Believe it or not, one of our most misidentified butterflies is the eastern tiger swallowtail. This might come as a surprise to you since it is our state butterfly and is one of the largest butterflies that visits our yards. This reason for this is this gorgeous butterfly has two color phases.
The wings of the males are predominantly yellow and marked with vertical stripes. This is the color form most people recognize. Females, on the other hand come in either yellow or black phases. If you look closely at the wings of a dark female, you will usually seen telltale black stripes. The black form of the eastern swallowtail is the phase many people do not realize is also an eastern tiger swallowtail.
In middle Georgia, my neck of the woods, more than 90 percent of all female eastern tiger swallowtails are black. However, dark females are far less common in some other parts of the country. Some lepidopterists – folks that study butterflies – suggest that the percentage of dark females is greatest where pipevine swallowtails are most abundant. For example, black females are far less common in New England and others parts of the butterfly’s range.
Interestingly, dark females are prone to produce dark daughters while yellow females usually have yellow mothers.
Dark females have a better chance of surviving long enough to lay eggs than yellow females. The reason why is that dark females look much like the poisonous pipevine swallowtail. The pipevine has an extremely bitter taste. If bird or other predator tries to eat one, it rarely goes back for seconds or even attacks a butterfly that looks like it.
I would be interested in know the percentage of black females to yellow females you see in your yard. If you conduct a survey of the eastern tiger swallowtails in your yards, let me know what you find.