Termite Vibration Sensing: The Chordotonal Organs and Their Appendages.

Eusocial insects like termites and ants use diverse communication methods, including pheromones, sound, and vibrations. Termites, blind and with fewer glands, rely heavily on vibrations for foraging, communication, and predator avoidance. Their appendages detect subtle signals amid noise, though the underlying physiological mechanisms remain largely unknown and understudied. We explore the role of termite legs and antennae as sensory probes. These appendages receive the vibration signals, which are detected by the leg's subgenual organ and the Johnston's organ in the antenna, and which in turn convert these mechanical environmental signals into nerve impulses sent to the nervous system. We compare these appendages in termites and ants, two eusocial, subterranean insect groups that share ecological traits but differ in trophic roles, with ants being major predators of termites. Termite legs and antennae have lower slenderness ratios (legs: 19-35 vs. 48; antennae: 23-32 vs. 61). Wasps and bees fall in between. Assuming similar material properties, termite legs likely have lower stiffness and higher natural frequencies, enhancing vibration sensitivity. The subgenual organ's position near the head may further improve detection. These morphological traits suggest termites could be better adapted for sensing a broader range of vibrations than ants. However, more specimens and species of Isoptera and Formica need to be tested to validate this claim fully. Comparing the legs of termites with ants, we found that termite tibiae amplify lower-frequency vibrations (~0-2.25 kHz), while ants show an amplification at higher frequencies (1.9-3.1 kHz). This suggests the vibrational sensitivity of termites is better adapted to wood-borne signals, which corresponds to their food, whereas ants, as generalist foragers, are tuned for diverse terrains, including light structures, such as twigs, leaves, and other plant matter. Considered together, our findings suggest that termite legs may function as an integrated auditory complex.