University of Florida Study shows that Spiders may have driven the Evolution of Butterflies, not Birds

A recent study from the University of Florida shows that some types of a butterfly's defense may be driven by enemies one-tenth their size.

Researchers believed that large predators, mainly birds, influenced the evolution of the butterfly.

In the first behavioral study to directly test the defense mechanism of hairstreak butterflies, UF lepidopterist Andrei Sourakov found that the appearance of a false head - a wing pattern found on hundreds of hairstreak butterflies worldwide - was 100 percent effective against attacks from a jumping spider.

"Everything we observe out there has been blamed on birds: aposematic coloration, mimicry and various defensive patterns like eyespots," said study author Andrei Sourakov, a collection coordinator at the Florida Museum of Natural History's McGuire Center for Lepidoptera and Biodiversity on the UF campus. "It's a big step in general and a big leap of faith to realize that a creature as tiny as a jumping spider, whose brain and life span are really small compared to birds, can actually be partially responsible for the great diversity of patterns that evolved out there among Lepidoptera and other insects."

Sourakov's behavioral experiments at the McGuire Center showed the Red-banded Hairstreak butterfly, Calycopis cecrops. Their spots and tail imitate a false head, which allow it to escape 16 attacks from a jumping spider, Phidippus pulcherrimus. When 11 other butterfly and moth species from seven different families were exposed to the jumping spider, they were unable to escape attack in every case.

Sourakov videotaped the experiments and analyzed the results in slow motion.

"From the video, you can see the spider is always very precise," Sourakov said. "In one video, the spider sees a moth that looks like a leaf and it walks very carefully around to the head and then jumps at the head region. The spider has an innate or acquired ability to distinguish the head region very well and it always attacks there to deliver its venom to the vital center to instantly paralyze the prey. Most importantly, the spider is very small, so sometimes its prey is 10 times larger."

The species of hairstreak butterfly and jumping spider used in the experiment are both common in the southeastern U.S., with similar relatives spread worldwideDavid Wagner, a professor of ecology and evolutionary biology at the University of Connecticut who was not involved with the study, said the research shows scientists need to rethink what drives adaptive coloration patterns because the results suggest that "birds are only part of the story."

The research published online March 8 in the Journal of Natural History shows small arthropods, rather than large vertebrate predators, may influence butterfly evolution.