Caterpillar sonic defences: diversity of vocalisations in silk and hawk moth (Bombycoidea) larvae

ABSTRACT

Several Bombycoidea caterpillars, renowned for their large size and diverse appearances, possess an intriguing hidden talent – the ability to ‘vocalise’. Vocalisation is a rare form of sound production in insects, whereby sounds emanate from the oral cavity by air being forced through the foregut. Here, we report on vocalisation in 10 Bombycoidea species that occur across three families. Sounds in all 10 species are evoked in response to simulated predator attacks. Species were identified as vocalisers based primarily on video evidence of mouthparts being open during sound production. Vocalisations, when considered collectively across all 10 species studied, sound like a train of ‘hisses’ (sound units) that occur following an attack. Each sound unit comprises a series of pulses (4–104 on average) and is broadband with high dominant frequency (24–49 kHz on average). Given that vocalising species occur in different families across this large superfamily, we asked whether related species shared similar sound features. We found considerable overlap between sound characteristics of different vocalising species, suggesting a shared mechanism overall. However, distinct differences were also noted between families, suggesting that vocalisation may have evolved multiple times within Bombycoidea. The evolutionary origins and specific functions of vocalisation in caterpillars are discussed.

KEYWORDS:

• Defence sound
• insect
• acoustic
• Saturniidae
• Sphingidae
• Brahmaeidae

Acknowledgements

We are grateful to all those who helped us obtain specimens for this study: V. Bura, D. Janzen, W. Hallwachs, the parataxonomists at Area de Conservación Guanacaste (ACG), A. Fleming, A. Kawahara and his lab members, A. Dookie, and Worldwide Butterflies. We are additionally grateful to V. Bura and C. Rosi-Denadai for conducting video and audio recordings of selected species.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

For access to acoustic data from this study, please contact the corresponding author at [email protected].

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/09524622.2024.2309355.

Additional information

Funding

This work was supported by Discovery Grants from the Natural Sciences and Engineering Research Council of Canada [RGPIN 2014-05947 and RGPIN-2020-07056] to JEY, and a Postgraduate Scholarship (Doctoral programme) from the Natural Sciences and Engineering Research Council of Canada [PGSD3-518236- 2018] to MLL.