Contrary to the popular belief, spiders are not insects. They do belong to phylum 'Arthropoda' - the same phylum to which insects and scorpions belong - but have some distinct features which set them apart. Only those Arthropods belonging to order 'Araneae' of the class 'Arachnida' are classified as spiders. Simply put, Arthropods are the members of kingdom 'Animalia' which are characterized by the presence of an exoskeleton, a segmented body and joint appendages. Alongside the typical Arthropod characteristics, the members of order Araneae, i.e. the spiders, are identified by their eight legs, ability to breathe air, and fangs in chelicerae which are modified to inject venom.