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Crab spider

Crab spider is a common name for a group of spiders, most often members of the family Thomisidae, named for their crab-like body shape and sideways movement.

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

Crab spider is a common name for a group of spiders, most often members of the family Thomisidae, named for their crab-like body shape and sideways movement. They are ambush predators that do not build capture webs and are generally harmless to humans. Crab spiders occur worldwide and many species live on flowers, leaf litter, or bark.

Taxonomy and naming

Crab spider is a common name most often applied to the spider family Thomisidae. The name reflects their crab-like appearance and movement, including the way many species hold their front legs outward and can move sideways.

Appearance and behaviour

These spiders usually have a flattened, wide body and long front legs. They do not use webs to capture prey; instead, they hide and ambush insects that come close.

Habitat and distribution

Crab spiders are found worldwide in many habitats, including flowers, shrubs, leaf litter, soil surface, and under bark. Some species are especially associated with flowering plants.

Ecological role

Crab spiders help control insect populations by preying on many small arthropods. Species that hunt in flowers may take bees, flies, butterflies, and other visiting insects.

Key facts

  • Crab spiders are ambush predators that do not build webs to catch prey.
  • They are named for their crab-like posture, broad body, and sideways movement.
  • Many species live on flowers and feed on insects such as flies, bees, and other small arthropods.
  • Some species can change color to blend with flowers or other surroundings.
  • Crab spiders are generally not dangerous to humans.
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Canadian context

Crab spiders are found in Canada, including Quebec and other regions, and are part of the country’s native spider fauna. They are beneficial predators in gardens and natural habitats.

Frequently asked questions

What is a crab spider?
A crab spider is a spider, usually in the family Thomisidae, named for its crab-like body shape and sideways movement.
Do crab spiders spin webs to catch prey?
No. Crab spiders usually hunt by ambush and do not build webs to trap prey.
Are crab spiders dangerous to humans?
They are generally harmless to humans, and their venom is not considered dangerous.
Why are they called crab spiders?
They are named for their crab-like appearance and the way many species can move sideways or backward.
Where do crab spiders live?
They are found worldwide in habitats such as flowers, leaf litter, soil surfaces, and under bark.

References

  1. Encyclopaedia Britannica — https://www.britannica.com/animal/crab-spider
    Supports: Family Thomisidae, crab-like shape, worldwide distribution, ambush hunting
  2. Terminix — https://www.terminix.com/spiders/crab/
    Supports: Identification, appearance, movement, size, and general behaviour
  3. Montana State University Urban IPM — https://urbanipm.montana.edu/entomology/resources/fact-sheets/spiders_of_montana/crab.spider.html
    Supports: Ambush hunting, lack of capture webs, harmlessness, beneficial role
  4. Espace pour la vie — https://m.espacepourlavie.ca/en/insects-arthropods/crab-spiders
    Supports: Size range, species count, distribution, harmlessness, ecological role
  5. University of Florida IFAS — https://entnemdept.ufl.edu/projex/gallery/dl/Beneficial_Arthropods_Predators/text/crab_spiders.htm
    Supports: Flower association, prey types, and presence in the United States and Canada