Most folks who live in the Eastern part of the United States can probably identify an Eastern Tiger Swallowtail butterfly (Papilio glaucus) when they see one. Eastern Tiger Swallowtails are large and have a distinctive pattern of bright yellow and black on their wings. However, not all Eastern Tiger Swallowtail butterflies are yellow—females come in two distinctly different variants, black and yellow.
The yellow morph looks a lot like a male, but with a conspicuous band of blue spots along the hindwings that the males do not have. The dark morph female has similar markings, but most of its body color is black, like the one below that I spotted last week at Green Spring Gardens. The perfect condition of its wings this late in the season suggests to me that this is a newly emerged butterfly.
So why do the females come in two colors? I read an interesting on-line article about this subject entitled “Why are you that color? The strange case of the dark phase tiger swallowtail.” The author speculates that the dark morph is an evolutionary attempt to mimic a similar-looking Pipevine Swallowtail butterfly that predators know is toxic, a practice known as Batesian mimicry. So, in theory the dark morph would have a better chance of survival. For unknown reasons, however, the males do not seem to be as attracted to the dark morph females, “These guys are apparently traditionalists and prefer the good ol’ yellow and black that their species is known for.” So the genes that might benefit species survival are not always passed on.
© Michael Q. Powell. All rights reserved.
Beautiful shot, Mike!
Pretty!
Thanks.
Interesting to know!
My eyes are delighted and my mind is informed. Thank you.
Thanks, Michael. I love that kind of reaction. 🙂
Me too!
There definitely have been advantages to joining the dark side, or the variant wouldn’t have been prosperous enough to persist. So there must be enough open-minded and–dare I say it?–endarkened males to make it work.
The dark side? Yikes, it sounds like we are in the caught up in the world of Star War. Indeed the dark variant persists, but has not become the dominant one. Apparently males like to have the freedom of choice.
I never knew this! Thanks for teaching me something today.
You’re welcome, Nina. I’m like a new teacher who is only one chapter ahead of the students. I am passing on info as I learn it. 🙂
LOL Mike, as a former teacher I really get that metaphor. You are a lifelong learner. It’s something I aspire to be.
I am curious by nature and a bit of a non-conformist. Those two traits push me to want to learn more and to challenge the conventional wisdom whenever I can.
Nice natural history post, Mike. I knew of the variation but not the potential strategy behind it. Nice shot too.
Thanks, Steve. It is often hard to judge the accuracy of what I read on the internet, but it is interesting to at least think of possible explanations of what we see.
Until this photo I never noticed that dark swirl on those upper wings. Absolutely stunning!
Thanks, Molly. As you know well, I love capturing details in my photos whenever I can.