Spider species are distinguished and identified by "markings."
Spiders are identified by structure. They are classified into families by the arrangement of the eyes (see above), number of claws, location and arrangement of certain specialized hairs and spines (see above), structure and arrangement of the spinnerets (silk spinning organs at rear end), and other characters that you cannot see with the naked eye. Within families, species are separated mostly by the fine structure of the sex organs (yes, really, I'm not kidding! see below), which can't be seen without high magnification. Color patterns can be very variable within species, and very similar between different species. For example, the majority of all spider species can be seen as having a "violin" shape somewhere on their bodies; thousands of species have a pattern of "chevrons" on the abdomen. These and other pattern features do not indicate any particular species, and are not signs of danger to humans.