Moth tails divert bat attack: evolution of acoustic deflection

Abstract

Adaptations to divert the attacks of visually guided predators have evolved repeatedly in animals. Using high-speed infrared videography, we show that luna moths (Actias luna) generate an acoustic diversion with spinning hindwing tails to deflect echolocating bat attacks away from their body and toward these nonessential appendages. We pit luna moths against big brown bats (Eptesicus fuscus) and demonstrate a survival advantage of ∼ 47% for moths with tails versus those that had their tails removed. The benefit of hindwing tails is equivalent to the advantage conferred to moths by bat-detecting ears. Moth tails lured bat attacks to these wing regions during 55% of interactions between bats and intact luna moths. We analyzed flight kinematics of moths with and without hindwing tails and suggest that tails have a minimal role in flight performance. Using a robust phylogeny, we find that long spatulate tails have independently evolved four times in saturniid moths, further supporting the selective advantage of this anti-bat strategy. Diversionary tactics are perhaps more common than appreciated in predator-prey interactions. Our finding suggests that focusing on the sensory ecologies of key predators will reveal such countermeasures in prey.

Keywords: Lepidoptera; Saturniidae; antipredator defense; bat–moth interactions.

Fig. 1.

Luna moth tails lure echolocating bat attacks. (A) Percentage of moths captured during interactions with big brown bats (E. fuscus). Error bars are binomial 95% CIs. Brackets show P values for comparisons using mixed-effects logistic regression. (B) Movie frames of a bat biting and removing the tail of a luna moth (A. luna).

Fig. 2.

ML molecular phylogeny of saturniid moths showing multiple independent origins of hindwing tails. Filled black circles indicate origin of tails. Open circles indicate losses. Branch colors indicate length of hindwing tail from absent (blue) to >50 mm (red), based on Phytools continuous character evolution analyses. Numbers by branches are bootstrap values. Gray shading denotes groups that have spatulate tails and contain species with tail lengths greater than 37.5 mm (the average for A. luna, n = 10). The images of saturniid moths used in these experiments are labeled: (A) A. luna and (B) A. polypheumus. Bold type and asterisks denote species that have tails longer than 37.5 mm. In combination with our bat–moth interaction data, this phylogeny suggests that tails serving a clear anti-bat function have evolved 4 times. Three additional origins of very short tails, of uncertain function, are also apparent.