Female Black Swallowtails fly close to the ground to look for host plants. Females lay one egg per host plant. The eggs are laid on the leaves and flowers. The egg is yellow. It later forms a red ring around the center. It will also form a red top. It will turn dark gray just before hatching. It takes about 10 days to hatch. In a lab test, females laid a total of about 200 to 430 eggs. They laid about 35 to 50 each day.