Woodlice are properly remarkable little crustaceans — found under stones, logs, and leaf litter throughout the UK and properly across most of the world. This guide covers identification of the most common UK species, their habits, breeding, ecological role, and the genuinely interesting facts that make these terrestrial crustaceans worth knowing properly.
What Is "The Common Woodlouse"?
Properly worth clarifying the terminology. In UK usage, "the common woodlouse" can refer to several species:
- Common Shiny Woodlouse (Oniscus asellus) — smooth, glossy grey-brown body with yellow patches, 12-16mm. Properly the most commonly seen UK species in gardens
- Common Rough Woodlouse (Porcellio scaber) — properly textured, bumpy grey body, 12-17mm. Distinguished by its rough surface (hence the name)
- Common Pill Bug (Armadillidium vulgare) — capable of rolling into a ball, 12-18mm, dark grey-brown
Properly the article covers identification of all three plus other UK natives, since "the common woodlouse" depends on regional usage.
Quick Identification Guide
Common Shiny Woodlouse (Oniscus asellus)
- Body texture: Smooth and glossy
- Colour: Grey-brown with yellow patches along sides
- Size: 12-16mm
- Habitat: Damp gardens, under stones, leaf litter
- Behaviour: Properly active, doesn't roll into a ball
Common Rough Woodlouse (Porcellio scaber)
- Body texture: Bumpy/granular (the rough texture is properly diagnostic)
- Colour: Grey, sometimes with brown or yellow tinges
- Size: 12-17mm
- Habitat: More tolerant of drier conditions than O. asellus; found under bark, in stone walls
- Behaviour: Doesn't roll; faster moving than many species
- Hobby relevance: Properly the species from which many hobby morphs originate (Lava, Orange Dalmatian, Spanish Orange, Koi, Pied)
Browse our Porcellio collection for hobby morphs of this species.
Common Pill Bug (Armadillidium vulgare)
- Body texture: Smooth, distinctly domed/convex shape
- Colour: Dark grey-brown, various morphs in hobby
- Size: 12-18mm
- Habitat: Drier conditions than other species; calcareous soils preferred
- Behaviour: Conglobates (rolls into ball) when disturbed — properly the iconic woodlouse behaviour
- Hobby relevance: Source of many premium morphs (Magic Potion, T+ Albino, High Yellow, Mosaic)
Browse our Armadillidium collection for hobby morphs.
Common Striped Woodlouse (Philoscia muscorum)
- Body texture: Smooth
- Colour: Mottled yellowish-brown with distinct dark stripe down the back, black head
- Size: 8-11mm
- Habitat: Leaf litter, wood piles, grasslands
- Behaviour: Properly known for speed — quickly scuttles away when disturbed
Common Pygmy Woodlouse (Trichoniscus pusillus)
- Body texture: Soft, slightly flexible
- Colour: Reddish-brown
- Size: 3-5mm (one of the smallest UK species)
- Habitat: Damp leaf litter, under loose bark
- Behaviour: Easily overlooked due to small size
Body Structure: Properly More Complex Than It Looks
Woodlice are properly built more elaborately than their appearance suggests:
- Total segments: 13 (7 pereon + 6 pleon)
- Leg-bearing segments: The 7 pereon (thoracic) segments each carry a pair of jointed legs
- Total legs: 14 (7 pairs)
- Pleon segments: 6 smaller abdominal segments containing pleopodal lungs and reproductive structures
- Antennae: One conspicuous pair plus one smaller barely-visible pair
- Eyes: Compound eyes on the head, properly less complex than insect compound eyes
Properly worth noting: the exoskeleton isn't fully waterproof — this is why woodlice need humid environments and hide during dry/sunny periods. For more anatomy detail see our are isopods insects article.
Properly Genuine Interesting Facts
They're Crustaceans, Not Insects
Properly the most fundamental fact. Woodlice are crustaceans (Class Malacostraca, Order Isopoda, Suborder Oniscidea), making them more closely related to crabs, lobsters, and shrimp than to insects. They're the only fully terrestrial crustacean lineage with global distribution.
They Excrete Ammonia Directly
Unlike most terrestrial animals which convert nitrogenous waste to urea or uric acid (which is properly safer to handle), woodlice excrete ammonia directly through their exoskeleton. In dense groups this can produce a distinctive smell — earning them nicknames like "stinky pigs" in some regions.
They Can Drink Through Their Tail-End
Properly unusual detail. Woodlice can absorb water through specialised pleopodal lungs on the underside of their abdomen. They can also drink through their mouthparts (anteriorly) but the posterior absorption is properly characteristic.
They Carry Their Young in a Pouch
Female woodlice carry fertilised eggs in a marsupium (brood pouch) formed by overlapping plates on the underside of the body. Properly fascinating because:
- The marsupium contains fluid that supports development
- Embryos receive water and oxygen from the mother
- Brood time properly varies by species: typically 21-45 days for A. vulgare
- Young emerge as miniature versions of adults (called mancae)
Mancae Hatch Without Their Last Pair of Legs
Properly distinctive isopod feature. When mancae emerge from the marsupium, they have only six leg-bearing segments instead of the adult's seven. The seventh pair develops after their first moult, properly adding to the body complexity gradually.
