Q: I found several black and green striped caterpillars on my Italian parsley plant.
A: They are swallowtail butterfly caterpillars, sometimes called parsley worms. The butterflies laid their eggs on your plant back in July. Unless you desperately depend on the size of your parsley crop, I recommend you let the caterpillars do their thing. You can plant fresh parsley plants in a few weeks; the caterpillars will be long gone by then.