A tale of four swallowtails

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).

black-swallowtail-on-dutchmans-breeches

A Black Swallowtail butterfly lapped up nectar from early spring blooming Dutchman’s breeches.  Note double row of yellow spots on the top (dorsal) side of the wing and double row of orange spots on the under (ventral) side of the wing.

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.

spicebush swallowtail

But the markings are not quite right for a Black Swallowtail butterfly.  The large whitish-orange splotches on the outer margins of the wing are only very small dashes of color.  

spicebush swallowtail

A large blue area showing on the hind wing and two rows of yellow dashes means this is not a Black Swallowtail, but the black form of the Eastern Tiger Swallowtail instead.

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.

PipevineSwallowtail-female-Bob Moul

The model — the unpalatable Pipevine Swallowtail.  Photo by Bob Moul.

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.

10 thoughts on “A tale of four swallowtails

  1. Interesting! I knew Monarchs had mimics but didn’t realize there were mimics for the Swallowtails – at least none that I had seen. Or so I thought. I went back through my Swallowtail photos and sure enough, one set looks suspiciously like a Spicebush now that I know what to look for. http://wp.me/p2oND-2kR Ooops.

    • Interesting! Well, I have to say, I was completely ignorant about the extent of this mimicry complex which involves females of the eastern tiger swallowtail butterfly as well. So that was a good learning experience.

  2. Do you get Eastern Tiger Swallowtails there as well? I get confused, because there is a black variant of the female that looks a lot like the black swallowtails that you have featured here. Life was a whole lot simpler when I knew less about these butterflies and I could simply categorize them all as black Swallowtail butterflies. Your shots are beautiful, with gorgeous backgrounds. I finally have seen a few swallowtails and caught a glimpse of what may have been a Monarch.

    • Yes, this is the eastern Tiger Swallowtail, but no, we don’t get that Black variant form (female only, I believe) that you see. At least I haven’t seen one here yet, but now I know you really have to look carefully before you reach a decision about which species of BF you are really seeing.

  3. Beautiful butterflies! We get two different Swallowtails here but I was just musing I had not seen any this year. Their preferred flower is buddleia and it is about finished now. Amelia

    • Butterfly populations seem to be spotty here. Some bloggers near me (geographically) say they haven’t seen any, while others say they are plentiful. I wigs I understood why…but that’s for a different post.

    • Butterflies seem to vary a lot in their presence from year to year, and I know you had a mild winter, so it is surprising that the butterflies are not around. Always a puzzle.

  4. Pingback: Brand new and beautiful | Back Yard Biology

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