Tiger beetles might employ ultrasound as a defense against bats

Tiger beetles may have evolved to mimic the ultrasonic clicks of toxic moths to fend off predatory bats, a new study suggests.

Short Summary:

  • New research indicates tiger beetles produce high-pitched clicks similar to those of toxic moths.
  • This sound-based mimicry could serve as a deterrent against bats.
  • Further studies are needed to confirm the mimicry hypothesis and understand its evolutionary implications.

When tiger beetles hear approaching bats, known for their echolocation abilities, they react by producing high-pitched clicks. This discovery was made by researchers and published on May 15 in Biology Letters. These acoustic signals mirror the sounds made by toxic moths, signaling their unpleasant taste to predators like bats. Scientists believe this form of mimicry may be more common among nocturnal insects than previously thought.

The nocturnal battle between bats and insects is intense, as many insects have developed sensitive hearing to evade bats’ echolocation. Some moths, for example, have wings and fuzz that absorb sound, making them less detectable to bats’ sonar. Others generate ultrasonic trills with their genitals, which can startle bats or disrupt their sonar. The idea that tiger beetles exhibit a similar adaptation is a fascinating addition to this ongoing evolutionary arms race.

Harlan Gough, a conservation entomologist with the U.S. Fish and Wildlife Service, along with his colleagues, sought to understand why tiger beetles respond to bat-like ultrasound with their own high-pitched clicks. Previous studies had shown this reaction, but the purpose remained unclear. The team collected 19 species of tiger beetles from southern Arizona and conducted experiments to uncover the mystery.

In their laboratory setup, the researchers tethered these beetles to a metal rod and simulated nearing bat clicks. Astonishingly, seven nocturnal species immediately pulled their forewings into the path of their beating hindwings, producing high-pitched clicks. “It’s a fascinating discovery,” said Gough, emphasizing the potential survival benefits these beetles might gain from mimicking toxic moths.

Initially, Gough and his team theorized that these clicks could signify the beetles’ unpalatability or toxicity. However, when tested, bats readily consumed 90 out of the 94 beetles offered, clearly indicating that they are not chemically defended against bats. This led researchers to discard the chemical defense hypothesis and consider mimicry as a more plausible explanation.

Acoustic analysis revealed close similarities between the clicks of tiger beetles and those of local tiger moths, which are known to be foul-tasting. “The tiger beetles are likely mimicking the ‘stay away’ clicks of tiger moths,” Gough explained. The researchers propose that this mimicry might extend across various nocturnal insects, suggesting a broader ecological phenomenon.

Ted Stankowich, an evolutionary ecologist at California State University Long Beach, commented on the significance of these findings. “Most animal warning communication research focuses on visual signals. This study highlights the importance of sound in predators’ and prey’s communication strategies,” he said. Such insights could reshape our understanding of sensory adaptations in nocturnal ecosystems.

Further research is needed to confirm these hypotheses and explore how widespread ultrasonic clicking is among the estimated 3,000 species of tiger beetles worldwide. Understanding the evolutionary timeline of these acoustic defenses relative to the emergence of echolocating bats could provide deeper insights into this fascinating survival mechanism.

“We are just scratching the surface of what’s happening in the nocturnal acoustic world,” Gough stated. He emphasized the potential for discovering similar phenomena in other insect orders, which may use sound-based mimicry to evade predators.

This study underscores the complex interplay between predators and prey in the natural world. By delving deeper into the acoustic strategies of insects like tiger beetles, researchers hope to unravel the intricate evolutionary processes shaping these survival tactics.

“There’s so much more to learn about the night sky’s acoustic environment,” Gough concluded, inviting further exploration into this captivating area of entomological research.

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