Flowers with Sex Appeal

Jennifer Nemec

Imagine you’re a thynnine wasp blithely flying around the Australian countryside looking for a date. You spy what looks like a lady wasp waiting for your approach. It even has an ever-so-pleasant and feminine bouquet. When you investigate further, however, you find out that it’s an imposter ?– a flower that mimics a female wasp ?– and all you’ve got for your trouble is a dusting of pollen.

What you’ve just experienced is an encounter with an Australian wasp orchid. To carry out its own reproductive cycle (to be pollinated), it has adapted to look and smell very attractive to male wasps. Adaptation to resemble another organism is called mimicry.

Mimics exist in all kinds of places. Scientists have identified several types, most named after the naturalists who first defined them. The flower with sex appeal is a Pouyannian mimic. The fly that looks a whole lot like a dangerous wasp is a Batesian mimic, as is the tasty butterfly species that wears the colors of an unpalatable one. We had an encounter with what we discovered was a third type here at the office.

“You bug people!” Jean exclaimed. We had just looked at what had to be our 500th “Monarch” butterfly photo, and for perhaps the fourth or fifth time Hank, our editor, and I had said, “That’s a Viceroy,” at exactly the same moment. (We had to agree with her, we are bug people. I even entered my collection at the county fair as a youngster, and Hank, well, I think Hank’s interested in anything even remotely to do with soil [don’t say “dirt”] or growing things.) This led to a discussion of mimicry.

Until relatively recently, Viceroys were the textbook example of Batesian mimicry. Monarch caterpillars spend their leisure time eating milkweed leaves containing a toxic chemical that eventually makes their adult self taste bad. Viceroys look very similar to Monarchs and were thought to be protecting themselves by wearing an unpalatable disguise.

Then, a couple of enterprising fellows did a study to determine the pala-tability of the Viceroy and Monarch. They also threw in some Queen butterflies (a southern relative of the Monarch) and tasty swallowtail-types as a control group. Like me, you might be picturing the “blind taste test” ?– “four out of five blackbirds prefer the taste of Swallowtails to Monarchs.” You’re not far off.

David Ritland and Lincoln Brower fed butterfly abdomens (without their tell-tale wings) to red-winged blackbirds and watched which ones they ate. Published in Nature on April 11, 1991, their findings showed that Viceroys may be even less tasty than Monarchs.

This makes them Mullerian mimics, a relationship where several species that are unattractive to predators share a color scheme. Another example of Mullerian mimicry would be those brightly colored, and incredibly toxic, poison dart frogs in the Amazon. And have you ever noticed how many stinging insects have black and yellow stripes?

One of the mysteries of mimicry is why the “fooled” organisms don’t learn the difference. One of the theories about our poor wasp is that he has such a small chance of getting a date that he has no choice but to check out every venue. So, the smug little orchid can rest easy knowing he’ll keep coming back, even if he’s been fooled before.

Associate Editor Jenn Nemec has been interested in insects since her 4-H days, developing the ability to use the word “proboscis” in a sentence.