There are more than 37,000 species of spiders worldwide, but they all share the same basic features, including eight legs, two body segments (the cephalothorax and abdomen), an exoskeleton, silk glands and fangs. They belong to the Arachnid group along with ticks, mites and scorpions. Spiders are not insects.
Spiders live on every continent except Antarctica, and they make their homes in almost every habitat, including woodlands, fields, freshwater streams, marshes and human habitations. They also vary widely in size, from 0.1 to 10 inches.
Though all spiders produce silk, not all spin webs. Some run along the ground hunting their prey, whereas others hide and wait for prey to walk by. Food items on a spider's menu range from insects to frogs to birds, depending on the species. Many spiders have venom that they use to stun or kill their prey, though very species have venom that can harm humans (the black widow being one notable exception).
Many spiders mate during spring or fall. In some species, the female consumes the male after mating. Spiders lay eggs, sometimes in the hundreds. When the eggs hatch, the young spiders grow and shed their exoskeletons until they reach their adult size.