Ticks are a group of more than 800 parasitic arthropods that are closely related to mites. They feed on blood from birds, reptiles and warm-blooded mammals. The life cycle of a tick varies depending on the species and family of tick, but it generally progresses from an egg to a larvae, then to a nymph and finally to an adult.
The Argasidae family, or soft tick family, includes about 160 species. These arthropods have soft, lumpy bodies and hidden mouthparts. Ixodidae, or hard ticks, have hard, plated bodies and visible mouthparts. Researchers had recognized about 650 varieties of hard ticks as of 2011.
The life cycle of a tick begins in the egg stage. Both soft and hard ticks hatch into six-legged larvae, also called seed ticks. After molting, they mature into eight-legged nymphs, then finally transform into eight-legged adult ticks that mate, lay eggs and continue the cycle.
Ticks require a blood meal at each life stage. Larval and nymphal ticks cannot molt and transform to the next stage of their development without ingesting the nutrients that blood provides. The life cycle of a tick can take as long as three years to complete, depending on how many hosts it requires.
Some hard ticks, such as dog or cattle ticks, feed on only one species and do not change hosts. Others switch between animals as they mature. A few species have a two-host cycle, but most hard ticks have a three-host cycle.
A three-host hard tick feeds on the blood of small animals such as birds or mice while it is still in the larval stage. After molting and becoming an eight-legged nymph, it switches to a larger host, such as a rabbit. After molting a final time and maturing into an adult tick, it changes hosts a third time, this time to an even larger animal, such as a deer or cow.
The life cycle of a tick also varies depending on the number of times it molts before reaching adulthood. Some types of hard ticks molt only twice. Soft ticks might have as many as seven developmental stages, or instars, before maturing into adults.
Many ticks are not able to complete their life cycle. Some species can survive for months or even years without a blood meal, but the life cycle of a tick ultimately depends on whether the young tick can find a suitable host so that it can feed and prepare for the next instar. Most ticks die because they are unable to locate a host.