Centipedes are predatory arthropods belonging to the class Chilopoda, an ancient group characterized by their long, segmented bodies. The name “centipede” literally translates from Latin as “100 feet,” which is a common source of misunderstanding. Centipedes are related to millipedes, but their anatomy and lifestyle are vastly different. The actual number of legs a centipede possesses is highly variable and depends entirely on the particular species.
The Truth About Centipede Leg Counts
No known species of centipede has exactly 100 legs, despite the common name suggesting otherwise. The actual number of legs ranges from a minimum of 30 (15 pairs) up to over 300 legs (191 pairs). This wide variation is determined by the species and the number of leg-bearing segments that make up its trunk.
The most important biological rule concerning centipede legs is that the number of leg pairs is always an odd number. This means that a centipede will never have an even total number of leg pairs, such as 100 or 200 legs.
The number of leg-bearing segments can vary significantly even within a single order, such as the Geophilomorpha, which can have between 27 and 191 pairs of legs. This variation occurs because different species have different developmental patterns for generating their body segments. The odd number of leg pairs is a consistent feature across the entire class Chilopoda.
Centipede Anatomy and Segment Structure
The body of a centipede is composed of a head followed by a long trunk made up of numerous segments. With few exceptions, nearly every segment of the trunk bears exactly one pair of legs. This single pair of legs per segment is a defining characteristic of centipedes.
The odd number of leg pairs results from a specific developmental pattern. In the majority of centipedes, the first segment behind the head is modified, and the last two segments are small and legless, contributing to the final odd count. Some species, like the house centipede, hatch with few pairs of legs and gain more segments with each successive molt (anamorphosis). Other centipedes, such as those in the orders Geophilomorpha and Scolopendromorpha, are epimorphic, meaning they hatch with their full complement of legs already present.
Distinguishing Centipedes from Millipedes
Centipedes and millipedes are both multi-legged arthropods belonging to the subphylum Myriapoda, but they have distinct anatomical differences that reflect their ecological roles. The most reliable way to tell them apart is by observing the number of legs per body segment. Centipedes have only one pair of legs per segment, and their bodies are typically dorsoventrally flattened.
Millipedes, in contrast, have a more cylindrical shape. They possess two pairs of legs on most segments. This occurs because the millipede’s segments are fused together in pairs during development, a structure known as a diplosegment. The legs of a millipede are positioned directly underneath the body, enabling them to push and burrow through soil and leaf litter.
The difference in leg structure corresponds to their feeding habits. Centipedes are active, agile predators that use their single, laterally placed pair of legs to move quickly and chase prey. Millipedes are primarily detritivores, feeding on decaying organic matter, and their numerous legs are adapted for slow, powerful movement. When threatened, a millipede often curls into a defensive spiral, while a centipede relies on its speed and venom for defense.
Specialized Appendages and Their Function
Centipedes possess two pairs of specialized appendages that are not used for locomotion. The forcipules are modified legs located on the first body segment, just behind the head. These pincer-like structures are the centipede’s primary weapon.
The forcipules contain venom glands and are used to inject paralyzing venom into prey, which includes insects, spiders, and small vertebrates. The specialized appendages allow the centipede to subdue its meal quickly before consuming it.
The final pair of legs at the posterior end of the body are also modified and are referred to as the ultimate legs. These appendages are often longer or thicker than the walking legs. Their function is not related to movement; instead, they can be used for sensory input, grasping and holding prey while the forcipules deliver venom, or for defense and intimidation. These specialized appendages highlight the centipede’s adaptation as an efficient hunter.