COORDINATED WALKING OF STICK INSECTS ON A MERCURY SURFACE

SUMMARY Adult stick insects walk on a mercury surface at step frequencies in the range 1-4 Hz with a coordination similar to that found in free-walking adults at their maximum step frequency of 3 Hz. The amplitude of leg movement covers the same range as that found in free-walking animals. The use of a mercury substrate effectively removes mechanical interactions between the legs, showing that such influences cannot be the cause of the coordinated behaviour observed in this experimental situation. The dependence of the maximum step frequency upon the resistance to retraction provided by the substrate suggests that feedback from the periphery determines the step period. The variation in the anterior extreme position of a leg is less than that of the posterior extreme position, indicating that the latter may be more strongly influenced by coordinating interactions between the legs.