Someone posted the question online: does a house centipede have more legs than a centipede? The answer is weirder than you'd expect — because "centipede" turns out to be a whole family of animals with wildly different leg counts, from 15 pairs all the way up to 191.

The House Centipede: 15 Pairs, Grown Over Time

Meet the house centipede first. An adult has 15 leg-bearing segments, each carrying one pair of legs — the pair on the very end breaks off easily (the one in this photo already lost it). Its back plates are unusual: only eight plates, which do not match the segments underneath. So even with every leg gone, you could still recognize it.

House centipedes also grow new segments as they age — but only until adulthood. A freshly hatched one has just four pairs of legs, an accidental spider costume. Juveniles are rarely seen.

The Centipede: 21 or 23 Pairs, Fixed at Birth

Most centipedes have 21 pairs of legs; some have 23. That number is fixed from birth. The juvenile in this photo is a rough-eared centipede (Otostigmus scaber); the other common type, the sharp-jawed centipede, carries 23 pairs.

Those "Legs" Near the Head

Both house centipedes and centipedes have one extra pair of special legs at the front — venomous, claw-like, used for hunting. Strictly speaking they are not counted as real legs, and this is how the animals inject venom: not through fangs, but through these legs.

The Question Doesn't End There

The family gets stranger.

Stone centipedes also have 15 leg-bearing segments and 15 pairs of legs, but their back plates alternate large and small — except where two large ones sit together, which looks bizarre up close. After house centipedes, they are the most primitive group.

Cup centipedes are living fossils: only two species survive, found in Tasmania and New Zealand. They hatch with 12 pairs of legs and grow to 15 after a single molt — halfway between primitive and modern patterns.

Soil centipedes are the newest branch, and they somehow unlocked the segment limit. They can carry anywhere from 27 to 191 pairs of legs — always an odd number, for reasons nobody knows. The count is fixed at birth and never changes after molting. Burrowing in soil has deformed them oddly: long, thin, flattened, with very short legs — and a head shaped like an extended shovel.

A Glorious Family

Apart from the rather unfortunate cup centipedes, every major group is doing well today, with real diversity and a niche of its own. House centipedes and centipedes even found a way to coexist with us — the naked apes. Not bad for a family whose members disagree about everything from leg counts to body plans.

Want to see what the same arthropod body plan looks like under a microscope — segments, legs, and all? WWAI includes a Culex mosquito specimen where body segments and wing veins are clearly visible. Just search "WWAI" in your app store and download it today.

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References:

[1] Centipede anatomy and leg counts. Britannica. https://www.britannica.com/animal/centipede

[2] Scutigeromorpha (house centipede). Encyclopedia of Life. https://eol.org/pages/6377

[3] Centipede. Wikipedia. https://en.wikipedia.org/wiki/Centipede

[4] Geophilomorpha: the soil centipedes. Wikipedia. https://en.wikipedia.org/wiki/Geophilomorpha

All illustrations are AI-generated.

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