Pill bugs

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.

An uncurled pill bug showing its many legs and antennae.

Pill bugs roll into a tight ball to protect themselves.

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.

Logs create habitat for some invertebrates. The underside of the log is usually damp, needed by pill bugs as they breathe through gills.

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

Pill bugs have a cephalothorax, thorax and abdomen. The hard exoskeleton of a provides protection from predators.

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.

Rotting leaf litter is a good source of food for pill bugs.

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.

Pill bugs help to break down and recycle dead plant material such as logs and leaf litter.

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.

Adult pill bug

Invertebrate explorer digital book

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Written by teachers, the invertebrate explorer digital book explores the incredible world of Australian invertebrates.

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