Important Features of Spider Biology

How do spiders differ from insects?

Spiders are characterized by:

  • Two body parts
  • Eight legs
  • Chelicerae or fangs
  • No wings
  • No antennae

Insects are characterized by:

  • Three body parts
  • Six legs
  • Mandibles
  • Wings
  • Antennae

What traits are typical of spiders?
Silk, pedipalps, external digestion, poison glands

Where are spiders found?
Everywhere but the ocean, and Antarctica

What do spiders eat?
All spiders are predators. Do not eat plants but other living animals.

  • Insects
  • Spiders
  • Invertebrates
  • Some small vertebrates.

How do they eat?
Venom to kill or paralyze prey from hole in fangs (chelicerae), external digestion with digestive enzymes acting outside of body to liquify prey.

How do they grow?
Exoskeleton (external skeleton) must be shed or moulted.  Moulting is a very important and risky part of life for spiders.

How does silk work?
Silk is strong but flexible.  Webs are enlargements of the spider’s sensory system. Slows down & entangles prey.  Mechanics of the orb web.

How do spiders have sex?
Carefully! Females will sometimes eat the male. Male’s anatomy and courtship behavior adapted to surviving mating. Spiders have unique anatomy for internal fertilization.

Are many spiders poisonous to humans?
No! Most are too small to bite through skin, venom not adapted to humans, too little venom, not in same place as humans. All bites have 2 fang marks.  In US, only four groups are poisonous:

  • Black widow
  • Brown recluse
  • Hobo spider
  • Yellow sac spider*.

What is closely related to spiders?
Spiders are arachnids. Other arachnids are scorpions, whip scorpions or vinegaroons, tailless whip scorpions, harvestmen or daddy-long-legs, mites/ ticks, solfugids or ‘sun spiders’, and pseudoscorpions. The closest relative of the arachnids are horseshoe crabs – count their legs, body parts, and look at their chelicerae.