It's an unconventional form of communication, but when their mound home is under attack, termite soldiers pound their reinforced heads against the ground to sound the alarm. Felix Hager, from the Ruhr University Bochum, Germany, explains that termites detect the alarming signal with vibration-sensitive organs in their legs, called chorodontal organs. But it wasn't clear whether the insect's nervous system was sensitive enough to detect the infinitesimal delay between the vibration arriving at each leg to give them a sense of which direction the sound was coming from. ‘In the nests of Macrotermes natalensis, vibrational alarm signals are propagated at 130 m s−1,’ says Hager and colleague Wolfgang Kirchner, meaning that the insects would have to be able to detect vibrations arriving at each of the legs within 0.2 ms of each other. Was this possible (p. 2526)?

First the duo tested how soldiers and worker termites responded to simulated alarm vibrations, and confirmed that worker termites flee while soldiers turn to attack. Then they tested how much of a delay the termites could resolve between vibrations arriving at their legs. First they set up two PVC platforms separated by a 1 mm gap and connected each to a loud speaker to produce the alarm signal vibrations. Next they placed five termite soldiers with their legs straddling the gap and set the platforms vibrating after delaying the vibration of the second platform by less than a millisecond.

Altering the delay from 0.29 to 0.09 ms, the duo was impressed to see that the soldiers turned toward the platform that vibrated first, just like soldiers in a real attack, and the insects could detect time differences between the vibrations arriving at their legs of only 0.2 ms. So termite nervous systems are sensitive enough to respond to the super-short time differences between vibrations arriving at their legs, which will allow them to decide how to react in the event of an attack.

F. A.
W. H.
Directional vibration sensing in the termite Macrotermes natalensis
J. Exp. Biol.