Mimicry is Exhibit A in most evolution textbooks. Why does that species of butterfly look like this species? Or why does that bug look just like a thorn? Or why does that hover fly look a lot like a bee? Well, it's because a mimetic species, usually but not always innocuous, benefits from resembling a foul-tasting or dangerous species - the closer the resemblance, the greater the benefit to the mimic.

Thanks to the work of Lincoln Brower in the early 1960's, most of us have heard about monarch and viceroy butterflies. Fewer of us have heard of Fritz Muller's travels in the Amazon and his resulting speculation on butterflies there. And most of us, being Northeasterners, have never had the pleasure of seeing a harmless king snake that looks a lot like a poisonous coral snake.

There is little doubt that mimicry appears to be extremely common. But it is rarely as simple as the text suggests. Let's look at the complexities with the two butterflies mentioned above. As of this writing (Aug. 7), I have yet to see either a monarch or a viceroy at our homestead this summer. They were fairly common here in mid- to late summer last year. The monarch is a much-loved insect that is highly migratory and is famous for eating milkweed plants as a larva.  

Since plants can't get up and run away, many defend themselves with chemicals. In the case of the milkweed, the chemical is a cardiac glycoside that can cause the vertebrate heart to beat irregularly. As they eat, the monarch larvae store this compound, thereby passing it on to themselves as adults. The famous photo of a blue jay throwing up after eating an adult monarch is the result.     

Why did the jay eat the monarch? Because it was young and dumb and had never eaten one before. When presented with another one, it passes. "No thanks, I learned from the last one." But that raises the first question. What exactly is the benefit to a bright orange, highly conspicuous butterfly that has to be eaten by a naïve predator to "inform" the predator of its distastefulness? Further, if the viceroy is really a mimic of the monarch, and its larvae eat tasty willows and are palatable, why don't viceroys - if at all common - result in a lot more monarchs being eaten by predators who have only tasted the more common viceroys?

There is at least one more (butter)fly in the ointment. Monarch kids always eat milkweeds because their moms always lay eggs on milkweeds. But only some milkweed species are toxic. Doesn't that mean that some monarch adults, bright as can be with "warning" coloration, taste okay? And does that mean some monarchs are functionally viceroys? And what about those pesky real viceroys? Maybe we're right in the middle of an intense, evolutionary video game.

So let's ask a final question? Why are almost all bumblebee species yellow and black? All can sting, so there is no harmless look-alike tagging along on another's coat tails. For that matter, why are all skunks black and white, or all lady-bird beetles red or orange with black spots? If all these species are toxic, noxious, or otherwise gross, who benefits from whom? This is called Mullerian mimicry--and the world just got even more complex.   

Bob Engel will be back next month with "some even more outrageous tales of mimicry."