Along with the Tiger Swallowtail, this is one of the two common swallowtails in the Chicago suburbs.  The caterpillars feed on plants of the carrot family, and the female butterflies are particularly attracted to parsley and dill plants in gardens.  Like the Tiger Swallowtail, these butterflies have two generations of adults in the summer.  The first generation, as early as late April through June, emerges having overwintered in the chrysalis, and the second generation flies in late summer.