Bat-Moth Arms Race

Radar warning receivers, jammers, stealth fighters... Those are all modern inventions of humans, right? Wrong.

Members of my laboratory discovered that Ecuadorian tiger moths...produce a cacophony of clicks when they are targeted by an echolocating bat. The moths intercept the sonar signals of an approaching predator using “bat detectors”—ears tuned to high frequencies—and answer them. The anti-bat sounds are produced by blisters of cuticle called tymbal organs located on either side of the thorax. Each tymbal has 30 or so ridges on it, arranged in a striated band. During activation, underlying muscles deform each ridge in succession, producing a train of clicks. The tymbal produces a second train as it returns elastically to its original shape. The anti-bat clicks are produced at a rate of up to 4,500 clicks per second, meaning that over half of the time that the bat is trying to process echoes, it is also receiving spurious moth-created clicks. This behavior is the hallmark of a sonar jammer. The tymbal organs are a characteristic of Bertholdia and its relatives, and their taxonomic distribution suggests that the organ is an ancient weapon against sonar-wielding bats.

My graduate student Aaron Corcoran determined that Bertholdia’s broadband clicks cause hunting bats to miss their targeted prey both in the laboratory and in the field... Corcoran also showed that jamming moths produce their signals only when the bat has “locked on” to them and they are in great danger. The moth determines this threat by sensing a combination of increasing bat cry intensity and a decrease in the interval between bat cries. The threshold for sound production in Bertholdia is closely matched to these parameters and allows the moth to unambiguously determine whether it has been targeted.

The latest known escalation of the bat–moth arms race is the discovery of a stealth bat by Holger Goerlitz, Marc Holderied and their colleages at the University of Bristol. The aerially hawking bat Barbastella barbastellus has lowered the intensity of its echolocation calls by 10 to 100 times. This shift allows them to remain undetected by eared moths until they are very close and the outcome is a fait accompli.

Clever monkeys though we sometimes are, we can't hold a candle to millions of years of experimentation and field tests conducted by Mother Nature. That's why I'm convinced things like faster-than-light travel and time travel are possible: we don't have to figure out how to do it, because Nature has already done so. All we have to discover is how Nature accomplished it.