In summer, we are bombarded with the sounds of crickets and cicadas serenading the opposite sex. These vibrations travel through the air and reach our ears. Insect communication with low frequency vibration is less intrusive and much softer, but no less important. Often overlooked are caterpillars that we think of as silently munching away on a leaf. Upon closer observation, the caterpillars may not be so silent and instead may be noisily trash talking their rivals and approaching predators.
The masked birch caterpillar, Drepana arcuata, makes sounds by drumming on leaves with its mandibles and scraping the leaf with its abdomen. The sounds are audible to the human ear from about 1 meter away and are clearly audible if the caterpillar is placed near a human ear. The caterpillars communicate with 2 types of sounds. One sound is a scraping they make with the end of their abdomen. Another is drumming on the leaf with their mandibles. The caterpillars make a “nest” for themselves in a leaf using silk. The sounds are made upon detection of an approaching caterpillar. The sounds are a warning that the leaf is occupied and the occupant might fight or bite the intruder. These sounds can prevent conflict between caterpillars that could kill one or both of them.
The sounds have a deterrent effect on generalist predators that do not use these caterpillars as prey. The caterpillar may be signaling toxicity or bad taste a subject for futher investigation.We can conclude that the caterpillars can distinguish among vibrations caused by a predator and vibrations caused by a caterpillar of the same species from differences in the response. The caterpillars will respond to another caterpillar at a greater distance. The predator must approach more closely before the caterpillar responds. The response to the predator is more vigorous. The mandible tapping and abdomen scraping is more rapid.
These signals can be detected by the approaching predator and by the approaching caterpillar. Both will leave the leaf in response to the sound. The sense organs responsible for detection of the vibrations are not fully characterized. In some cases the location of the organs responsible for vibration detection are unknown. With the development of more sophisticated sound recording equipment we can learn much more about caterpillar chatter and eavesdrop on their conversations.
Dr. Yack and colleagues discuss their work in the recent paper: “Vibration detection and discrimination in the masked birch caterpillar (Drepana arcuata).” JOURNAL OF COMPARATIVE PHYSIOLOGY A: NEUROETHOLOGY, SENSORY, NEURAL, AND BEHAVIORAL PHYSIOLOGY
R. N. C. Guedes, S. M. Matheson, B. Frei, M. L. Smith and J. E. Yack
You can hear Dr Jayne Yack discussing her caterpillar work on the Radio Show, Quirks and Quarks: