Jamming Moths Block Bat Sonar

19 July 2009
Posted by Chris Smith.

Some species of moths have evolved bat-sonar jamming abilities, scientists have discovered.  Writing in this week's Science, Wake Forest University researcher William Conner and his colleagues have shown that certain moth species can fire off rapid salvos of clicking sounds which can throw pursuing bats off course by jamming their navigation systems.

Tiger mothInsectivorous bats locate, track and catch their prey chiefly by emitting ultrasound pulses which bounce back from surrounding objects, including edible objects, and guide the bat towards its target in the same way that submariners use sonar.  But many moths have compensated by evolving organs called timbals, which are the insect equivalent of a bongo drum.

These ring-shaped structures sit on the rear of the animals' abdomens and enable them to emit clicking sounds at frequencies that the bats can hear.  Many of these moths have also evolved to taste unpleasant so that bats learn to associate hearing the sounds with a bad-tasting meal afterwards and so they leave these noisy moths alone.

But what researchers hadn't realised until now is that some moth species, including the tiger moth (Bertholdia trigona), have taken this defense strategy one wing-beat further and developed a way not just to warn bats off but also to actively block their sonar systems altogether.

The Wake Forest team tested big brown bats (Eptesicus fuscus) in a flight chamber equipped with infrared video cameras and ultrasound recorders. The bats learned to home in on and grab moths tethered in one part of the room. The team followed the fortunes of 4 test bats and compared how they performed against both moths that had been rendered incapable of making clicks and intact 'clickable' moths.

The team found that the bats successfully targeted non-clickin moths with 100% accuracy, which was four times more often than with clicking moths. So when it comes to sonar defence, moths have got it clicked it seems.

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