Centipedes (Chilopoda) and millipedes (Diplopoda) are both many-legged arthropods belonging to the group called myriapods. Although they appear similar with their elongated, segmented bodies, they represent two distinct classes of life. These groups have fundamentally different anatomies and ecological roles, which dictate how they move, what they eat, and how they defend themselves.
Leg Arrangement and Movement
The most immediate physical difference between these two myriapods is the arrangement of their legs along the body segments. Centipedes possess a flattened body shape and feature a single pair of long legs on nearly every segment. These legs project outward, allowing the centipede to move rapidly in a quick, serpentine fashion, which aids its predatory lifestyle.
Millipedes, in stark contrast, have a more rounded, cylindrical body profile. The defining feature is the presence of two pairs of shorter legs on most segments, giving them the class name Diplopoda, meaning “double foot.” These multiple legs are positioned directly beneath the body, resulting in slow, wave-like, methodical movement. This arrangement is better suited for pushing through soil and leaf litter rather than for speed.
Diet and Feeding Methods
The contrasting leg arrangements reflect a deeper difference in how each creature obtains nutrients. Centipedes are strictly carnivorous hunters, preying on insects, spiders, and other small arthropods. Larger tropical species can even subdue small vertebrates. To accomplish this predatory role, centipedes use a specialized pair of modified front legs called forcipules, located just behind the head. These claw-shaped appendages grasp prey and inject venom to quickly immobilize the meal.
Millipedes, conversely, are primarily detritivores. They feed mainly on decaying organic matter, such as moist leaf litter, rotting wood, and soft plant tissue. Millipedes use chewing mouthparts, known as mandibles, to grind up this dead vegetation, assisting in the decomposition process. Their role as recyclers of nutrients makes them beneficial contributors to soil health.
Defensive Strategies and Risk
The differences in diet also dictate their respective defense mechanisms and the risk they pose to humans. Centipedes, being active predators, use their speed to escape or deploy the same venomous forcipules used for hunting. A defensive bite from a centipede is typically painful, often compared to a bee sting, but the venom is rarely medically significant to a healthy adult.
Millipedes lack venom-injecting structures and rely on passive defense. When threatened, a millipede’s primary reaction is to curl its body tightly into a defensive coil, protecting its softer underside and head. They also possess repugnatorial glands along the sides of their bodies that release noxious, foul-smelling chemical secretions. These chemicals, which can include benzoquinones or hydrogen cyanide, act as a deterrent to predators. Contact with these secretions may cause minor skin irritation or temporary discoloration.