It is a common misconception that centipedes have exactly one hundred legs, a belief often stemming from their name, which literally means “hundred feet.” These arthropods, known for their elongated bodies and numerous legs, raise questions about their exact leg count. However, the true number of legs on a centipede is not a fixed quantity. This variability is a distinguishing characteristic of these creatures, influenced by their species and developmental stage.
Unpacking the Leg Count
Centipedes exhibit a range in leg count, typically having an odd number of leg pairs, which translates to an even total number of legs. The total leg count can vary significantly, from as few as 30 legs in some smaller species to over 300 legs in larger, more segmented varieties.
For instance, the common house centipede, Scutigera coleoptrata, typically has 15 pairs of legs, resulting in 30 legs in total. Other species, like the giant desert centipede (Scolopendra heros), generally have around 21 or 23 pairs, totaling 42 or 46 legs. The precise number of segments, and thus legs, can even differ slightly among individuals of the same species. This variation also depends on the centipede’s age, with some species adding more segments and leg pairs as they mature.
The Segmented Body Plan
The variation in a centipede’s leg count directly correlates with its fundamental body structure: a segmented body plan. Each functional body segment of a centipede’s trunk typically bears a single pair of legs, with one leg extending from each side.
A centipede’s body is generally divided into a distinct head region and a long, multi-segmented trunk. While most trunk segments carry legs for locomotion, the very first segment behind the head features a specialized pair of modified legs called forcipules. These are not used for walking but are instead venomous claws used to capture and subdue prey. Additionally, the final segment often has a pair of modified legs that can be thicker, longer, or possess sensory functions, distinct from the primary walking legs.
Centipedes Versus Millipedes
Confusion often arises between centipedes and millipedes, particularly regarding their leg counts. The most straightforward distinction lies in the number of leg pairs per apparent body segment. Centipedes are characterized by having one pair of legs per segment. This arrangement allows for their typically faster and more agile movements.
In contrast, millipedes possess two pairs of legs per apparent body segment. This unique characteristic is due to the evolutionary fusion of two embryonic segments into what appears as a single, larger segment in the adult millipede. This double leg arrangement per segment gives millipedes a more rounded, often cylindrical body shape and contributes to their generally slower, more deliberate movement compared to centipedes.