Pill bugs fact sheet
What are pill bugs?
Pill bugs are a type of crustacean called isopods. They are not actually bugs and are more closely related to shrimp and lobsters.
Pill bugs have an outer carapace that looks like armour and can vary in colour from white to dark grey. They can grow up to 2 centimetres long.
Pill bugs differ from other land living isopods as they can roll into a tight ball. They roll into a ball to protect their soft body parts from predation or drying out. Because they can roll into a ball, pill bugs are also often called 'roly polies'.
Pill bugs are not native to Australia and originally come from Europe. However, pill bugs are now found all across Australia.
Fast facts – Pill bugs
What are they – Pill bugs are crustaceans called isopods; they are not true bugs and are more closely related to shrimp and lobsters.
Body features – They have an armoured outer carapace and can grow up to 2 centimetres long. Pill bugs can roll into a tight ball to protect their soft body parts from predators or drying out.
Diet – Pill bugs help clean up the environment by recycling and decomposing old plant and animal matter.
Where they live – Pill bugs live in wet or damp environments because they have gills and need to stay moist to breathe. They are commonly found under logs and rocks and among decaying vegetation, especially where the underside is damp.
Life cycle – Female pill bugs carry their eggs in a pouch under their body. Baby pill bugs hatch in their mother’s pouch and stay there until they are big enough to live independently.
Where do pill bugs live?
Pill bugs live in wet or damp environments. Pill bugs have gills and need to stay moist so they can breathe.
Pill bugs can be found under logs and rocks and amongst decaying vegetation.
What are the external features of pill bugs?
Pill bugs are often confused with pill millipedes as they are both similar in size and live in similar habitats. Like all millipedes, pill millipedes have two pairs of legs per body segment. Pill bugs only have one pair per body segment.
Cephalothorax
The head and first segment of the thorax are joined together. This is called the cephalothrax.
Thorax
The thorax includes the region between the second and seventh segment. This region is called the pereon.
The hard exoskeleton has seven armoured plates which protect the body. They are made of chitin.
Abdomen
The abdomen is made up of five condensed segments called the pleon.
Two tail-like ‘uropods’ can be found at the end of their bodies. Uropods help pill bugs to find their way around
What do pill bugs eat?
Pill bugs eat algae, moss, bark and fungi.
Pill bugs are also detritivores, meaning they eat decaying plant and animal material.
What role do pill bugs play in the ecosystem?
Pill bugs clean up the environment by helping to recycle and decompose old plant and animal matter. When pill bugs feed they help increase nutrients and minerals and remove toxins in the soil. Improved soil quality helps plant growth.
What eats pill bugs?
Centipedes, spiders, ants, birds and amphibians are known predators of pill bugs.
How do pill bugs reproduce and grow?
Like many other invertebrates, pill bugs start their life as an egg and must moult to grow.
Egg
Pill bugs start their life as an egg. Female pill bugs carry their eggs in a pouch under their body.
Pill bug eggs
Hatched young
Baby pill bugs hatch in their mother's pouch and stay there until they are big enough to be on their own.
A female pill bug carries her young in a pouch under her body.
Moulting
As pill bugs grow they shed their exoskeleton in a process called moulting. A new exoskeleton grows beneath the old one which eventually splits into two pieces.
A young pill bug which has not fully grown yet
Adult
A pill bug moults about 5 times until it is full-grown.
Related fact sheets
More invertebrate fact sheets
- Invertebrate fact sheets – overview
- Crustaceans fact sheet – broader group including pill bugs, slaters and other isopods.
- Millipede fact sheet – compares pill bugs with pill millipedes and other decomposers in leaf litter.
- Centipede fact sheet – predator of pill bugs in soil and leaf litter.
- Earthworms fact sheet – other soil and litter decomposers that recycle nutrients.
Habitats and ecosystems
Attributions
References
Backyard Buddies. n.d. Slaters. [online] Foundation for National Parks & Wildlife. Available at: <https://backyardbuddies.org.au/backyard-buddies/slaters/>.
Cassidy, J. 2017. Pill bugs emerged from the sea to conquer the Earth. [online] PBS News Hour. Available at: <https://www.pbs.org/newshour/science/pill-bugs-emerged-sea-conquer-earth>.
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title
Pill bugs fact sheet
description
Learn about pill bugs, or ‘roly polies’, land-living crustaceans that can roll into a tight ball for protection. This student-friendly fact sheet explains what pill bugs are, how they differ from pill millipedes, where they live under damp logs and leaf litter, what they eat as detritivores, how they help recycle nutrients and improve soil, and their life cycle from egg in a brood pouch to juvenile to moulting adult. Created by Field of Mars EEC.
published-time
2025-07-23T06:33:45.842Z
modified-time
2025-07-23T06:33:45.842Z