Fooled you! Whirling tails of luna moths deflect bat attacks

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Those pretty green tails fluttering and whirling at the end of a luna moth’s hind wings turn out to be pretty good defensive weapons in an acoustic war with predatory bats.

As tips of a moth’s tails whirl in two circles behind the wings, they reflect the echolocation pings that a bat uses to find and nab prey out of the air. That can trick bats into attacking a more expendable body part, or missing the moth altogether. Jesse Barber of Boise State University in Idaho and colleagues report the finding online the week of February 16 in Proceedings of the National Academy of Sciences.

In lab experiments, big brown bats struck at the tails of luna moths (Actias luna) instead of other body parts 55 percent of the time. And when researchers trimmed those tails off the moths, tailless moths were almost nine times as likely as intact moths to be caught by a bat. For the moths, the tails seem to be about as effective as the better known moth defense against hungry bats: ears to detect the echolocation pings of an incoming predator and get out of the way.

The tail doesn’t seem to add noticeable oomph to flight, Barber and his colleagues conclude. Yet the swirly motion does seem to enhance its allure as a misleading target to bats. Of the four times that long tails have evolved in the whole family of saturniid moths, little cupped spatulas at the tip of the tails that enhance twirling have evolved too.

TAIL SPIN  As a luna moth flies in the lab, shown at one-third normal speed, the tail tips make circles in the air. In another lab video, shown at one-sixth normal speed, bats attacking moths strike at the fluttering tails — which works out well for the moths.

Credit: J.R. Barber et al/PNAS 2015