When the caterpillars reach their final size they tend to slow down and rest a bit. At this point they need to get rid of any food left in their bodies, and to do so means a purge. After the discharge of stomach contents, the caterpillars will be ready for the next step in life, what I call a walkabout.
The caterpillar will drop off the host plant after purging, (be prepared for a gooey mess beneath the plant) and then travel the area to find a suitable place to form a chrysalis. Don’t worry if the caterpillar climbs several feet up a wall or other tall object. Also, don’t be alarmed if they drop all the way down to the floor from their high perch. My porch is cement, and this terrible drop never seems to even stun the caterpillar. They just go on walking, searching, climbing, and exploring any object in their way.
Finally, they find a spot to transform. They spin a silken pad to secure their tail, and then spin a silken thread called a girdle to hold them steady. The Black Swallowtail caterpillars I raise harden up at this point, forming a strange, striped comma-like appearance. This stage usually lasts several hours or overnight. Suddenly, without warning, a slight thrashing motion will begin and the outer skin will be sluffed off. I’ve only managed to see this happen once or twice. Underneath the skin is a beautiful green or tan chrysalis. The color will depend on what the caterpillar has formed its chrysalis upon. I usually find the butterflies emerge within two weeks of forming the chrysalis unless they are late Autumn butterflies, in that case they will winter over and emerge in the late Spring.
Most of the caterpillars choose the window/screen area of the back porch to form a chrysalis upon. Sometimes, I lose track of their whereabouts, and then I will be surprised to suddenly find a chrysalis in a very strange place, or one outside the porch door, (there is a small opening beneath the door where they can exit if they choose) or they will completely disappear in a hidden spot and suddenly I will have an unexpected butterfly flying on the porch. I’ve included a few photos below of this year’s strange resting spots for the metamorphosis.
This one was a music lover and chose the spot to form a chrysalis beneath a window chime. When the time came, he left his melodious resting place, climbed out, dried off, and spread his wings before he flew away.
Once in a while a caterpillar will choose poorly, such as this terrible resting spot on a screen door spring. A bad choice can mean big problems, and that is a bit of a tease for Part IV.