Snake slithering explained in articles in ScienceNOW 8 June 2009 and BBC News 9 June 2009.
Snakes can propel themselves forward by pushing against objects in their path such as rocks and twigs, but they can also move along smooth surfaces using a slithering movement, known scientifically as “lateral undulation” because it leaves an S-shaped track. David Hu, a mechanical engineer at the Georgia Institute of Technology in Atlanta, and colleagues, have studied the scales on snakes’ bellies to see how they could enable this movement.
Hu’s team measured the “coefficient of static friction” (how much an object grips a surface when at rest) by placing anaesthetised snakes on a sloping board with the snakes facing in different directions. The friction was highest when the snakes were placed facing upwards. This means the snakes could use differences in friction to propel themselves forward using wave-like muscle contractions which move the scales. Hu explained: “If the friction were equal in all directions, a snake would just slither in place, as if it were on a treadmill.”
During the study one snake showed its ability to slither on smooth surfaces by escaping across the floor and disappearing. Hu said, “we didn’t know where it was until we got a printer jam.” The snake survived to slither another day.
Editorial Comment: Difference in scale friction is only useful when the snake already possesses the right muscle contractions to move its body in the only way to take advantage of gripping scales – an S movement. Now ponder the fact that all the fossil evidence tells us scaled snakes once had legs and they lost them, so their sinuous body movement is a primary one for use with legs (many legged reptiles still use it), and when legs were lost, such S shaped movement was readily adapted to slithering along a surface with advantage taken of the pre-existing scales as its one remaining grip mechanism. If snakes degenerate any further and lose gripping scales they are in serious trouble!
Evidence News, 24 June 2009