It had long been known that some moth species sent out ultrasonic clicks, but it wasn’t 2009 that bat and moth interactions were investigated in the lab. Earlier studies had shown that when clicks are associated with unpalatable prey, bats could learn to avoid the clicks’ source in future. Another study had demonstrated that inexperienced bats could be startled by incoming clicks. To look for evidence supporting the sonar-jamming hypothesis, researchers at Wake Forest University (North Carolina) tied a Bertholdia trigona moth (a particularly loud-clicking moth) to a piece of string and let big brown bats try to hunt it.
The bats routinely missed the moth, even after multiple attempts on multiple nights. The “unpalatable” hypothesis could not explain this (young bats were used who hadn’t associated clicking with bad taste), neither could the “startle” hypothesis (after multiple nights, the bats would have habituated to the clicks and learnt to catch the moths). Further tests using clicking and silenced moths (moths with a small hole in their sound-producing structures, or tymbals) confirmed this result - silenced moths were caught every time, while clicking moths were still missed. It’s extremely convincing evidence that tiger moths can jam bat sonar.
“This reveals that even a small moth can defeat the most sophisticated acoustic predator known,” said researcher Aaron Corcoran, a biologist at Wake Forest University and co-author of the paper. “It’s a fantastic example of an escalating arms race between predator and prey, with each trying to constantly one-up the other.”
Timing has an important role in this sonar-jamming. B. trigona can produce around 4,500 clicks a second, and all these clicks make it extremely hard for the bat to hear its own. Later research revealed the moth’s clicks hinder the bat’s ability to detect distance, as well as disrupting bats’ echolocation attack sequence.