Spiders, scorpions and mites are not insects but arachnids. Insects have three pairs of legs and three body sections, while arachnids have four pairs of legs and two body sections. They also have two grasping “limbs” called pedipalps. Spiders have many pairs of eyes. All spiders can produce silk, but only some kinds use it for spinning sticky webs to trap flying insects.

Spider silk

A spider makes silk from a liquid produced by glands inside its abdomen. As the silk is drawn out of the spider’s body through the spinnerets, it becomes a solid thread. The spider pulls the silk out using the claws on its back legs. Besides making webs, spiders use their silk to wrap up their prey when captured, to cocoon their eggs, as a safety line, and even as a parachute to float in the wind.

Webs

Many spiders catch their prey by spinning webs. These can be of a great variety of shapes, including delicate spirals, irregular cobwebs or thick funnels. Once an insect is caught in the web, the spider can tell exactly where it is by feeling the vibrations using the hairs on its legs. It then hurries to claim its victim. The spider may wrap it, dead or alive, in a cocoon of silk. It can then be stored for eating later.

The orb spider, often found in gardens, spins webs like these, pictured left. They usually only last until the evening before the spiders eat and recycle them. It can take as little as an hour for the spider to make a new one.

Feeding

Spiders feed by piercing their victim with their sharp fangs and injecting venom (poison). This paralyses or kills the prey. The spider's saliva turns the body tissues of the prey into liquid. The spider then sucks this liquid up. Most spiders are completely harmless to humans, but the bite of some species, such as the black widow, can be fatal.

Jumping spider

There are thousands of kinds of jumping spider. These tiny spiders do not spin webs, but jump to catch their prey. They use their sharp fangs to inject venom into their victim. They often eat moths or flies, but some will attack creatures bigger than themselves, such as mantises.

Tarantulas are mostly large, hairy spiders. The biggest tarantulas, the bird-eating spiders, can have leg spans of up to 30 centimetres (12 inches)—as wide as a dinner plate. Despite their name, they usually eat beetles, grasshoppers and small reptiles. They are found in the rainforests of South America.

A tarantula’s fangs are folded up just below its eyes. They are hollow and contain venom glands. They are used to inject venom into both prey or attackers. Its mouth is like a straw: it can only suck juices. So anything the spider eats must be turned to liquid first of all. Large prey, such as rodents, must first be crushed, ground up and and coated with digestive juices.