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Ticks Overview and Life Cycle

Ticks are small bloodsucking arthropods and are composed of two families, Ixodidae (hard ticks) and Argasidae (soft ticks); each contain different genera and species of ticks.

Ticks are the leading carriers (vectors) of diseases to humans in the United States, second only to mosquitoes worldwide. In most circumstances, it is not the tick bite but the toxins, secretions, or organisms in the tick's saliva transmitted through the bite that cause disease.

Ticks (and mites) are arthropods, like spiders. There are more than 800 species of ticks throughout the world. Many organisms that bite humans for a blood meal are not ticks and should not be confused with ticks. Some common examples are mosquitoes, bedbugs and fleas (these are insects, not arthropods). If it is possible to bring into the doctor's office what has caused a "bite," the physician may be able to determine what potential vector caused the "bite."

Two families of ticks, Ixodidae (hard ticks) and Argasidae (soft ticks), are important to humans because of the diseases or illnesses they can transmit or cause. Hard ticks have a tough back plate or scutum that defines their appearance. The hard ticks tend to attach and feed for hours to days. Disease transmission usually occurs near the end of a meal, as the tick becomes full of blood. Figure 1 shows several hard ticks and the various stages in their life cycle. The stages are part of the life cycle of ticks; the smallest stages, larva and nymph, are sometimes generally referred to as "seed ticks" because they resemble small plant seeds.

The life cycle of ticks.

Figure 1: The life cycle of ticks. Source: CDC

Soft ticks have more rounded bodies and do not have the hard scutum found in hard ticks. These ticks usually feed for less than one hour. Disease transmission from these ticks can occur in less than a minute. The bite of some of these ticks produces intensely painful reactions. Ticks can transmit disease to many hosts; some diseases cause economic harm such as Texas fever (bovine babesiosis) in cattle that can kill up to 90% of yearling cows. Figure 2 shows the body of a soft tick; there is no hard scutum, only the soft body. The adult soft ticks are about the same size as adult hard ticks (see Figures 1 and 2).

Picture of a soft tick.
Figure 2: Picture of a soft tick. Source: CDC

Medically Reviewed by a Doctor on 8/6/2015

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Patient Comments & Reviews

The eMedicineHealth doctors ask about Ticks:

Ticks - Experience

What was your experience with ticks?

Ticks - Preventive

How do you prevent ticks from getting on your dog?

Learn how to reduce your risk of exposure to ticks.

Where Ticks Come From

Medical Authors: Barbara K. Hecht, PhD, Frederick Hecht, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

Ticks carry the bacteria that cause Lyme disease. People contract Lyme disease by being bitten by these ticks.

In order to investigate whether specific human behavior increases the risk of tick exposure, researchers from the University of California at Berkeley took to the woods. They found that sitting on a log carried with it the greatest risk of picking up a tick. If you sit on a log (at least in Northern California) for only five minutes, you have a 30% chance of getting a tick on you! Gathering wood was also cited as a risky activity as well as leaning up against a tree.

Comment: Aside from issuing a press release (below) about this study, it was also published in the current issue of the Journal of Medical Entomology. In case you aren't familiar with this journal, it is chock-full of everything you might want to know (or not know) about the dangers that mosquitoes, cat fleas, ticks, flies, scorpions, mange mites and other insects pose to you. We don't recommend it for bedtime reading.

Read What Your Physician is Reading on Medscape

Tick-Borne Diseases, Introduction »

Ticks are excellent vectors for disease transmission.

Read More on Medscape Reference »

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