If you have the resources, make a Power Point, or a Prezi. Or find and edit a Smartboard lesson. Or find a Prezi. Or find several really good books about butterflies - they'll love a "true/false" book, with facts like, "True or False, can butterflies taste their food with their feet?" [true fact].
And if you're in the first grade, make a life cycle. On a paper plate.
Orzo for your egg. Some kind of rotini for your larva/caterpillar. Mini shell pasta for the chrysalis/pupa. And Farfalle. Which, in Italian, literally means "butterfly". So you're not eating "bow-tie" pasta, you're eating "butterfly" pasta.
And if you're the student teacher in charge, pre-mark the paper plates with Sharpie quarters. Trust me.