The viceroy butterfly is a copycat. With its orange wings divided by black lines, it looks a lot like a monarch butterfly.
Those thin black lines are important because that’s one way you can tell the two apart. The viceroy has a thin line that is parallel to the outer black line on its wing. The monarch has a u-shaped line on its wings.
The viceroy is also smaller, and it’s not poisonous. The monarch is poisonous because of what it eats as a caterpillar – milkweed.
Retired University of Montana Western biology professor Jack Kirkley pointed out the similarities and differences between the two in a recent email. Biologists like Jack call the copycat creation “Batesian mimicry.”
“This is where an edible species (the viceroy butterfly, in this case) has evolved the defensive adaptation of looking like an inedible (toxic) species … (namely the monarch butterfly),” Jack wrote.
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Any bird that eats a monarch will get sick and be unlikely to eat one again. So when it sees a similarly colored viceroy, it will probably avoid eating it.
“Hence, this learned avoidance of orange and black butterflies gives protection to both the poisonous species (the monarch), which serves as the unpleasant ‘model,’ as well as protecting the nonpoisonous species (the viceroy), a pretender which benefits from the protection of its disguise … although just being the harmless ‘mimic,’” Jack explained.
How did the viceroy come to mimic the monarch? That’s one of the amazing wonders of nature Jack will explain next week.
— Brett French, french@billingsgazette.com
