Step 1: Assemble materials and tools.
Scissors to cut straws and string
Computer to print out original butterfly sheet
Copier or copy store to make multiples of sheet.
(Only for at-home version: glue gun)
Transparent tape (not required for at-home glue-gun version)
String (White cotton household string is what I used; kitchen twine is fine; whatever the drugstore down the street from the event has in stock mid-event also turned out to be fine.)
Step 2: Make butterfly
I've uploaded the document as you see it here: one side with 6 butterflies, the other with 6 maps of where in Mexico the monarchs come from.
Copy these onto the thickest cardstock you have access to. If it's too floppy, the toy won't work.
Alternatively, as I did on the prototype, glue the butterfly to a piece of thin cardboard. This worked at home, but would have been an added (unbearable) step at the event.
Cut butterflies apart.