The deer tick Ixodes scapularis, also called the blacklegged tick, is a type of tick native to the eastern United States. This arthropod is a major carrier of Borrelia burgdorferi, which is the bacterium that causes Lyme disease. Although deer ticks occasionally feed on human blood, humans are not a preferred part of their three-host life cycle.
A deer tick begins life as an egg and hatches into a tiny, tan larva. It feeds on the blood of small animals such as mice and other rodents. The larva ingests blood for several days before releasing its host. It needs to feed only one time while in the larval stage. After completing a blood meal, the larval tick molts into a beige nymph with a dark head.
As a nymph, a deer tick feed on larger animals such as squirrels and cats. It might also feed on human blood during this stage. Nymphs, like larvae, need to feed only once. It falls from the animal, drops to the ground and molts into an adult.
Adult male deer ticks are solid black, and the slightly larger females have red bodies and black legs. These ticks are roughly the size of a sesame seed before feeding but become larger when their bodies are engorged with blood. An adult deer tick feeds on large mammals such as deer and cattle, as well as canines and humans.
These ticks take about two years to complete all four life stages. During the spring, the female ticks disengage from their hosts. They lay about 1,000-3,000 eggs in the grass and then die.
The emerging larvae usually stay in the general area where they were hatched, where they wait for a potential host to come by. The chances of a larval deer tick finding a blood meal are slim. Many die of starvation, disease or predators before reaching adulthood.
Larval ticks ingest the Lyme disease bacterium from animals such as white-footed mice. They carry these spirochetes in their bodies throughout their life stages and pass the disease to future hosts. They are most likely to pass the disease to humans when they are in the nymphal stage.
Humans who are infected with the disease experience joint pain and swelling, headache, fever and a ringed rash at the site of the tick bite. Untreated infections can lead to heart problems, vision disorders or arthritis. Lyme disease usually can be treated successfully with antibiotics if it is caught in the early stages.