The luna moth carries around a sonar scrambler

For an insect, the world is full of predators, and without big teeth or claws, hiding is often the best survival strategy. Camouflage is great: many bugs blend in perfectly with their backgrounds and some even manage to look exactly like plants. But what do you do against a predator that isn't hunting with its eyes?

Luna moths are preyed upon by some of nature's most efficient aerial hunters: bats. Camouflage is no good here, because the bats hunt in the dark and use echolocation to zero in on their target. But it seems the moths aren't entirely helpless. The secret to their success? Their strange, twisting tails.

The strange, twisting tail of the luna moth acts like a sonar shield. Image: Christy, Flickr

A study from last year found that big brown bats have an easier time catching luna moths who have lost their tails. This got scientists thinking: what if, instead of confusing their predators' vision, the moths' tails were somehow messing with the bats' sonar?

To test the hunch, the researchers designed an experiment that involved tethering flying moths in place and using special equipment to send ultrasonic chirps at the bugs as they fluttered about, and then reading the echoes. The goal was to get a "bat's-eye-view" of the moths.

Of course, this wasn't a perfect representation of what the bats "see". As lead researcher Wu-Jung Lee of the University of Washington explains, "[w]e don't know what type of signal processing the bats are using" – but the experiment did provide a rough idea. And sure enough, the researchers found that the moths' tails interfered with the echoes.

In contrast with the stronger, ever-changing echoes coming off of the moths' large flapping wings, the twisted shape of the tails created a persistent weak echo signal. According to the researchers, this could make the insects trickier to catch, and harder to track as they fly.

And luna moths are not the only ones who rely on "acoustic camouflage" to stay safe. With the ever-present threat of death-by-bath, ghost swift moths seem to have a habit of flying low through tall grass, where the plants might interfere with bats' sonar. Other moths give off sounds of their own to confuse their squeaking predators. Some tiger moths have even been known to mimic the sounds produced by nasty-tasting moths, much like certain delicious and harmless snakes mimic the colouration of venomous species.

For every crafty hunting tactic, it seems, there's a defensive camouflage trick. Many predators, for example, seek food using their sense of smell, and in return, prey animals have evolved fascinating strategies to hide their scents. Even the electrosensory capabilities of sharks can be fooled: animals like cuttlefish, for instance, are known to throw their arms up over their siphons to reduce the electric signals their bodies give off.

Meanwhile, this study has left Lee wondering about the tails of other moths. Besides the luna moth, long tails are found in many species, such as the moon moths of Africa and Asia, and the "longtails" of South and Central America. It may be that rear-end "sonar shields" are more common than we've realised. Now it's up to the scientists to grab their butterfly nets and go find out.