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Isopod

An isopod is any crustacean in the order Isopoda.

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

An isopod is any crustacean in the order Isopoda. Isopods include marine, freshwater, and terrestrial species such as woodlice, pill bugs, and gribbles, and they occur worldwide in many habitats. The group is highly diverse in form and ecology, with some species free-living and others parasitic.

Classification and diversity

Isopods are an order within the crustaceans, specifically Malacostraca. Sources estimate roughly 10,000 described species, and the group is divided into multiple suborders.

Body plan and biology

Isopods typically have a flattened segmented body, two pairs of antennae, and seven pairs of thoracic legs. Females brood their young in a ventral pouch called a marsupium.

Habitats and ecology

Isopods occur in oceans, freshwater systems, soil, caves, aquifers, and other terrestrial habitats. Most are scavengers, detritus feeders, or omnivores, while some species are parasitic on other animals.

Common names and familiar species

Terrestrial isopods such as woodlice, pill bugs, sowbugs, and roly-polies are the best-known examples for many people. Marine relatives include gribbles and many deep-sea forms.

Key facts

  • Isopods are crustaceans in the order Isopoda.
  • They live in marine, freshwater, and terrestrial environments.
  • Many species are free-living, but some marine isopods are parasitic.
  • They are usually dorsoventrally flattened and have seven pairs of walking legs.
  • Well-known terrestrial isopods include woodlice and pill bugs.
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Canadian context

Isopods are familiar to Canadian readers through terrestrial woodlice and pill bugs found in moist soil and leaf litter, and through marine species in Atlantic, Pacific, and Arctic coastal waters.

Frequently asked questions

What is an isopod?
An isopod is a crustacean belonging to the order Isopoda.
Are isopods insects?
No. Isopods are crustaceans, not insects.
Where do isopods live?
They live in marine, freshwater, and terrestrial habitats, including soils, caves, aquifers, and the deep sea.
How many species of isopods are there?
Sources estimate about 10,000 described species.
What are some common isopods?
Common examples include woodlice, pill bugs, sowbugs, and gribbles.
Are all isopods free-living?
No. Many are free-living, but some marine species are parasitic.

References

  1. Encyclopaedia Britannica — https://www.britannica.com/animal/isopod
    Supports: Defines isopods as crustaceans in the order Isopoda and notes their marine, freshwater, and terrestrial diversity.
  2. Wikipedia — https://en.wikipedia.org/wiki/Isopoda
    Supports: Provides body-plan details including segmentation, antennae, seven pairs of legs, and brood pouch.
  3. WoRMS / MarineSpecies.org — https://www.marinespecies.org/isopoda/
    Supports: Gives species estimates, habitat range, size range, and common names.
  4. Encyclopedia.com — https://www.encyclopedia.com/plants-and-animals/animals/zoology-invertebrates/isopods
    Supports: Summarizes classification, flattened body form, habitats, ecology, and the approximate number of known species.
  5. NOAA — https://www.noaa.gov/ocean-fact/isopod/
    Supports: States that isopods are crustaceans, widely distributed, morphologically diverse, and found in many habitats.
  6. South Carolina Department of Natural Resources — https://www.dnr.sc.gov/marine/sertc/Isopod%20Crustaceans.pdf
    Supports: Describes isopod features, habitats, common examples, and approximate species count.