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. Last Updated: 07/27/2016

Ears Link Moths to Butterflies

Jayne Yack's revelation came in the dim light of an old pump house on an island in Panama in the form of seven pairs of softly fluttering wings.

Coincidence, she says, happens all the time in science. You just have to know what you're looking for.

As it turns out, Yack had been looking for something else when she first discovered a pair of ears on the wings of a small nocturnal butterfly. Her discovery twice led her to Panama, where she studied the creatures in the wild and tested the purpose of those delicate ears.

As the butterflies began to fly in their characteristic slow, graceful manner, Yack used a hand held device to emit a single burst of 25 kilohertz of sound, or 25,000 vibrations per second. The butterflies reacted immediately to the frequencies by undertaking loops, dives or a movement Yack compares to the motion of a washing machine.

"This behavior," she says, "we know is classic bat-avoidance behavior."

Ultrasonic hearing isn't unusual in the nocturnal insect world. But Yack's discovery is the first to unambiguously identify such ears in butterflies and link them to their bat-evasion efforts.

Her study offers a new glimpse into the evolutionary race between bats and their prey and a new take on the relationship between moths and butterflies.

Moths and, as it now seems, butterflies, have independently developed ultrasonic ears on different parts of their bodies at least six times throughout evolution, an unusual coincidence that suggests to Yack and other entomologists that a strong selection pressure, namely bats, shaped the insects' survival mechanisms. Some of the structures are on the thorax, some on the abdomen. The new discovery maps to the wings, a first in the insect order Lepidoptera, which includes moths and butterflies.

"The general feeling is that butterflies as we know them were once more moth-like and at some point they moved into the day," Yack says. "What we don't know is what caused them to move into the day."

Again, she suspects the answer is bats, although she admits this is little more than speculation at the moment.