Last week, I was in the front yard, talking photos for iNaturalist observations. Elaine, a neighbor stopped by with her dog, Roscoe. While we were visiting, we saw a two-tailed swallowtail (Papilio multicadata) eastern tiger swallowtail (Papilio cresphontes) flitting around. After she left, I noticed the butterfly alight on the leaf of our wafer ash (Ptelea trifoliata) and curl up her abdomen (see photo above). Ah HA! She was laying an egg!
I was right. I found that newly deposited egg and then an older egg. Then I found some caterpillars that looked like bird poop. Larva! Awesome! I took some photos and uploaded them to iNaturalist. Awhile ago, I returned with my big camera and got some more images. Aren't they all just cool?
Oh, those orange attachments are called the osmeterium. That's a forked gland that the caterpillar extends when it feels threatened. The gland shoots out a smelly fluid as a defense mechanism. Several times, the caterpillar below pointed its osmeterium in the direction of my poking finger.
UPDATE November 7, 2017: More photos...