Some centipedes don鈥檛 swim by paddling their many legs, but by wiggling their body from tail to head 鈥� the opposite direction of motion that snakes use to move across water.
at the Georgia Institute of Technology and her colleagues used high-speed cameras to observe how brown centipedes (Lithobius forficatus) move across the surface of water. Brown centipedes are found in the UK and North America, and don鈥檛 live up to their name 鈥� each centipede has just 28 legs affixed to a body comprising a head and 14 identical segments.
In 32 trials, the team placed a single brown centipede in a tank full of water. These arthropods were too light to dive under the water but could move across its surface. As each centipede floated on water, the team saw its legs wiggle a bit, but Diaz says the animals really only moved forward because they were undulating their whole body.
Advertisement
鈥淪nakes and eels do this too, but our centipedes did it the 鈥榳rong鈥� way,鈥� says Diaz. She says that the brown centipedes undulated in a motion that began at their tail, while other elongated animals typically shimmy starting from their heads.
To better understand this, the researchers made a simplified plastic model of a large segment of a brown centipede with four legs, and analysed how it interacted with water when dragged. They also developed a theoretical model of all the forces acting on the centipede鈥檚 segmented body as it swims. This revealed that the legs affected the drag forces acting on the body in such a way that it was easier for the animal to perform tail-to-head undulations instead of the reverse. In fact, says Diaz, amphibious centipedes tuck their legs in when underwater and swim more like snakes, because they don鈥檛 experience the same drag effect.
at the University of Ottawa in Canada says that the model provides a simple way to view a motion that is very complex because centipede bodies consist of many identical segments, all of which sense their environment. It is an open question whether the tail-to-head undulations result from a central command from the animal鈥檚 brain or if parts of the nervous system in each segment respond somewhat independently to forces in their environment, says Standen.
How an animal鈥檚 motion changes on the surface of water isn鈥檛 always intuitive, but understanding it can be instructive for designing animal-inspired robots that can move from land to water, says at the University of Washington in Seattle. One of Diaz鈥檚 colleagues, , also at the Georgia Institute of Technology, says that his team is already building centipede-like robots that could be used for monitoring crops and would have to navigate water in ponds or ditches.
Reference:
