Black Swallowtail butterflies have frequented the backyard garden every summer, laying their eggs on the dill. They usually arrive early and stay well into late summer, so there might be as many as two crops of Black Swallowtail caterpillars in the backyard (see an earlier post on this subject).
I wasn’t surprised to see what I thought was a Black Swallowtail butterfly zooming around the wildflower garden, nectaring on the coneflowers the other day, and went out to get some photos.
Black Swallowtail, Spicebush Swallowtail and Pipevine Swallowtail butterflies co-occur along with the black form of the Eastern Tiger Swallowtail throughout most of their ranges in the midwestern and eastern parts of the U.S. The four species are part of a large Batesian mimicry complex, with the Black, the black form of the Eastern Tiger, and Spicebush butterflies copying the color pattern of the unpalatable Pipevine Swallowtail to protect them from predation. At least three other species, as well as the males of several of the six species mimic the female Pipevine’s color patterns.
It is thought that the more palatable female butterflies, in particular, profit from mimicking the unpalatable species because they spend more time with their wings extended while laying eggs, and thus increase their vulnerability to predation during that time. Mimicry works well when predators have experienced the real thing — i.e., the unpalatable Pipevine Swallowtail butterfly. However, since its range does not include Minnesota (yet), the color patterns of the mimics won’t work to their advantage here.