You can always tell a spider because it has eight legs. Fact: Not exactly. Scorpions, harvestmen, ticks, and in fact all arachnids—not just spiders—have four pairs of legs (see illustrations). Insects have three pairs.
Generally, most spider have eight (8) legs, which are arranged in pairs. They have four pairs of legs. The arrangements of their legs helps in their fast mobility.
In general, spiders typically possess eight legs, which are organized into pairs. With four pairs of legs, spiders utilize this arrangement to facilitate their rapid mobility.