They were most likely black swallowtail caterpillars. Butterflies lay their eggs on specific host plants that the caterpillars are adapted to eat. In the case of black swallowtails, host plants are those in the carrot family, such as carrot, parsley, dill, rue and fennel. If you wish to support this beautiful butterfly, consider planting more parsley than you need for yourself, or covering some of the plants with netting. Also consider planting multiple BS host plants so the eggs don't all get laid on your parsley.
They were most likely black swallowtail caterpillars. Butterflies lay their eggs on specific host plants that the caterpillars are adapted to eat. In the case of black swallowtails, host plants are those in the carrot family, such as carrot, parsley, dill, rue and fennel. If you wish to support this beautiful butterfly, consider planting more parsley than you need for yourself, or covering some of the plants with netting. Also consider planting multiple BS host plants so the eggs don't all get laid on your parsley.