Los Angeles County West Vector & Vector-Borne Disease Control District

What is a Tick?

   Ticks belong to the class Arachnida, which includes spiders, scorpions, and mites.  Ticks go through four life stages: egg, larvae, nymph, and adult.  The larvae have six legs while the nymphs and the adults have eight.  Ticks are divided into two families, "soft" ticks and "hard" ticks.  The only source of nutrition that ticks use is the blood sucked from their hosts.

    In the United States, seven kinds of hard ticks and five kinds of soft ticks carry diseases, are a nuisance, or cause paralysis.  Often these diseases are transmitted by the ticks saliva during feeding behavior.  However, some diseases, such as tularemia, can enter through the skin if a person comes into contact with a crushed infected tick.  In recent years, Lyme disease has become the most reported arthropod borne disease in the country.  Many experts feel that if it were not for AIDS, Lyme disease would be the number one infectious disease in the United States.

    The front part of a tick consists of the "head" area and the mouthparts (see photo, left).  The mouthparts have a central structure, the hypostome, which is shaped like a blunt harpoon, flat on the top and curved on the bottom where many sharp barbs are located.  

    A tick pushes its hypostome into a hole in the skin of a host that has been made by sharp teeth in the front of the hypostome.  The barbs anchor the tick to the skin and make it difficult to pull the tick out (see right).  Some ticks also produce a cement-like substance that helps anchor them to the host.  Sharp teeth at the front of the hypostome cut blood vessels under the skin, causing the blood to form a pool.  The tick then sucks this blood into its gut through the hypostome.  To keep the blood from clotting, ticks inject saliva containing a kind of anticoagulant into the blood pool.  The saliva may also contain disease organisms, such as Borrelia burgdorferi which cause Lyme disease.

      Ticks are found wherever their hosts are found.  Some ticks feed on only one type of host, while others suck blood from many different animals.  When not attached and feeding on their hosts, most hard ticks live on the ground in vegetation, such as grassy meadows, woods, brush, weeds, leaf litter, etc.  Most ticks will crawl to the tips of grasses, brush, leaves, or branches and wait.  With their front legs outstretched, they will wait for a host to brush up against them. This behavior is called questing (see photo left). When the tick does come into contact with an animal, it will grab on and crawl to an appropriate area on the animal to feed.  

    The two most common ticks found outdoors in west Los Angeles County are the Western Black-Legged Tick (Ixodes pacificus) and the Pacific Coast Tick (Dermacentor occidentalis).  The Western Black-Legged Tick is the vector of Lyme Disease in the western United States, while the Pacific Coast Tick carries Tularemia and is a suspected carrier of Rocky Mountain Spotted Fever and Colorado Tick Fever.  The Brown Dog Tick (Rhipicephalus sanguineus) has evolved to live indoors and can be found living inside your home.  Brown Dog Ticks do not usually feed on humans.