Humans have greatly helped the Black Swallowtail. They brought non-native carrot species from Europe to North America. The Black Swallowtail uses these plants as host plants. Before humans cut down forests, Black Swallowtail were rare. They were only found in small prairies, wetlands, and openings in forests. However, in the northeast, people are not farming as much as they used to. This is making the Black Swallowtail become less common in this part of its range.