Adult woodlice have fourteen legs, arranged in seven pairs — one pair on each segment of the pereon (the main body section). This is true of every woodlouse species in the UK, from the tiny common pygmy woodlouse to the familiar rough woodlouse in your garden. Interestingly, baby woodlice are born with only twelve legs and gain their final pair after their first moult.
That's the short answer. Below we'll cover why fourteen legs works so well for woodlice, how the legs develop, what they're actually used for, and how leg count helps you tell woodlice apart from other minibeasts.
Why Do Woodlice Have 14 Legs?
Woodlice are terrestrial crustaceans — members of the order Isopoda, more closely related to crabs and shrimp than to any insect. The name "isopod" literally means "equal foot": unlike crabs, which have specialised claws and walking legs of different shapes, a woodlouse's seven pairs of legs are all roughly the same size and build.
This uniform arrangement suits how woodlice live. Fourteen legs spread evenly along a low, flattened body give exceptional stability on rough, uneven ground — bark, stones, crumbling leaf litter — and let woodlice press themselves flat into crevices where predators can't follow. They aren't fast, but they're remarkably sure-footed.
The legs do more than walk. Woodlice use them to grip and manipulate food while feeding on decaying plant matter, and to sense the texture and moisture of their surroundings. For a moisture-dependent animal with gill-like breathing structures, being able to detect a damp refuge through contact really matters.
Do Baby Woodlice Have 14 Legs Too?
No — and this is one of the most useful facts for identifying young woodlice. Newly hatched woodlice, called mancae, leave their mother's brood pouch with only six pairs of legs (twelve legs) and six leg-bearing segments. Within around a day of release they go through their first moult and gain the seventh segment and final pair of legs.
The brood pouch itself is worth a mention. Female woodlice carry their fertilised eggs in a fluid-filled pouch (the marsupium) on the underside of the body — a feature woodlice share with their wider crustacean group, the peracarids. The young develop in this protected, portable pond for several weeks before emerging as miniature, pale versions of the adults.
Like all arthropods, woodlice must moult to grow — and they do it in a way few other animals do: in two halves. The rear half of the exoskeleton is shed first, followed by the front half a few days later. A woodlouse that looks half grey and half white isn't ill; it's mid-moult. Because the exoskeleton is reinforced with calcium carbonate, woodlice need a steady calcium supply to moult successfully — which is why keepers add cuttlebone to captive setups.
How Do Woodlouse Legs Compare With Other Crustaceans?
Crabs, lobsters and shrimp — the aquatic relatives of woodlice — typically have biramous limbs, meaning each limb branches in two. Woodlouse walking legs are uniramous: a single, simple branch. This pared-down structure is lighter and better suited to walking on land than swimming or burrowing in water.
Woodlice also lack the single large carapace that covers a crab's body. Instead, their armour is a series of overlapping segmented plates, which trades some protection for flexibility — essential for squeezing under bark and stones, and for the pill species that roll into a ball.
It's also an easy way to separate woodlice from the animals they're often confused with. Insects have six legs, spiders have eight, centipedes and millipedes have far more. If it has fourteen legs and overlapping plates, it's a woodlouse. For a full breakdown of body structure, breathing and senses, see our essential guide to woodlouse anatomy.
Which Woodlice Will You Find in the UK?
Britain has around 40 native woodlouse species, but five are so widespread they're known as the "famous five":
- Common rough woodlouse (Porcellio scaber) — grey with a matt, slightly bumpy texture, up to about 17 mm. The classic garden woodlouse, and the wild ancestor of many colour morphs in the Porcellio hobby.
- Common shiny woodlouse (Oniscus asellus) — smooth and glossy with pale patches, up to about 16 mm. Part of the Oniscus genus.
- Common pill woodlouse (Armadillidium vulgare) — the one that rolls into a perfect ball, up to about 18 mm. The genus name means "little armadillo", and Armadillidium species are among the most popular kept isopods.
- Common striped woodlouse (Philoscia muscorum) — yellowish-brown with a dark stripe down the back, fast-moving, up to about 11 mm.
- Common pygmy woodlouse (Trichoniscus pusillus) — purplish-red and no more than 5 mm long, yet probably the most abundant woodlouse in Britain.
Every one of them, despite the differences in size, colour and shape, has the same fourteen legs as an adult.
Why Those 14 Legs Matter to Your Garden
Woodlice are decomposers. They feed mainly on decaying plant matter — fallen leaf litter, rotting wood, fungi and mould — and their legs are the tools that let them clamber through debris, hold food and shred it into fragments. Those fragments, returned to the soil as droppings, break down far faster than whole leaves would, recycling nutrients that plants then reuse.
This is exactly why isopods are used as cleanup crews in bioactive terrariums: the same fourteen-legged decomposition service, working inside an enclosure instead of a woodland floor.
Found Woodlice Indoors?
Woodlice indoors are almost always a symptom of damp rather than a problem in themselves. They can't survive long in a dry house, don't bite, don't spread disease, and won't damage sound, dry timber. If they keep appearing, the kindest and most effective fix is to address the moisture: repair leaks, clear gutters, improve ventilation and seal gaps at ground level. Any woodlice you find can simply be returned to a damp, sheltered spot outside.
Frequently Asked Questions
How many legs do woodlice have?
Adult woodlice have fourteen legs, arranged in seven pairs — one pair on each of the seven segments of the main body section. Newly hatched woodlice have twelve legs and gain the final pair after their first moult.
Do all woodlouse species have 14 legs?
Yes. All adult woodlice — every species, from pygmy woodlice to giant tropical isopods — have seven pairs of walking legs. It's a defining feature of the isopod body plan.
Are woodlice insects?
No. Woodlice are crustaceans, related to crabs and shrimp. Insects have six legs and three body sections; woodlice have fourteen legs and a segmented, plated body.
How can you tell a baby woodlouse from an adult?
Count the legs. Newly released young (mancae) have six pairs rather than seven, are paler than adults, and gain their seventh pair of legs after their first moult, usually within a day or so of leaving the brood pouch.
Are woodlice harmful to humans or homes?
No. Woodlice don't bite, sting or spread disease, and they only eat decaying material — so they pose no threat to healthy plants or dry, sound timber. Indoors they're a sign of damp, not a pest problem in their own right.
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