Night warfare: moths jam bats' sonar

Posted by Emma Woollacott

Winston-Salem, NC - There's nothing new under the sun. Biologists have discovered that one type of moth jams the sonar of bats with bursts of its own ultrasound.

The tactics of the Bertholdia trigona tiger moth amount to electronic countermeasures like those used in human warfare.

Other species of tiger moth are known to make ultrasound clicks, but previous studies have shown that these serve either to warn of an unpalatable taste or to startle the bats. But the jamming technique is a new discovery.

Researchers at Wake Forest University studied the moths using ultrasonic recording devices and high-speed infrared video. They concluded that the moths weren't warning the bats of unpalatability, as if this were the case the bats would eat a few before learning to avoid them. Nor were they startling the bats, as this effect would be expected to wear off as the bats became used to the sound.

Instead, they say that when the moths emitted their signals, the bats appeared to be unable to find them. Audio recordings showed that the moth clicks disrupted the bats’ cycle of echolocation calls, which normally increase as the bat nears its target. This, the researchers reckon, means that the bats were still trying to catch the moths but were confused by the clicks.

The authors write, "We show that the palatable tiger moth Bertholdia trigona defends against attacking big brown bats (Eptesicus fuscus) using ultrasonic clicks that jam bat sonar. Sonar jamming extends the defensive repertoire available to prey in the long-standing evolutionary arms race between bats and insects."

The findings are reported in Science.