A Tricky Adaptation

by Alicia Vasto, AmeriCorps member

September 30, 2015

A few weeks ago, I had the great fortune of photographing a butterfly at very close distance. I was at the new Forks of the Little River Passive Park near Star when I spotted the butterfly resting on a rock. I snuck up to it and, without breathing, slowly hovered closer and closer over it with my phone, snapping pictures every few millimeters I went. It must be one the best pictures I’ve ever taken, and I was very proud despite delaying the progress of the group I was with.

At the time, I didn’t really think anything of the butterfly I was actually taking a picture of. It was a common butterfly; I have seen many of them fluttering through the woods this summer. I assumed it was a spicebush swallowtail (as I assume every black and blue butterfly is to be honest). However, when I showed the picture to my boss last week, she knew immediately that it was not what I carelessly assumed it was. My butterfly was clearly lacking the telltale “tails” on the ends of the wings that mark a true swallowtail. So she sent the photo on to Steve Hall, invertebrate zoologist recently with the NC Natural Heritage Program, for identification. He informed us that the butterfly is actually a Red-spotted Purple (Limenitis arthemis).

Doing a quick online search of the Red-spotted Purple, I discovered I was somewhat justified in assuming that it was a swallowtail. The Red-spotted Purple is in fact a Batesian mimic of the poisonous pipevine swallowtail (Battus philenor).

Batesian mimicry is an adaptation that is common among butterfly species, and is the most common form of mimicry in the natural world. The term describes a harmless species that has evolved to mimic the warning signals of noxious or dangerous species in order to avoid predators. Predators learn to avoid unpalatable prey by associating their physical characteristics with an unpleasant experience. By taking on the coloring and patterns of the poisonous swallowtail, the Red-spotted Purple gains the benefits of the warning signal without having to go to the trouble of evolving to become poisonous itself.

Batesian mimicry is not limited to visual mimicry. Other animals have evolved ways to dupe predators using the other senses. For example, some tiger moths have adapted to mimic the ultrasonic warnings sent by foul-tasting moths to evade bats. Burrowing owls of North and South America have developed the ability to mimic rattling and hissing sounds similar to rattlesnakes when they are threatened in their burrows.

Mimicry has a price, however. The “model” of the mimicry is put at an unfortunate disadvantage when their mimics become too common. Although the mimic does not consciously disguise itself as the model, the hand of natural selection has pushed it to proliferate its mimicry. If the mimics appear in high numbers, predators may catch on to the deception and begin to ignore the warning signal, compromising the model species’ efforts to protect itself. This in turn ends up being disadvantageous for the mimic; if the mimics outnumber the models, the predator either take its chances or will learn there is an advantage to distinguishing the mimic from the model. In this “evolutionary arms race”, this often results in mimics being rarer than models.

Although Batesian mimicry is common in the natural world, it is interesting to note that the mimics are actually what are more rare in comparison to the models. Due to a remarkable selection process that has taken place over a great deal of time, mimics hide themselves in plain sight, and we can easily overlook them as we walk amongst common plants and animals in the woods. Next time you are in the woods amongst the butterflies, take a second look at them—you may be seeing more than what you initially thought.