This Morning Outside

by Diane Porter

August 28, 2009
In the grass at Birdwatching Dot Com
Fairfield, Iowa

A viceroy butterfly stayed a long time in my path this morning, warming itself in the slanting light of the rising sun.

Viceroy Butterfly
Copyright 2009 Michael and Diane Porter

The straight dark line across the hind wings is the shadow of the stem in the lower right. The thinner, curving dark line close to the margin of the same wings is an easy field mark that shows this is a viceroy and not the look-alike monarch butterfly.

Young Blue Jay The monarch butterfly is toxic. A young bird, such as a fledgling blue jay, who doesn't know any better yet may eat a monarch. It will get a major tummy ache, but it won't die. It will live to remember the experience, and it will never eat a monarch again. That's not much direct help to the monarch that got eaten, but it helps the species as a whole. Birds learn to avoid monarchs and anything that looks like them.

By resembling the butterfly that teaches a lesson to birds, the viceroy shares the benefit.

Not all butterflies of the same species look exactly alike, any more than all people look alike. There are slight individual differences. And we know that species can change their appearance over time. (For example, in England, the peppered moth has changed from light to dark and back to light again over the last two hundred years.)

At one time the two monarch and the viceroy butterflies may have had only a slight, accidental resemblance. But among the viceroys, there was an advantage to looking like a monarch, being avoided by hungry birds, and living to reproduce. Since offspring tend to look like their parents, the viceroys gradually came more and more to mimic the toxic monarch.

Now they look so much alike that it's easy to mistake one for the other. An easy mistake for birds and for people as well.