Eastern Black Swallowtail Caterpillar on my Bronze Fennel.
I poked its butt and it tried to poke me back. Look at those (I assumed to be poisonous) yellow "horns". Terpenes, which are apparently part of a foul smelling substance the osmeterium emits.
Photo One: https://www.weasyl.com/submission/683980/fennel-caterpillars
http://definingyourhome.blogspot.com/2010/05/bronze-fennel-for-butterfly-gardens.html