Why are ticks not classified as insects?

Ticks are not classified as insects because they belong to the class Arachnida, which distinguishes them from insects that are in the class Insecta. One of the defining characteristics of arachnids, like ticks, is that they have eight legs in their nymph and adult forms. In contrast, insects have six legs. This key difference in leg count is critical in the classification system of animals.

The presence of eight legs instead of six is fundamental in determining the group to which an organism belongs. This biological and anatomical difference is utilized by taxonomists to categorize and differentiate various arthropods, leading to the clear classification of ticks as arachnids rather than insects.