How Worms Crawl: New Mathematical Model May Create Inching Robots

Most people have seen worms and other insect larvae crawl across the ground. But exactly what movements do they use when it comes to inching through the Earth? That's a question that scientists have now answered with the help of a mathematical model which challenges the tradition view of how these creatures get around.

The most widely accepted view is that of the central pattern generator (CPG). This states that the central brain of these creatures generates rhythmic contraction and extension waves along the body. This explanation, however, doesn't account for the fact that some of these invertebrates can move even when their ventral nerve has been cut.

"When we analyze humans running there is clearly local control over movements as by the time nerve signals travel from the foot to the brain and back again, you will have taken three steps-and would otherwise probably have fallen over," said Paolo Paoletti, one of the researchers, in a news release. "We see much the same in these soft bodied animals. Rather than generating a constant wave of contraction and expansion, their movement is controlled and influenced by the contours of the surface they are moving across."

The researchers created a mathematical and computational theory in order to describe the movements they were seeing. Then, they tested this theory under different circumstances and conditions using imagined worms of different masses. In the end, they created a theory that could potentially be used to create robots that employ the same movements.

"Replicating the movement of animals in robots is very difficult and often involves the use of many sensors," said Paoletti. "This new model avoids using sophisticated sensors and control strategies, and could be used to improve robots used for entering confined spaces or which have to deal with difficult terrain."

The findings are published in the journal Proceedings of the Royal Society B: Biological Sciences.