Eastern Black Swallowtail Caterpillar

Description:

These early instar caterpillars are bird-dropping mimics. They are mostly black, spiky, and have a white saddle around their middle. The white saddle is caused by uric acid deposits that may function as an antioxidant, protecting the larvae from phototoxic chemicals in their host plants. There are usually two broods in the summer, but occasionally a partial third brood will emerge later in the season, which seems to be the case with these caterpillars. It was only 41 degrees Fahrenheit (5 degrees Celsius) when I spotted these caterpillars today, and they were very sluggish. We are expecting a frost tonight, so I fear they likely will not survive.

Habitat:

I spotted two of these caterpillars on fennel (Foeniculum vulgare) in a rural garden.

Notes:

Larvae feed primarily on plants of the carrot family and some in the rue family. They are often found on dill, parsley, fennel, carrot, and rue in gardens. In the wild, they may be found on queen-anne's-lace, poison hemlock, and lovage. The common name(s) for the caterpillars vary so much since they can be found on so many different and important cultivated plants. To give it a common name, it seems that you just pick the host plant and then add the word "worm" afterwards.