Are Monarch Butterflies Monomorphic?

Let’s begin by taking the word monomorphic apart. Mono means one; morphic comes from Greek and means form. So essentially, the word monomorphic in biology means one form. Dimorphic, di- meaning two, refers to two forms.

The easiest way to understand these two concepts is through birds. If you look out your window and see a Blue Jay, you can’t determine the sex of the bird; male and female jays look alike. Robins, too. But you can instantly tell a male cardinal from a female cardinal. The male is red; the female brown. So jays and robins are monomorphic; cardinals are dimorphic.

Photo of male and female cardinals
Male and female cardinals. © Bonnie Taylor Barry

That’s the simple explanation. I’ll save the more complicated discussion about the intricacies of identifying the sex of birds at a banding table for another blog.

Honestly, I never thought about monarchs as being either monomorphic or dimorphic. That’s why I love research adventures. You just never know how one piece of information will lead to another. Such was the case over the weekend.

I was working on a email blast and built this banner.

Three photos, left to right, monarch caterpillar, chrysalis, butterfly

Readers will recognize the first two photos from my other monarch blog posts. The third photo came from a search for a monarch butterfly picture. It was during that search I learned that monarchs, in fact, are dimorphic. A trained eye can tell a female monarch from a male monarch. And let me write this: The difference between female and male is darned subtle! One has to find two spots.

People who tag butterflies for research are probably quite adept at sexing the monarchs. For the rest of us, unless one gets up close and personal with a monarch, and knows exactly where to look, I am thinking we will just enjoy the awe of seeing them fly, male or female.

Before closing, a chrysalis update!

This is how the chrysalis on the my house appeared on Sunday, August 16, 2020. Look at the right side of the chrysalis; you can see the wing forming.

Seven day old chrysalis
Chrysalis which formed on August 12, 2020
This photo from August 16, 2020

And, I still have a visitor or two dining on milkweed. Maybe Harry Houdini learned a trick or two from monarch caterpillars. They chew on the milkweed one moment, disappear, and then return!

Monarch caterpillar on milkweed
Monarch caterpillar on Asclepias tuberosa, August 17, 2020

The earliest we might see the monarch butterfly forming in the chrysalis above is this Wednesday, August 20, 2020.

Stay tuned.

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