How Many Legs Does a Centipede Have? Never Exactly 100

Why no centipede has exactly 100 legs

The name centipede comes from the Latin centum, “hundred”, and pes, “foot”. It was never meant as an exact count. Every centipede carries one pair of legs on each leg-bearing body segment, and the number of these segments is always odd, from 15 up to 191.

A centipede with 100 legs would need 50 pairs, an even number, and no species has that. A soil centipede can have 49 or 51 pairs, since both are odd, but never exactly 50.

Studies of centipede embryos suggest the reason lies in how the body forms. After a first set of segments appears near the head, new segments are added at the tail end in pairs, so the total stays odd. This developmental rule is so consistent across the class that an even number of leg pairs is not found in any species.

How many legs do different centipedes have?

Scientists divide living centipedes into five orders, and leg number is one of the clearest differences between them.

In three orders the count is fixed at 15 pairs. The big tropical centipedes of the genus Scolopendra usually have 21 or 23 pairs. The widest variation is found in the long, thin, eyeless soil centipedes, which burrow through earth like worms.

In soil centipedes the number often varies even within one species. Females usually have more legs than males, and populations in different regions can differ. The western yellow centipede, common in gardens in Britain and central Europe, has 77 to 83 pairs. The Mediterranean Himantarium gabrielis is much more variable: males have 87 to 171 pairs and females 95 to 179.

The centipede with the most legs

The record holder is Gonibregmatus plurimipes, a soil centipede from Fiji with 191 pairs of legs, or 382 legs in total. No other centipede is known to have more.

Even this champion falls far short of the millipede record. A thin, eyeless millipede from Western Australia, Eumillipes persephone, has up to 1,306 legs, because millipedes carry two pairs on most segments. The full story is in How many legs does a millipede have?.

Venom claws: the legs that became fangs

Every centipede has an extra pair of limbs that is not counted among its walking legs. The forcipules, also called venom claws or maxillipeds, sit just behind the head and curve forward under the mouth. They are the first pair of body legs, changed over evolutionary time into sharp pincers.

A venom gland runs inside each claw to an opening near its tip. The centipede uses them to grab prey and inject venom, then passes the food to its mouthparts. These claws are found only in centipedes, and they are the reason centipedes can bite while millipedes cannot.

At the other end of the body, the last pair of legs, called the ultimate legs, is also special. These legs are not used for walking. In the house centipede they are long and thin and trail behind like a second pair of antennae; in giant Scolopendra species they are thick and spiny and can be raised in a threat display.

Do centipedes grow more legs as they get older?

It depends on the group. House centipedes and stone centipedes hatch with only a few pairs of legs and add more each time they molt, a pattern called anamorphic development. The house centipede hatches with four pairs and grows to five, seven, nine, 11, 13 and finally 15 pairs. The brown centipede, Lithobius forficatus, hatches with seven pairs and also ends with 15.

Soil centipedes and the large tropical centipedes hatch with their full set of legs already formed and keep the same number for life. In these groups the mother usually curls around her eggs and young to guard them until they can fend for themselves.

Many centipedes can also shed a leg that has been seized by a predator, a defense known as autotomy. House centipedes are often seen with a few legs missing for this reason.

How do centipedes run on so many legs?

Centipedes are built for speed. Their legs stick out from the sides of a flattened body, and in many species each pair is slightly longer than the pair in front. This lets the rear legs step outside the front ones instead of colliding with them.

The house centipede takes this furthest. Its last legs are about twice as long as its first, and it can run at about 0.4 m (1.3 ft) per second, roughly 10 to 15 times its body length every second. Waves of leg movement pass along the body, with the left and right legs of each pair stepping alternately.

Centipede legs vs millipede legs

The easiest way to tell the two groups apart is to look at the legs. A centipede has one pair per segment, long legs that splay out to the sides and a body built for chasing prey. A millipede has two pairs on most of its body rings, short legs tucked underneath and a body built for pushing through soil and leaf litter.

That is why centipedes are fast hunters and millipedes are slow recyclers of dead plants, even though both are myriapods. See centipede vs millipede for a full side-by-side comparison.