Walking in Sticky Situations

Stick insects can usually be seen doing one of two unexciting things: standing still or walking. During walking, stepping movements are generally considered to be governed by one to several control centres associated with the joints that make up each leg. In order to walk in a coordinated fashion, the activity of these control centres must be synchronised, so that all the joints in one leg are doing the right thing at the right time to produce a ‘step.’ This is not a simple task because stick insects have to walk in many ways, including backwards and even sideways to cross uneven terrain or avoid obstacles. It would be very complicated to have a different set of rules for each walking direction, yet this is what most previous research has proposed. Setting out to find a sensory signal that stick insects could use to synchronise the activity of their leg-control centres, U. Bässler and colleagues tested the effect that vibration might have on the insect’s locomotion control. Although they don’t feel vibrations while they walk, so vibration isn’t a signal that the insects use in their daily comings and goings, the team have discovered that vibration signals applied by the experimenter are capable of reversing the direction of movement in all leg joints, no matter what the joints are doing. This is an optimistic result; having found a single coordinating stimulus that works in principle (if not in reality), there may be other stimuli that the insect uses in normal behaviour.