Common pill bug vs Pill millipede
These two are easy to mix up. Here's how to tell a common pill bug from a pill millipede, and whether either one bites or stings.
Common pill bug
Armadillidium vulgare
Pill millipede
Glomeris marginata
≠The key differences
The pill woodlouse is a crustacean with 7 pairs of legs and many narrow segments ending in two short tail plates; the pill millipede has many more legs, a broad shield behind the head, a large rounded rear plate and a glossier, smoother shell.
⚖︎Side by side
| Common pill bug | Pill millipede | |
|---|---|---|
| To humans | Non-toxic | Non-toxic |
| Size | 8-15 mm long (up to about 18 mm) | 7-20 mm long (typical adult length) |
| Colours | Gray, Brown, Dark slate | Dark brown / black, Reddish brown, Pale yellow margin |
| Family | Armadillidiidae | Glomeridae |
| Habitat | Moist, shaded places: under rocks, logs, leaf litter, mulch, compost piles, and occasionally inside basements or garages. | Leaf litter, under logs and stones, mossy banks, gardens, hedgerows and woodland in temperate regions; prefers moist microhabitats. |
| Range | Originally native to Europe but now widespread across temperate regions worldwide through human-assisted dispersal. | Widespread across western and central Europe and into parts of southern and eastern Europe; commonly recorded in the British Isles and mainland Europe. |
| Active | Most active in cool, moist conditions; primarily nocturnal or active in damp daylight conditions. | Active mainly in damp conditions year-round in mild climates; most active spring to autumn and at night or during damp daylight hours. |
| 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 pill millipede
- Small, dome-shaped body that rolls into a tight ball (volvation) when disturbed.
- Glossy dark dorsal plates, each with a pale whitish or yellowish rear edge.
- Short, compact appearance with legs mostly hidden under the body when viewed from above.
- Size typically 7-20 mm; adults have a smooth, rounded outline rather than elongate cylindrical shape.
?Frequently asked questions
What is the difference between a common pill bug and a pill millipede?
The pill woodlouse is a crustacean with 7 pairs of legs and many narrow segments ending in two short tail plates; the pill millipede has many more legs, a broad shield behind the head, a large rounded rear plate and a glossier, smoother shell.
Is a common pill bug or a pill millipede more dangerous?
Common pill bug: Non-toxic. Pill millipede: Non-toxic. Pill bugs do not bite or sting and are not poisonous. Not dangerous.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.