Look out! A great step for locust-kind

Locusts watch where they walk using a visual guidance system similar to that of humans, scientists have learned.

In a series of experiments, researchers observed the insects climbing a ladder while a high speed camera caught every stumble and missed step.

The locusts' task was made more difficult by having one eye painted over, or having their antennae or front leg sensors removed.

The scientists also watched what happened when a rung of the ladder was removed mid-step.

They discovered that, rather than "feeling" their way, the insects relied on vision to pinpoint every foothold.

Humans and other mammals do much the same thing, though in a more complex fashion.

The locusts displayed a level visual brain processing previously thought to be too sophisticated for insects, according to the scientists.

Dr Jeremy Niven, from Cambridge University, who led the study reported in the journal Current Biology, said: "Visually guided limb control is often thought to be complicated and require sophisticated computations because you have to place your limb in a position you can only see, not touch.

"The visual control of limb placement in the locusts suggests that this can be achieved by much smaller-brained insects. It's another example of insects performing a behaviour we previously thought was restricted to relatively big-brained animals with sophisticated motor control, such as humans, monkeys or octopuses."

The study revealed some key differences between the way locusts and humans walk.

Having no binocular vision, the insects rely on visual input from a single eye to control leg movements on that side of their body.

Unlike humans and other mammals, such as cats, locusts also commit themselves to a particular foothold before lifting a leg. If something changes mid-step, they miss their target.

In contrast, a human will be watching for unexpected hazards while taking a step and can make adjustments if necessary.

It was a long fascination with insect vision that led Dr Niven to investigate locust ladder walking.

"Most studies of insect vision have concentrated on insects using vision during flight because insects such as bees and flies do spend a lot of time flying," he said.

"Other insects, such as stick insects, crickets and cockroaches, spend a lot of time walking, but they all have relatively small eyes and long antennae to 'feel' their way through the environment.

"Locusts spend time both walking and flying and have short antennae and large eyes. This started us thinking about whether it was possible for locusts to use vision to find footholds."

He added: "The study really emphasises how insects can achieve similar results to vertebrates like humans or cats with few neurons, probably by simpler mechanisms."