Bold claim: some cricket-like defense isn’t just a bluff—pupal hisses can scare off predators. A Kobe University team has now unpacked how these eerie sounds are produced, unlocking new avenues for studying how predators react to defensive noises across insect life.
Like humans who raise their voices to deter danger, certain insects vocalize to deter threats. For example, some moths emit sounds at various life stages to fend off attackers; until now, pupal sounds were thought to arise mainly from rubbing body parts against each other or against a surface. “We became intrigued after noticing that both larvae and pupae of a hawkmoth species make surprisingly loud noises when stimulated,” explains SUGIURA Shinji, an ecologist at Kobe University.
To probe the mechanism, Sugiura and colleagues exposed larvae and pupae of the buff-leaf hawkmoth (Phyllosphingia dissimilis) to forceps taps emulating a peck from a bird or bite from a predator. They tracked movements and sound production for each specimen and examined how internal organs contribute to the sounds.
Published in the Journal of Experimental Biology, the researchers report that most mature larvae and about half of the pupae reacted to contact by producing sounds and whisking their bodies in quick bursts. Underwater tests revealed the source: the sounds emanate from the animals’ respiratory openings, visible as air bubbles. Sugiura emphasizes the novelty: “Previously, pupal sound production was attributed to friction between body parts or with the substrate. This study provides the first clear evidence of a sound-production mechanism in pupae driven by forced air.”
Why would forced air be used to generate noises in the first place? Sugiura offers a clear hypothesis: both larval and pupal stages produce similar sound patterns that mimic snakes’ warning calls. Since hawkmoth larvae and pupae likely face predators such as birds and small mammals—listening prey that themselves can be prey to snakes—it’s plausible these insects acoustically imitate snake warnings to deter threats.
Future work could explore whether similar air-driven acoustic mechanisms exist in other groups and how predators respond to these defenses when confronted with such sounds.
The study was funded by the Japan Society for the Promotion of Science (grant JP17K08158) and conducted in collaboration with researchers from the Forestry and Forest Products Research Institute.
Kobe University, a national institution with roots dating back to the Kobe Higher Commercial School in 1902, today stands as a leading Japanese research university. With more than 16,000 students, over 1,700 faculty members, 11 faculties, and 15 graduate schools, the university aims to blend social and natural sciences to nurture interdisciplinary leaders who can tackle society’s challenges.
