What age group is this costume for?
Preschool and Younger
Elementary School
Middle School
High School & Beyond

Estimated time required to make this costume:
1-1 1/2 Hours (and maybe a Wal-Mart Trip)

Difficulty level:
Almost as easy - some sewing

Items you will need: (Hit your return key to start a new line)
A simple, solid-colored floor-length dress

A pair of elbow-length gloves (preferably the same color as the dress)

Two large pieces of fabric (about 1X1 yards each; a gauzy material works best)

A piece of ribbon about 2 ft. long

Sequins (optional)

Instructions:
Cut the two pieces of fabric in the shape of butterfly wings. Be sure to make them about the same size so your butterfly won't look too weird.
Sew a wing onto each glove so that they hang down (cutting the hands off of the gloves is optional, depending on what look you like best).
Sew the wings together at the top so that when you spread them out you have a butterfly shape.
Sew (or hot glue) the center of the ribbon to the same spot where you sewed the wings together so that you can put the gloves on and tie the ribbon around your neck, creating the perfect butterfly.
Highlighting the wings with the sequins is optional, depending on how much time you have used.
Wear your wings over the solid-colored dress for a perfect butterfly look!

Other information to consider:
This also works for angels if you use white.