They Were Once Marine
Properly worth knowing for evolutionary context. Woodlice descended from marine isopods that transitioned to land roughly 300 million years ago (during the Carboniferous period). The transition required evolving:
- Pleopodal lungs from gills
- Water-conserving exoskeleton (though properly imperfect — they still need humidity)
- Brood pouch reproduction (vs. releasing eggs into water)
- Terrestrial locomotion adaptations
For more on the life cycle see our comprehensive woodlouse life cycle guide.
Some Species Survive Brief Immersion
Sea slaters (Ligia oceanica) inhabit coastal splash zones and survive brief immersion in seawater. Properly worth being clear: they're still air-breathing — they don't extract oxygen from water like fish or marine isopods. They're properly adapted to wet but not submerged conditions.
They Eat Their Own Faeces
Properly counterintuitive but true. Woodlice practice coprophagy (consuming their own droppings) to recover nutrients from incompletely digested material. Properly especially important for copper, which is essential for their hemocyanin (blood pigment) but difficult to obtain.
They Roll Into a Ball (Some Species)
Conglobation (rolling into a ball) is properly the iconic woodlouse defence — but NOT all species do it. Only certain families (mainly Armadillidiidae and Cubaris) can fully conglobate. UK natives that roll include A. vulgare and related species. Non-rollers (Porcellio, Porcellionides, Oniscus, Philoscia) properly flatten or run instead.
They Carry Their Calcium Stores
Properly important fact for hobby keepers. Woodlice store calcium in their exoskeleton, requiring constant access to calcium-rich material for shell health. In gardens they get this from limestone, weathered concrete, and dead snail shells. In hobby setups cuttlebone is properly the standard.
Habitat and Behaviour
Where They Live
Woodlice are properly nocturnal (active mainly at night) and prefer damp, dark environments. UK habitats include:
- Under stones, logs, and decaying wood
- In leaf litter and compost heaps
- Beneath loose tree bark
- In stone walls (especially mortar gaps)
- Greenhouse and cellar environments
- Coastal splash zones (specialist species)
Daily Cycle
- Day: Sheltering in moisture-retaining locations
- Dusk and night: Properly active, foraging for decaying matter
- Dawn: Return to sheltered locations
This avoidance of bright light and dry air properly reflects their imperfect water conservation and ectothermic biology.
Diet: Why They Matter Ecologically
Woodlice are properly detritivores — feeders on decaying organic matter. Diet includes:
- Decaying leaves (the staple)
- Decaying wood
- Fungi and moulds
- Decaying plant matter
- Occasional protein from dead invertebrates
- Calcium-rich materials (snail shells, weathered limestone)
Their ecological contribution is properly significant:
- Accelerate decomposition of plant matter
- Return nutrients to soil through frass
- Distribute fungal spores and beneficial bacteria
- Form prey base for many predators
- Indicate healthy soil ecosystem when abundant
UK Distribution and Conservation
The common UK woodlouse species are properly:
- Not endangered — populations stable across the UK
- Widespread — found throughout the British Isles in suitable habitat
- Indicator species — abundance reflects soil ecosystem health
- Globally distributed — humans have inadvertently transported them to every continent except Antarctica
Conservation concerns properly focus on broader habitat protection (gardens, woodland, soil ecosystems) rather than direct species protection.
Common Names Across Regions
Woodlice have properly remarkable linguistic diversity:
UK Regional Names
- Cheeselog/Cheesy bug — southern England (especially Berkshire/Reading)
- Chucky pig — parts of England
- Granny grey — some regional UK use
- Pill bug — for conglobating species specifically
- Mochyn coed — Welsh, literally "wood pig"
International Names
- Slater/Slater bug — Australia and New Zealand
- Sow bug — North America
- Roly-poly/Pill bug — North America
The Hobby Connection
UK keepers properly often start their isopod hobby with garden-collected common UK natives before moving to hobby species. The transition properly involves:
- Standard UK species (P. scaber morphs, O. asellus) — easy starting point
- European hobby species (Powder morphs, Dairy Cow, Zebra) — visually striking
- Tropical premium species (Cubaris, Ardentiella) — advanced
Browse our isopods collection for the UK hobby range, or start by observing wild common UK species in your garden — properly genuinely interesting in their own right.
The Honest Summary
The "common woodlouse" you find in UK gardens is most likely one of three species:
- Common Shiny Woodlouse (O. asellus) — smooth, glossy, yellow patches
- Common Rough Woodlouse (P. scaber) — bumpy texture, grey body
- Common Pill Bug (A. vulgare) — domed shape, rolls into a ball
All three are properly fascinating in their own right. They're crustaceans (not insects), have 13 body segments and 14 legs, breathe through pleopodal lungs, carry their young in a marsupium, and play essential ecological roles in soil ecosystems. Their nocturnal habits, calcium dependency, and ammonia excretion are properly distinctive features worth knowing.
Whether you're observing wild UK garden species or keeping hobby morphs, woodlice properly reward closer attention. Browse our isopods collection for the UK hobby range.
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