well developed sense of smell from their antennae. All butterflies’ antennae are club-shaped, as opposed to moths, which can be many shapes but often are feathery.

Different species of butterflies have different preferences of nectar, in both colors and tastes. A wide variety of food plants will give the greatest diversity of visitors. Try staggering wild and cultivated plants, as well as blooming times of the day and year. Groups of the same plants will be easier for butterflies to see than singly planted flowers.
Some varieties of flowers will be more attractive to many species of butterflies. The list of butterfly attracting plants is endless. Some plants that are easily grown in Zone 6 include, but are not limited to: Bee Balm, Black-eyed Susan, Blue Mist Shrub, Egyptian Star-Cluster, Garden Phlox, Hyssop, Joe-Pye Weed, Purple Coneflower, Swamp Alyssum Sweet Alyssum, Zinnias and a myriad of others.

See more at The Master Gardeners