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Science & Nature • Crustaceans

Pill bug

Pill bugs are small land-dwelling crustaceans in the order Isopoda, commonly known for their ability to roll into a tight ball when disturbed.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

Pill bugs are small land-dwelling crustaceans in the order Isopoda, commonly known for their ability to roll into a tight ball when disturbed. They are not insects or true bugs, and are closely related to other crustaceans such as crabs, shrimp, and lobsters. In Canada, they are familiar in gardens, lawns, and damp outdoor habitats, where they are often seen under rocks, logs, and mulch.

Classification

Pill bugs are terrestrial crustaceans in the order Isopoda. They are not insects, despite their common name, and are more closely related to crabs and shrimp than to insects.

Appearance and behaviour

Pill bugs are small, oval-bodied animals with segmented backs and multiple pairs of legs. When threatened, many species can curl into a tight ball as a defensive response.

Habitat and diet

They live in damp, shaded places such as leaf litter, mulch, and under stones or logs. They feed mainly on decomposing plant material and other organic debris.

Ecological role

Pill bugs act as decomposers and contribute to nutrient recycling in soil. Their activity helps break down organic matter in garden and forest ecosystems.

Key facts

  • Pill bugs are crustaceans, not insects or true bugs.
  • Their ball-rolling defense is the source of the common name “pill bug.”
  • They are adapted to life on land but usually require moist environments.
  • They feed mainly on decaying organic matter and help recycle nutrients in soil.
  • The common species often referenced as the pill bug is *Armadillidium vulgare*.
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Canadian context

Pill bugs are familiar in Canadian gardens, lawns, and damp outdoor habitats, where they are often seen under rocks, logs, and mulch.

Frequently asked questions

Are pill bugs insects?
No. Pill bugs are crustaceans in the order Isopoda, not insects.
Why are they called pill bugs?
They are named for their ability to roll into a pill-like ball when disturbed.
What do pill bugs eat?
They mainly eat decaying plant material and other organic matter.
Where do pill bugs live?
They prefer moist, shady habitats such as leaf litter, mulch, rocks, and logs.
Are pill bugs harmful to people?
They do not bite or sting and are generally harmless to people.
What is the scientific name of the common pill bug?
The commonly cited species is *Armadillidium vulgare*.

References

  1. Field of Mars EEC — https://fieldofmar-e.schools.nsw.gov.au/fact-sheets/invertebrates/pill-bugs-fact-sheet
    Supports: Pill bugs are land-living crustaceans in the order Isopoda and can roll into a tight ball.
  2. University of California Agriculture and Natural Resources IPM — https://ipm.ucanr.edu/home-and-landscape/pillbugs-and-sowbugs/
    Supports: Pillbugs are soil-dwelling crustaceans in the order Isopoda and feed primarily on decaying plant material.
  3. National Institute of Environmental Health Sciences — https://kids.niehs.nih.gov/topics/natural-world/wildlife/ecology/pills
    Supports: Pillbugs are crustaceans rather than insects and are land-dwelling relatives of crayfish and shrimp.
  4. WebMD — https://www.webmd.com/a-to-z-guides/what-to-know-about-pill-bugs
    Supports: Pill bugs are widespread, live in moist shady environments, and help recycle decaying matter.
  5. Wikipedia — https://en.wikipedia.org/wiki/Armadillidiidae
    Supports: Armadillidiidae is the family containing pill bugs and members can roll into a ball.