Common pill bug vs Common shiny woodlouse
These two are easy to mix up. Here's how to tell a common pill bug from a common shiny woodlouse, and whether either one bites or stings.
Common pill bug
Armadillidium vulgare
Common shiny woodlouse
Oniscus asellus
≠The key differences
Flatter and more elongated; cannot roll into a complete ball and has a different dorsal plate shape and pattern.
A. vulgare rolls into a tight ball when disturbed; O. asellus does not.
⚖︎Side by side
| Common pill bug | Common shiny woodlouse | |
|---|---|---|
| To humans | Non-toxic | Non-toxic |
| Size | 8-15 mm long (up to about 18 mm) | 8-15 mm long |
| Colours | Gray, Brown, Dark slate | Grey, Brown, Pale cream (legs/antennae) |
| Family | Armadillidiidae | Oniscidae |
| Habitat | Moist, shaded places: under rocks, logs, leaf litter, mulch, compost piles, and occasionally inside basements or garages. | Moist, shaded microhabitats: under logs, stones, leaf litter, compost, tree bark, and inside damp basements or cellars. |
| Range | Originally native to Europe but now widespread across temperate regions worldwide through human-assisted dispersal. | Native to Europe; widely introduced across temperate regions including North America, New Zealand and elsewhere. |
| Active | Most active in cool, moist conditions; primarily nocturnal or active in damp daylight conditions. | Year-round in mild climates; most active at night and after rain |
| Pest? | No | No |
🔍How to spot a common pill bug
- Rolls into a tight ball (conglobation) when disturbed; this distinguishes pill bugs from other woodlice that cannot fully roll.
- Segmented, overlapping dorsal plates with visible antennae and seven pairs of legs when unrolled.
- Size about 8-15 mm and grey to brown mottled coloration.
🔍How to spot a common shiny woodlouse
- Smooth, shiny dorsal plates and overall glossy appearance compared with rougher-bodied species
- Size 8-15 mm, flattened oval body with 7 visible segments and rear uropods
- Cannot roll into a tight ball (unlike Armadillidium species)
- Prefers damp shaded places; often found under logs, stones and leaf litter
?Frequently asked questions
What is the difference between a common pill bug and a common shiny woodlouse?
Flatter and more elongated; cannot roll into a complete ball and has a different dorsal plate shape and pattern. A. vulgare rolls into a tight ball when disturbed; O. asellus does not.
Is a common pill bug or a common shiny woodlouse more dangerous?
Common pill bug: Non-toxic. Common shiny woodlouse: Non-toxic. Pill bugs do not bite or sting and are not poisonous. Harmless to people.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.