The world of Nature always boggles my mind no matter what I am studying. There is always something that totally astounds me. One example is the dark morph of the female Eastern Tiger Swallowtail (Papilio glaucus). That’s one in the photo above. Yes, a Tiger Swallowtail. Not yellow, but black. Your location will influence how frequently you’ll see this dark form. The further south the more frequent. In the blog, BackyardWildlifeConnection, Terry W. Johnson says, “In middle Georgia, my neck of the woods, more than 90 percent of all female eastern tiger swallowtails are black.” Another site suggests that 10 percent of female population is the dark morph.
Higher numbers occur in the south because of the prevalence of the host plant of Pipevine Swallowtails (Battus philenor), Aristolochia which imparts a toxin (or an extremely bitter taste) to both the caterpillar and the butterfly. The female dark morph Tiger Swallowtail is mimicking the Pipevine Swallowtail. This mimicry gives these dark females protection, since those Pipevine Swallowtails are often avoided by predators because of their extremely bitter taste.
The dark female Tiger Swallowtail sometimes shows a trace of the tiger stripes, but to see the stripes the lighting must be just right. Very subtle. Males prefer yellow females, but the black form of the female is less attractive to predators so they have a higher survival rate. So yellow Tiger Swallowtails are either male or female. Dark Tiger Swallowtails are always female. Yellow females produce yellow offspring. Dark females produce dark offspring. This is one of those things in the world of Nature that is way beyond “just” impressive.
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