What are spiders?

Wherever you live, you're always close to a spider. 

Diagram of Male Spider, view from above

 © Australian Museum

Find out what spiders are, where they came from and how they got around, as well as Australia's own diverse spider fauna. Spiders are arachnids not insects, but both spiders and insects belong to the largest group of animals on Earth, the arthropods (Ancient Greek: arthro = joint, podos = footed) - animals with hard external skeletons and jointed limbs .

What are the differences between spiders and insects?

Spiders have;

  • two main body parts,
  • eight walking legs,
  • simple eyes
  • piercing jaws (fangs),
  • abdominal silk spinning organs,
  • anterior abdominal genital opening.

Insects have three main body parts, six walking legs, compound eyes, antennae, chewing jaws (mandibles - often secondarily modified), posterior abdominal genital opening.

Relatively speaking - the Arachnida

Spiders and their relatives are called arachnids. Arachnids have the head and thorax combined (cephalothorax) with simple eyes, jaws adapted for tearing or piercing prey, a pair of pedipalps and eight walking legs.

Arachnids include spiders, scorpions, pseudoscorpions, amblypygids( tailless-whipscorpions), schizomids (micro-whipscorpiones), palpigrades, harvestmen, ticks and mites.

Spiders are the only arachnids that have special glands in their abdomen which produce silk

Midgets to monsters

A few spiders are so small and live such hidden lives that most of us never see them. Others are enormous.

Some of the smallest spiders in the world are anapid spiders, sometimes called armoured spiders because of the cuticular plates on their pinhead-sized bodies. Small spiders like anapids are usually found in damp, cool habitats like forest leaf litter and moss because their small bodies can lose water rapidly in dryer conditions. The largest spiders in the world include the South American Goliath Tarantula, some so big their legs can span a dinner plate. Such spiders may take decades to reach such a size. However, spider size is limited, partly because their respiratory physiology becomes less efficient at very large sizes.

Bodies bizarre

Many spiders have unusual body shapes and colours.

Bizarre bodies can be helpful to spiders in various ways - to deceive and ambush prey, to capture particular sorts of prey, to avoid being eaten and to attract mates.

 

Do you have a question or comment? Please contact our Search & Discover team.


Dr Mike Gray
Last Updated:

Tags arachnids, invertebrates, what is a spider, spiders,