Wingtip folds and ripples on saturniid moths create decoy echoes against bat biosonar

Thomas R. Neil, Ella Kennedy, Brogan J. Harris, Marc W. Holderied

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Sensory coevolution has equipped certain moth species with passive acoustic defenses to counter predation by echolocating bats.1,2 Some large silkmoths (Saturniidae) possess curved and twisted biosonar decoys at the tip of elongated hindwing tails.3,4 These are thought to create strong echoes that deflect biosonar-guided bat attacks away from the moth’s body to less essential parts of their anatomy. We found that closely related silkmoths lacking such hindwing decoys instead often possess intriguing ripples and folds on the conspicuously lobed tips of their forewings. The striking analogy of twisted shapes displayed far from the body suggests these forewing structures might function as alternative acoustic decoys. Here we reveal that acoustic reflectivity and hence detectability of such wingtips is higher than that of the body at ultrasonic frequencies used by hunting bats. Wingtip reflectivity is higher the more elaborate the structure and the further from the body. Importantly, wingtip reflectivity is often considerably higher than in a well-studied functional hindwing decoy. Such increased reflectivity would misdirect the bat’s sonar-guided attack toward the wingtip, resulting in similar fitness benefits to hindwing acoustic decoys. Structurally, folded wingtips present echo-generating surfaces to many directions, and folds and ripples can act as retroreflectors that together create conspicuous targets. Phylogenetically, folds and ripples at wingtips have evolved multiple times independently within silkmoths and always as alternatives to hindwing decoys. We conclude that they function as acoustic wingtip decoys against bat biosonar.
Original languageEnglish
Pages (from-to)4824-4830
Number of pages6
JournalCurrent Biology
Volume31
Issue number21
DOIs
Publication statusPublished - 8 Oct 2021

Funding

We thank Margaret Gamble for her assistance in caring for moth pupae and sourcing dry Lepidoptera species throughout the project. We thank Meg Barstow and George Barnes for their efforts in collecting pilot data for the study and the development of analyses. We also thank the technicians of the Alicona Microscope facility at the University of Bristol for their expertise and training in 3D surface scanning. B.J.H. is grateful to the New Phytologist Trust for the award of a PhD studentship. This study was supported by the Engineering and Physical Sciences Research Council (grant EP/T002654/1 ).

FundersFunder number
Engineering and Physical Sciences Research CouncilEP/T002654/1

    Keywords

    • acoustic decoy
    • sensory deception
    • ultrasound
    • bat
    • moth
    • echolocation

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