How does an earthworm move through soil?

Earthworms move through soil using a hydrostatic skeleton, which relies on a fluid-filled body cavity partitioned into segments to provide structural support. Their movement is characterized by peristaltic contractions of the body wall, involving two primary muscle layers: an outer layer of circular muscles and an inner layer of longitudinal muscles.12

To move forward or burrow, the earthworm follows a coordinated cycle:
* Extension: Circular muscles at the anterior end contract, causing those segments to narrow and elongate, pushing the head forward.32
* Anchoring: The worm uses setae—bristle-like structures—to grip the soil and prevent backward slipping.3
* Contraction: Longitudinal muscles then contract, shortening the segments and pulling the rest of the body forward.31

This process occurs in waves of contraction that pass backward along the body. Because the coelom is divided into segments, the fluid pressure remains localized, allowing for precise, controlled movement. This system is highly effective for burrowing, though it requires moist conditions to prevent the worm from drying out.12