Ticks are arachnids of the subclass Acari. There are more than 800 species of ticks in two phyla:
- Hard ticks (Ixodidae) - includes about 650 species
- Soft ticks (Argasidae) - includes about 170 species
Ticks can survive as long as three years and can infect humans at any stage. The adult female lays eggs after a blood meal. The life cycle of most ticks then proceeds through three stages:
- Stage one is a six-legged larva that must take a blood meal to develop into the next stage or die.
- Stage two is the nymph, an eight-legged form that must also take a blood meal or die.
- Stage three is the last stage, which is the adult tick. The adult is also eight-legged and must take a blood meal to lay eggs or die.
The life cycle can take three years to complete in some species. At each blood meal, there is the opportunity to either become infected with a disease or to spread it to the animal where it is feeding.