War is a constant arms race. You need to be better than your enemy, which includes having better strategies if you want to survive another day. The same goes for predators and their prey. Bats are great insect hunters with their specialized echolocation, but some insects have developed a way to “trick” the signal.
As reported in Science Advances, researchers have discovered that several types of silk moths have evolved longer tails that are capable of deflecting the echoes away from their body, which is ultimately the only thing the bat is interested in. Bats don’t eat moth wings.
"Once we knew that the tails of silk moths deflect echoes away from their body, we were interested in whether there were optimal anti-predator shapes," co-author Akito Kawahara, associate curator at the Florida Museum of Natural History, said in a statement. "One of the first things we did was go into the collections and look at specimens. There was a ton of variation in hindwing length, shape, color and twisting. We wanted to analyze these characteristics in an evolutionary framework to see what was happening."
The team looked at wing shapes across many different types of moths and were able to construct a detailed family tree of wing shapes. They discovered that certain families of moth changed shape abruptly. This suggests that certain shapes are indeed better to avoid getting eaten by a bat. The team identified four shapes: two types of extra-long tails, short tails, and long lobes. These were even seen in moths that were not closely related.
"We see moths moving toward peaks of optimal shapes with unrelated moths evolving in similar ways," Kawahara added. "This speaks to bats' selective pressure on their prey."
The team tested moths with different shaped wings against bats to assess a baseline of success and then modified the tails on certain moths to see if that changed the outcome. The bigger and longer the tails, the more likely the moths were to escape. African moon moths, known for their very long tails, were the most skilled. They avoided bats 73 percent of the time.
"Bats are incredibly acrobatic and very skilled hunters, but moths are also powerful flyers and have an incredible turn radius," explained lead author Juliette Rubin, who completed the research as a Boise State master's student. "They seem to be pretty well-matched adversaries."
Moths and bats have been caught in this battle for tens of millions of years, but according to the researchers, it appears that bats have yet to figure out how to outsmart the silk moth's deflective technique.