Prolegs

Prolegs are fleshy, stub-like abdominal leg structures found on the larvae of many insects, most notably caterpillars of the Lepidoptera. They are not true legs; true legs arise from the thorax and are jointed. Prolegs are typically unsegmented and terminate in clusters of tiny hooks called crochets that grip leaves, bark, or other surfaces.

In most Lepidopteran caterpillars, there are five pairs of prolegs on abdominal segments 3–6 and 10, though the exact number and position can vary by species. The presence, absence, or modification of prolegs influences locomotion. Caterpillars with a full set of prolegs move in a looping fashion, lifting the front part of the body and then bringing the rear forward to propel themselves. In many geometrid moths, the mid-abdominal prolegs are reduced or absent, producing the characteristic inching or looping gait.

Functionally, prolegs provide additional grip and stability for feeding on plant material and help with climbing toward new foliage or shelter. They appear during the larval stage and are absent in the adult moths and butterflies after metamorphosis.

Ecologically, prolegs affect feeding behavior and habitat use. Many species with prominent prolegs are agricultural pests, while others are important as prey for predators and contribute to ecosystem dynamics. The pattern and morphology of prolegs also aid in identifying larval groups in taxonomy.