Millipedes are invertebrates found in diverse environments globally. Often encountered in gardens or under logs, these creatures are known for their elongated bodies and numerous legs. They play an important role in ecosystems as decomposers, breaking down decaying organic matter.
The Real Number of Legs
Despite their common name, meaning “thousand feet,” millipedes do not actually possess a thousand legs. This misnomer stems from their many appendages. Most species have a leg count ranging from fewer than 100 to around 400. The Giant African millipede, for example, typically has between 300 and 400 legs.
The actual number of legs varies significantly by species and individual. Illacme plenipes, a species found in California, held the record with up to 750 legs. However, a new species discovered in Australia in 2020, named Eumillipes persephone, surpassed this record, with some individuals possessing over 1,300 legs, making it the leggiest animal known.
The Segmented Body Plan
The number of legs on a millipede relates to its segmented body structure. Millipedes belong to the class Diplopoda, meaning “double foot,” which describes their leg arrangement. Most body segments form from the fusion of two embryonic segments, resulting in each “double segment” having two pairs of legs, totaling four legs per segment.
When a millipede hatches, it typically has only a few pairs of legs and legless segments. As they grow, millipedes undergo molting, shedding their rigid exoskeleton. With each molt, they add new body segments and new pairs of legs. This continuous addition of segments and legs throughout their development allows them to reach their high leg counts.
Distinguishing Millipedes from Centipedes
Millipedes are often confused with centipedes due to their similar elongated, multi-legged appearance, but they have distinct differences. A primary distinction lies in their leg arrangement: millipedes have two pairs of legs per body segment, while centipedes have only one pair of legs per segment.
Millipede legs are typically shorter and positioned directly beneath their bodies, aiding in their slow, undulating movement, often described as a wave-like motion. In contrast, centipedes have longer legs that extend outward from their sides, enabling them to move quickly and dart around.
Their body shapes also differ; millipedes generally have a rounded or cylindrical body, while centipedes possess a flatter, more elongated body. Millipedes tend to coil their bodies into a tight spiral and may release a foul-smelling or irritating fluid to deter predators. Centipedes, being predators, are known to bite using venomous fangs, though their bites are usually not harmful to humans. They rely on their speed to escape threats.