Tiger beetles outsmart bats with clever ultrasonic mimicry, shows study

Many tiger beetles that are active at night produce a high-pitched, ultrasonic warning signal to ward off bats. Credit: Harlan Gough.

Bats are the main predators of night-flying insects, using echolocation to hunt in the dark.

Many insects, including moths, beetles, crickets, and grasshoppers, have evolved ears to detect these high-frequency bat sounds.

However, tiger beetles have taken this a step further by producing their own ultrasonic signals when bats are nearby.

For 30 years, scientists were puzzled about why tiger beetles made these sounds, but a new study has finally solved the mystery.

Harlan Gough, the lead author of the study published in Biology Letters, conducted his research at the Florida Museum of Natural History.

He believed that tiger beetles must gain a significant advantage from making these sounds, despite the risk of making themselves more detectable to bats.

Tiger beetles are unique among beetles in producing ultrasound in response to bats. While about 20% of moth species can do this, tiger beetles provide a fresh perspective on this behavior. Gough and his team began by confirming that tiger beetles indeed produce ultrasound when bats are around.

The researchers spent two summers in the deserts of southern Arizona, studying 20 different tiger beetle species.

They found that seven of these species responded to bat attack sounds by moving their elytra (the hard shells covering their wings) slightly backward.

This movement caused their hind wings to strike the edges of the elytra, creating a faint buzzing sound. While barely audible to humans, bats can hear these higher frequencies clearly.

Gough noted that while many insects can hear bats, only a few can respond with their own sounds. Moths, for example, often have specialized structures for making these noises. Tiger beetles, however, use a different method involving their wings and elytra.

To understand why tiger beetles produce these sounds, researchers tested several theories. They first thought the beetles might be using the sounds to jam bat echolocation, similar to some moths. However, they quickly ruled this out as the beetles’ sounds were too simple.

Next, they considered whether the beetles used the sounds to warn bats that they were toxic. Many tiger beetles produce defensive chemicals like benzaldehyde and hydrogen cyanide.

To test this, the researchers fed 94 tiger beetles to big brown bats. Surprisingly, 90 were completely eaten, and only two were rejected, indicating the beetles’ chemicals were not effective against these bats.

The final theory was that tiger beetles might be mimicking the sounds of toxic moths to trick bats. Comparing recordings of tiger beetle and tiger moth sounds, the researchers found a clear overlap.

This confirmed that tiger beetles, which aren’t toxic to bats, mimic the ultrasonic signals of toxic tiger moths to avoid being eaten.

Interestingly, this behavior is only found in night-flying tiger beetles. The 12 species that are active during the day and hunt other insects using their vision showed no response to bat sounds. This indicates they have lost the ability to react to bats since they don’t face the same threat.

The study suggests that ultrasonic mimicry might be more common among nocturnal insects than previously thought.

However, human activities like noise and light pollution could disrupt these delicate ecological interactions.

Understanding these processes is crucial, as changes to our environment can have significant impacts on wildlife.

The study highlights the importance of preserving natural habitats and minimizing human impact to protect these intricate and fascinating behaviors. Researchers believe there are many more examples of ultrasonic mimicry yet to be discovered, emphasizing the need for continued study in this field.