What’s the buzz? Ultrasonic and sonic warning signals in caterpillars of the great peacock moth (Saturnia pyri)

Abstract

Caterpillars have many natural enemies and, therefore, have evolved a diversity of antipredator strategies. Most research focuses on those strategies (crypsis, countershading, and warning coloration) targeting visually guided predators. In contrast, defensive sounds, although documented for more than a century, have been poorly studied. We report on a novel form of sound production—chirping—in caterpillars of the common European Great Peacock moth (Saturnia pyri). Chirps are broadband, with dominant peaks ranging between the sonic (3.7 kHz) and ultrasonic (55.1 kHz) and are generated by a rapid succession of mandibular “tooth strikes.” Chirp trains are induced by simulated predator attacks and precede or accompany the secretion of a defensive chemical from integumental bristles, supporting our hypothesis that these sounds function in acoustic aposematism. We propose that these caterpillars generate multimodal warning signals (visual, chemical, and acoustic) to target the dominant sensory modalities of different predators, including birds, bats, and invertebrates.

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Acknowledgements

We thank B. Wenczel and R. Schafroth for supplying S. pyri, T. Eberhard for technical assistance, and two anonymous reviewers for helpful suggestions to the manuscript. We gratefully acknowledge research funding by the Natural Sciences and Engineering Research Council of Canada (JEY), the Canadian Foundation for Innovation, and Ontario Innovation Trust (JEY).

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Correspondence to Jayne E. Yack.

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A S. pyri larva is attacked near the head capsule region with blunt forceps (simulating an attack by an avian predator). The caterpillar responds primarily by stridulating an]d releasing chemicals from the scoli (not observable in the video). (MOV 994 kb)

A S. pyri larva is attacked near the posterior body region with blunt forceps (simulating an attack by an avian predator). The caterpillar responds by stridulating, releasing chemicals (not observable in the video) and thrashing its body toward the site of the attack. (MOV 1.13 mb)

Close-up movements of the mandibles during two chirp trains. During the first chirp train, each of the three chirps is associated with the right mandible sliding against the inner surface of the left mandible. During the second chirp train, the animal switches sides so that the left mandible slides against the inner surface of the right. (MOV 3.66 mb)

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Bura, V.L., Fleming, A.J. & Yack, J.E. What’s the buzz? Ultrasonic and sonic warning signals in caterpillars of the great peacock moth (Saturnia pyri). Naturwissenschaften 96, 713–718 (2009). https://doi.org/10.1007/s00114-009-0527-8

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Keywords

  • Caterpillar
  • Acoustic
  • Aposematism
  • Chemical defense
  • Ultrasound