How do leeches move with their anterior and posterior suckers?

Leeches move using a method known as bottom creeping, which employs a contract-anchor-extend cycle facilitated by their anterior and posterior suckers.1

To move, the leech first anchors itself to a surface using its posterior sucker. Once secured, it utilizes its circular muscles to contract, which elongates the body and allows it to stretch forward. The anterior sucker then attaches to the surface. After the anterior end is fixed, the posterior sucker releases, and the leech uses its longitudinal muscles to contract and shorten its body, pulling the posterior end toward the anterior attachment point. This cycle is repeated to achieve locomotion.21

This movement is supported by a hydrostatic skeleton—a fluid-filled structure that allows the body to change shape without changing volume, providing a firm yet flexible base for muscular action. While this creeping motion is common, leeches can also swim by maintaining their dorsoventral muscles in a contracted state and producing undulations through waves of longitudinal muscle contraction.12