Insect pupae hiss like snakes for defense. A Kobe University team now reveals the mechanisms, opening the door to further studies involving predator reactions to defensive sounds.
Just as you would shout or make noise to drive off a perceived threat, some insects have been known to produce defensive sounds. Some moths, for example, have been observed producing sounds to ward off predators at multiple developmental stages; pupal sound production has so far been attributed mainly to physical friction between body parts. "We became interested in this topic when we noticed that the larvae and pupae of a hawkmoth species produced surprisingly loud sounds when stimulated," says Kobe University ecologist SUGIURA Shinji.
In order to explore how this works, Sugiura and his team examined how larvae and pupae of the buff-leaf hawkmoth (Phyllosphingia dissimilis) respond to being touched by forceps simulating an attack, like a bird peck or predator bite. The team recorded both body movement and sound production responses for each larva and pupa and also studied how the animals' internal organs were involved in the sound production.
In the Journal of Experimental Biology, the team now reports that the majority of mature larvae and half of the pupae used in testing reacted to being touched, with both producing sounds and rapidly moving their bodies. Underwater testing then revealed that these sounds were being released through the animals' respiratory openings, which were visible as air bubbles. Sugiura explains the significance of this finding: "Until now, pupal sound production was thought to occur only through physical friction between body parts or against the substrate. This is the first evidence demonstrating a sound production mechanism in pupae that is driven by forced air."
But why would these insects use forced air to make these sounds in the first place? Sugiura goes on to provide a scaly suggestion: "Both the larvae and pupae of this species produce similar acoustic patterns. Their hissing air sounds resemble the warning sounds made by snakes. Because hawkmoth larvae and pupae are likely preyed upon by birds and small mammals — animals that may themselves be attacked by snakes — we hypothesize that this hawkmoth species acoustically mimics snake warning signals to protect itself."
Further research could open the door to investigating whether similar mechanisms occur in other taxa and examine the behavior of potential predators when exposed to these defensive sounds.
This research was funded by the Japan Society for the Promotion of Science (grant JP17K08158). It was conducted in collaboration with researchers from the Forestry and Forest Products Research Institute.
Kobe University is a national university with roots dating back to the Kobe Higher Commercial School founded in 1902. It is now one of Japan's leading comprehensive research universities with over 16,000 students and over 1,700 faculty in 11 faculties and schools and 15 graduate schools. Combining the social and natural sciences to cultivate leaders with an interdisciplinary perspective, Kobe University creates knowledge and fosters innovation to address society's challenges.
