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Pill bugs

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 two 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.

Pill bug with segmented body
Image: An uncurled pill bug showing its many legs and antennae.
Pill bug in the shape of a small ball
Image: Pill bugs will 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.

Hollow log
Image: 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.

Pill bug with segmented body
Image: The hard exoskeleton of a pill bug provides protection from predators.

Pill bug head
Image: Pill bug cephalothorax

Cephalothorax

The head and first segment of the thorax are joined together. This is called the cephalothrax.

Close-up of thorax with segments
Image: Pill bug thorax

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.

 

Close up of abdomen with narrow segments
Image: Pill bug abdomen

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.

Pill bug in soil and decaying vegetation
Image: Pill bugs will look for food in the place where they live. Rotting leaf litter is a good source of food.

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.

Rotting log on forest floor.
Image: 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.

Round jelly-like pill bug eggs
Image: Pill bug eggs

Egg

Pill bugs start their life as an egg. Female pill bugs carry their eggs in a pouch under their body. 

Eggs on the underbelly of a female pill bug
Image: A female pill bug carries her young in a pouch under her body.

Hatched young

Baby pill bugs hatch in their mother's pouch and stay there until they are big enough to be on their own.

Pale coloured soft-shelled pill bug
Image: A young pill bug which has not fully grown yet

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. 

Adult pill bug with shiny hard exoskeleton
Image: Adult pill bug

Adult

A pill bug moults about five times until it is full-grown.

Invertebrate explorer book
Image: Invertebrate explorer digital book

Find out more

The invertebrate explorer digital book explores the incredible world of Australian invertebrates.

Students can use the book to investigate classification, features, adaptations and habitats of a variety of Australian invertebrates through narrated videos, stunning images, interactive activities and detailed text.

This book was designed by teachers to support the NSW Science and Technology K-6 syllabus and NSW English K-6 syllabus.

Content supports living world, Australian animals and class studies on invertebrates.

Download for free from Apple Books.

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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