Black Swallowtail Caterpillar

He is on bronze fennel, one of the favoured host plants. I planted the bronze fennel last fall to attract them to my yard. I've had 7 caterpillars so far this spring.

The black swallowtail caterpillar has an orange "forked gland", called the osmeterium. When in danger, the osmeterium, which looks like a snake's tongue, everts and releases a foul smell to repel predators. -Wikipedia