Earthworms have four pairs of setae on each segment except the first and last. These setae are stiff, tiny bristles and help the worm move forward in conjunction with its muscles. Each pair of setae is used as a worm explores its environment.
The earthworm grips the soil with the setae on the back part of its body. It elongates its body by squeezing its circular muscles, pushing the front segments forward. The setae on the front segments of the earthworm grip the soil as the earthworm contracts its longitudinal muscles to pull the back segments forward. The worm repeats this cycle until it reaches its destination.