“Crypsis,” as you should all know by now, is just a fancy scientific word for “camouflage.” Often cryptic animals will hide from predators by mimicking their background, but here’s a case in which one part of an animal mimics the other. Have a look first and see if you can figure out what’s going on.
(The photo, tweeted by Bug Girl, and posted on flickr by itchydogimages, John Horstman, is identified as a Long-Banded Silverline, Spindasis lohita, Lycaenidae. It was taken on February 23, 2013 in Simao, Yunnan, CN, using a Sony DSC-R1.)
This is a case of a “false head” in a butterfly. While the real head is inconspicuous, the posterior part of the wings bear a gaudy, attention-attracting false head, colored orange and replete with fake eyespots, fake antennae, and fake legs. Note as well that the wing patterns call attention to the fake head by converging on it.
One evolutionary explanation immediately comes to mind. Predators—and by this I mean birds—are operating on the old Chinese proverb, “To kill a dragon, first cut off its head.” Birds have either learned (or perhaps have an evolved propensity) to strike at insects by pecking at their anterior (front) section, which is far more likely to debilitate it than a peck at the rear, on the wings. By evolving a “false head”, an insect has a higher chance of surviving a bird strike since the bird pecks at the false head, allowing the butterfly to escape with minimal damage. In fact, I remember reading about studies in which on finds “false head” butterflies with the fake head are bitten far more often on the wings than str “regular” butterflies. Doug Taron at the Peggy Notebeart Nature Museum here in Chicago verifies this (and shows more false-headed butterflies):
In 1980, scientists from the Smithsonian attempted to demonstrate that predators could be fooled into attacking the wrong end of the butterfly. They collected hundreds of butterflies in Panama and Columbia, and divided them into groups based on the number of head-like features were present in their wing patterns. Consistent with the false head hypothesis, the greater the number of head-like features, the more likely wing damage due to predator attacks was to be directed to that part of the wings.
I also remember—though I can’t provide chapter and verse—that birds also automatically strike in front of what they perceive as the head, like a sniper leading a target with his rifle. This anticipates that the butterfly will take off when attacked, and that a strike directed right in front of the head will intercept it in mid-flight. This makes it even more likely that false-headed butterflies will escape predation, since the bird will be aiming behind the entire insect.
Finally, I recall that some of these butterflies actually land and then turn around 180º after landing, just in case a bird is watching them land. That will confuse the bird even more about which end is the head. I’ve found one paper in the 1982 volume of Journal of the Lepidopterist’s Society by Torben B. Larsen that substantiates this behavior in a Nigerian butterfly.
There are several species of butterfly with such patterns, which obviously are examples of convergent evolution. Here are two more:
From Urban Wildlife Guide, the gray hairstreak butterfly, Strymon melinus:
This butterfly is striking enough that its non-scientific name is the “Common false head” (photo from TrekNature by MIKE WNR [drmw]); this is the butterfly documented to do a 180-degree turn after landing: