What biological class contains spiders, scorpions, ticks, and mites?

Spiders, scorpions, ticks, and mites belong to the biological class Arachnida.

Arachnida is a class within the arthropod subphylum Chelicerata. Its members typically have eight legs as adults and lack the antennae and wings characteristic of insects. The class includes spiders, scorpions, harvestmen, pseudoscorpions, camel spiders, whip spiders, ticks, and mites.

The word arachnid comes from the Greek myth of Arachne, a skilled weaver who was transformed into a spider. The name reflects the prominence of spiders in the group, but spiders are only one arachnid lineage. They belong specifically to the order Araneae, while scorpions belong to Scorpiones.

A frequent mistake is calling every small, many-legged arthropod an insect. Insects have six legs and three main body regions, whereas adult arachnids generally have eight legs and two principal body regions. Ticks and mites can look very different from spiders, yet their classification places them within Arachnida.