Sunday, 21 August 2016

Luna moth's long tail could confuse bat sonar through its twist

Date: August 15, 2016
Source: University of Washington

The long hindwing tails sported by many moths have long been suspected as a strategy to confound predators. The moths are active mainly at night, so they don't need a visual disguise -- they need to avoid nocturnal hunters that navigate by sound.

Researchers at the University of Washington and Johns Hopkins University took a detailed look at the acoustics of the common luna moth, to see how long tails could throw off predators that use echolocation to pursue prey. Results published in the Journal of the Acoustical Society of America suggest a strategy for how even a fairly small tail could confuse bats on the hunt.

"The interesting thing about these tails is they are not just extensions -- there is a twist toward the end," said first author Wu-Jung Lee, a researcher at the UW Applied Physics Laboratory who did the research as a postdoctoral fellow at Johns Hopkins. "We think that twist could be a key for how the tails function acoustically."

The study shows that without any tail, the echo center is a bullseye right on the moth. But the twisted tail creates an echo from all directions that tends to shift the echo cloud past the tip of the moth's body. With the tail's reflection, about 53 percent of the time the echo center from experimental chirps fell past the tip of the moth's abdomen. "If the bat always aims for the highest-amplitude echoes, there's a very small percentage of the time that the tail echoes would be dominant," Lee said. "But maybe by displacing the echo center, that can do the trick."

Striking patterns on some butterfly wings are well-studied visual decoys that have evolved to confuse birds and other daytime hunters. The new paper is part of emerging research that explores acoustic camouflage in moths and other nocturnal creatures.

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