Vibrational alarm communication in the African fungus-growing termite genus Macrotermes (Isoptera, Termitidae)

Abstract

A sophisticated system of vibrational long distance alarm communication was found in the African fungus growing termites Macrotermes bellicosus and M. subhyalinus. When disturbed in their nests and in their extended gallery systems, soldiers produce vibrational signals by drumming their heads against the substratum. The drumming signals are trains of pulses of substrate vibrations with pulse repetition rates of 26 Hz in M. bellicosus and 13 Hz in M. subhyalinus. In both species, the carrier frequency was about 1000 Hz and the signal amplitudes about 0.5 m/s2 (acceleration, RMS). By using artificial stimuli, we examined the characteristics of the stimuli that can elicit drumming behaviour, the termites' sensitivity to substrate vibrations, their reaction time to stimuli, and their ability to discriminate vibrations of different temporal structures. We also investigated the behavioural responses of termites to drumming signals and the mechanism of long distance propagation of drumming signals through the nest and foraging sites. We found that the soldiers are extremely sensitive to vibrations, responding to vibrations with amplitudes as small as 1-2 nm by drumming themselves. This behaviour leads to the propagation of the vibrational alarm through a chain of drumming soldiers, resulting in a retreat of the termites into their nest. The termites’system of social long distance communication seems to be unique in insects.