Ticks are not insects. They belong to the class Arachnida of the phylum Arthropoda, which includes scorpions, spiders, and mites as well as ticks. These all have four pairs of legs as adults and have no antennae. Insects belong in the class Insecta of the phylum Arthropoda. Adult insects have three pairs of legs and one pair of antennae.
Ticks are among the most efficient arthropod vectors.
They are able to cause paralysis through neurotoxic salivary secretions and can transmit viruses, rickettsiae, bacteria, and protozoa. Many species are quite resistant to environmental stresses and may live for years. They have few natural enemies and have a wide range of hosts. The females may lay great numbers of eggs. All these factors combine to give ticks great potential as disease vectors.