Ok I want the body of the butterfly to look like a bug body so I keep whipstitching til the opening area gets completely covered. You don't want any fabric showing through the black stitches.
Now to add antennae -cut a length of wire that is as long or as short as you want. I like to curl mine so if you want them to curl cut the length at twice of the lenght you want them to end up as.
I cut mine 12" and folded the wire in half.Then I twisted the end a few times to create a circle of wire at the end.
Hold the folded wire up to the black thread as shown in the picture and take a stitch or two through the circle so it will not pull out when it is sewn in.
Then continue to whipstitch over the wire onto the body part until you can't see the wire anymore.
You can find gold craft wire at any craft shop. It is more easily manipulated than a regular wire but you can use any wire you want. The thicker the wire tho the less you will be able to curl it.