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spider
Table of Contents
  • Introduction
  • General features
    • Size range
    • Distribution
    • Importance
  • Form and function
    • External features
    • Internal features
      • Nervous system and senses
      • Digestion and excretion
      • Respiration
      • Circulation
      • Reproductive system
    • Specialized features
      • Venom
      • Silk
  • Natural history
    • Reproduction and life cycle
      • Courtship
      • Mating
      • Eggs and egg sacs
      • Maturation
    • Feeding behavior
      • Stalking prey
      • Spider webs
  • Classification
    • Distinguishing taxonomic features
    • Annotated classification
References & Edit History Quick Facts & Related Topics
Images & Videos
Curtain web spider
Witness an orb-weaving spider using silk wrappings to immobilize grasshopper prey
Arachnid heavyweight Gentle giantess spider Water spider
Do we really swallow spiders in our sleep?
Black widow spider
Know how some spiders walk on the surface of the water
Keen eyesight
For Students
default image
spider summary
Quizzes
Sea otter (Enhydra lutris), also called great sea otter, rare, completely marine otter of the northern Pacific, usually found in kelp beds. Floats on back. Looks like sea otter laughing. saltwater otters
Animal Group Names
Lion (panthera leo)
Deadliest Animals Quiz
Mute swan with cygnet. (birds)
Match the Baby Animal to Its Mama Quiz
Green tree python snake (Chondropython viridis) in a rainforest.
Creepy Crawlers Quiz
vulture. An adult bearded vulture at a raptor recovery center. The Gypaetus barbatus also known as the Lammergeier or Lammergeyer, is a bird of prey and considered an Old World vulture.
Animal Factoids
Science Bugs, Mollusks & Other Invertebrates Arachnids

Internal features

in spider in

Form and function

Also known as: Araneae, Araneida
Written by
Joseph Culin
Professor of Entomology, Clemson University, South Carolina.
Joseph Culin ,
Lorna R. Levi
Coauthor of A Guide to Spiders and Their Kin; cotranslator and coeditor of Invertebrate Zoology by A. Kaestner.
Lorna R. Levi •All
Fact-checked by
The Editors of Encyclopaedia Britannica
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.
The Editors of Encyclopaedia Britannica
Last Updated: Jul 25, 2025 • Article History

News •

New research hints: Spiders came from the sea • July 24, 2025, 1:44 AM ET (Jerusalem Post)
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Culin, Joseph, Levi, Lorna R., Levi, Herbert W.. "spider". Encyclopedia Britannica, 25 Jul. 2025, https://www.britannica.com/animal/spider-arachnid. Accessed 25 July 2025.
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External Websites
  • AZ Animals - Spider
  • Arizona-Sonora Desert Museum - Spiders
  • Australian Museum - What is a spider?
  • Better Health Channel - Spiders
  • University of Minnesota Extension - Spider
  • University of Wisconsin-Madison - Wisconsin Horticulture Division of Extension - Garden Spiders
  • Burke Museum - Spider Myths
  • University of Missouri Extension - Spiders
  • Cell Press - Current Biology - The global spread of misinformation on spiders
Britannica Websites
Articles from Britannica Encyclopedias for elementary and high school students.
  • spider - Children's Encyclopedia (Ages 8-11)
  • spider - Student Encyclopedia (Ages 11 and up)