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Science & Nature • Invertebrates

Worm

A worm is a general term for many unrelated invertebrate animals with soft, elongated bodies, usually lacking legs and a backbone.

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

Worm is a general term for many unrelated invertebrate animals with soft, elongated bodies, usually lacking legs and a backbone. In biology, the word is not a formal taxonomic group; it is used for several different animal phyla, including flatworms, roundworms, and segmented worms. Worms are familiar to Canadian readers through soil ecology, gardening, composting, fisheries, and parasitology; earthworms are especially important in Canadian soils and decomposition processes.

Biological use of the term

In biology, worm is a descriptive common name, not a formal classification. It is applied to several distantly related invertebrate groups that share a similar body form.

Major worm groups

The term covers several phyla, including flatworms, segmented worms, roundworms, ribbon worms, and others. These groups differ widely in anatomy, ecology, and life cycle.

Shared features

Worms are typically soft-bodied, elongated, and legless, and many live in soil, water, or as parasites. Some groups have well-developed body segments, while others do not.

Other meanings

Outside zoology, worm can also refer to certain larval insects, a computer worm, or figurative uses in language. These are separate from the biological sense.

Key facts

  • The word worm refers to many unrelated animals rather than one single biological group.
  • Most worms are invertebrates with long, soft bodies and no limbs.
  • Common worm groups include Platyhelminthes (flatworms), Nematoda (roundworms), and Annelida (segmented worms).
  • Some animals called worms are not invertebrates, such as caecilians and slow worms, which are not true worms in the strict biological sense.
  • The term also has other meanings in computing, where a worm is a self-replicating program.
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Canadian context

Worms are familiar to Canadian readers through soil ecology, gardening, composting, fisheries, and parasitology; earthworms are especially important in Canadian soils and decomposition processes.

Frequently asked questions

Is a worm a single scientific animal group?
No. Worm is a common descriptive term for several unrelated invertebrate groups, not a single formal taxon.
What animals are called worms?
Examples include earthworms, flatworms, roundworms, ribbon worms, and leeches, among others.
Are all worms invertebrates?
Most are, but the term is also sometimes used for animals like caecilians and slow worms, which are not true worms biologically.
Do worms all look the same?
No. They share a generally elongated, soft body plan, but their anatomy and lifestyles vary widely.
Does worm have meanings outside biology?
Yes. It can also mean a self-replicating computer program, among other non-biological uses.

References

  1. Britannica — https://www.britannica.com/animal/worm
    Supports: Defines worm as a general term for various unrelated invertebrate animals and lists major groups.
  2. Britannica Kids — https://kids.britannica.com/kids/article/worm/353935
    Supports: Explains that worms are soft-bodied invertebrates, not all related, and gives broad group examples.
  3. Encyclopedia.com — https://www.encyclopedia.com/plants-and-animals/animals/zoology-invertebrates/worm
    Supports: States worms are various creeping or burrowing invertebrates and notes common groupings.
  4. University of Hawaiʻi — https://manoa.hawaii.edu/exploringourfluidearth/biological/invertebrates/worms-phyla-platyhelmintes-nematoda-and-annelida
    Supports: Describes worms as several distinct phyla with bilateral symmetry and basic body-plan traits.