Hydrostatic skeletons, such as that of Oligochaeta and Hirudinea, allow the locomotion of animals with soft segmented bodies. In this paper crawling of Oligochaeta, and in particular that of earthworm (Lumbricus terrestris), is analyzed from a biomechanical point of view, starting from the experimental kinematic description of deformations coupled with a simple friction model. The analysis is able to predict crawling velocity with an error of about 15% with respect to the experimental measured values. Also muscular stress during locomotion is evaluated and found to be compatible with biological values.