Scientists believe there may be up to 50,000 to 100,000 kinds. Some are smaller than than the head of a pin but some are larger than a person's hand. One kind of spider, a South American tarantula is measured at 25 centimetres but that is with its legs extended. Most people think spiders are insects but scientists classify spiders as arachinids. Insects are different in a number of ways.
Spiders have eight legs but ants, bees, beetles and other insects have only six legs.
Most insects have wings or antennae which are feelers. Arachinids include daddy long legs, scorpions, mites and ticks. Scientists classify spiders as either true spiders or Tarantulas, according to certain differences in their bodies such as the way their fangs point and move. In addition, spiders can be grouped according to the way they live. Web spinning spiders spin webs to catch insects.