Species On The Move

As climate change impacts habitats around the world, species are on the move, trying to adapt — and survive.

About This Species

Blacklegged ticks—also called deer ticks—only grow to the size of a sesame seed, yet they are a creature to be feared over an ever-increasing swath of North America. That is because the ticks are the primary, and perhaps only, carrier of Lyme disease, an infection that causes fever, headache, fatigue and rash. If left untreated, Lyme can spread to joints, the heart and the nervous system, according to the CDC. The ticks feed on blood and have a two-year life cycle that is strongly linked to temperature. The ticks are most active when temperatures are above 45°F and prefer areas with at least 85 percent humidity. In late May, adult female ticks lay a single egg mass consisting of up to 2,000 eggs.

Blacklegged ticks are on the rise

As blacklegged ticks expand their range, Lyme disease is on the rise. (Courtesy: CDC)

Blacklegged ticks' favorite source of blood is white tailed deer (thus the name deer tick). As deer populations have exploded in recent decades, so have ticks. Ticks spend most of their lives on the forest floor. They attach themselves to mammals—including people—as they come into contact with them. Ticks generally have to be attached for 36-48 hours to transmit Lyme disease, but they are small and often land in hard-to-see areas like the groin, armpits or scalp. They're easy to overlook.


Lyme disease was first diagnosed in Lyme, Conn. in the 1970s. It wasn't until the early 1980s that medical research connected Lyme and tick bites. As blacklegged ticks spread in the decades that followed, so did the disease. According the CDC, it is now the fifth-most reported disease nationally.

A recent study in the Journal of Medical Entomology found that there has been a 44.7 percent increase in counties recording the presence of the ticks since 1998. And they're spreading beyond the United States, too. As temperatures rise, blacklegged ticks have been increasingly showing up in Canada. In 2015, there were more than 700 reported cases of Lyme disease in Canada, up from 140 in 2009.

The Blacklegged Tick's Range

Blacklegged Ticks are associated with the northeastern U.S., but their range is expanding across the central and eastern parts of the country. Western blacklegged ticks—which also carry Lyme disease—are found on the other side of the Rocky Mountains. Both are experiencing a boom.

The Deer Tick's expanding range

Blacklegged ticks lifecycle

Blacklegged ticks—small, but mighty. (Courtesy: California Dept. of Public Health)

Looking Forward

Because blacklegged ticks prefer warmer temperatures, they are expected to spread further and multiply as the climate warms. As winter becomes shorter, there will be longer periods during which humans can be exposed to Lyme disease, and the CDC and EPA project that Lyme cases will continue to rise. 

Source: EPA, CDC

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