legcount

Legcount is a basic descriptive term used in anatomy and biology to denote the number of legs an organism uses for locomotion. In most contexts it refers to true, movable walking limbs and excludes appendages primarily used for other functions such as wings, fins, tails, or leg-like projections that do not bear weight. Legcount appears in taxonomic descriptions, ecological surveys, and comparative studies of locomotion.

Across major groups, legcount follows broad patterns. Insects typically have six legs as adults. Arachnids commonly have eight legs. Vertebrates show substantial variation, ranging from two legs in humans and many birds to four in most quadrupedal mammals. Some lineages have reduced or lost limbs, such as snakes and caecilians; others develop additional legs or leg-like structures in certain contexts, including some crustaceans that possess multiple leg-bearing appendages (for example, decapods with ten walking legs, called pereiopods).

Specialized groups provide extremes. Millipedes possess many legs with two pairs per body segment, resulting in large legcounts. Centipedes have one pair of legs per body segment, with numbers that also vary widely among species. The counting convention typically refers to walking legs; other appendages—such as antennae, jaws, or cerci—are not counted as legs.

In practical use, legcount informs taxonomy, ecological and functional studies of locomotion, and the design of legged robots, where gait and stability depend on the number of supporting limbs.