Those Confusing Black and Blue Butterflies!

Well it is Spring again, that most wonderful time of year when life renews itself, and we have to figure out the names of all those confusing Spring flowers and butterflies that we have not generally seen for many months. I just encountered my first spicebush swallowtail butterfly and since it was a male, it was relatively easy to recognize (see photo). However there are a surprising number of large black and blue butterflies, many in different families and thus not closely related, that resemble one another to an amazing degree. Just for example consider the photos of four species that I have included here: the spicebush and pipevine swallowtails, the female Diana fritillary, and the red-spotted purple (a brushfoot). Considering that the males and females of some species are much more different in appearance than these butterflies from totally different families, what is going on here?

This is believed to be the result of convergence in coloration among butterflies that are poisonous to eat (especially the pipevine swallowtail that feeds on toxic Dutchman’s pipe as a caterpillar and thus serves as a model) and tasty or partially tasty mimics that find it advantageous to gain protection from a resemblance to the pipevine swallowtail. Yet why would males and females within one species be so different? For example male eastern tiger swallowtails are yellow and black as are many females, yet some females are dark, especially in the South. Male and female Diana fritillaries are always different and the male is more cryptic.

This similarity in coloration among dissimilar species should remind you of the mimicry group among orange and black butterflies (all poisonous to some degree) that feed on milkweed (monarch, queen, soldier), willow (viceroy) and passionvine (gulf fritillary).

So the predators, mainly birds, are clearly scrutinizing their prey in great detail trying to figure out which ones are good to eat and which are poisonous. The prey are doing their best to confuse the birds. The military “arms race” and strategic deterrence were obviously not invented by the Russians and Americans. Once again we are amazed by the diversity and complexity of life!

Bill Dunson, Englewood, FL & Galax, VA
wdunson@comcast.net

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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