Why are mites and ticks the closest relatives of the spider?

Mites and ticks are the closest relatives of the spider because they share a common ancestor and are found on the same clade.

Mites and ticks are the closest relatives of the spider because they all belong to the family of A rachnids or joint-legged animals (eight legs), spiders being the largest order in the class. Mites and ticks also belong to this class. The three are closest relatives since, unlike other insects which belong to the same class, they all breathe using spiracles.