The black-legged deer ticks that transmit Lyme disease to thousands of Americans every year can survive below-freezing temperatures and go more than a year without a meal.
Want to see their superpowers evaporate? Bring on hot, dry weather.
When deer ticks are exposed for too long to the type of conditions that make for a perfect beach day, they will dessicate or dry out, says Constantin Takacs, a Northeastern assistant professor of biology who studies ticks in his lab.
He says deer ticks thrive in an environment of more than 90% relative humidity and start dying after a day or two when the humidity in the atmosphere is 85% or below.
“The drier the environment is, the faster they die,” Takacs says. The process is sped up when temperatures are high and accelerate the evaporation of moisture.
Aside from coming across an occasional dew drop, deer ticks meet most of their hydration needs through blood meals, Takacs says.
Biting and feeding on a mouse, bird, deer or human can swell their body weight 100 times, he says.
At the same time, they lose some of the water through saliva secretions and the process of breathing, Takacs says.
“Their breathing is a rudimentary form of animal breathing through tracheal tubes in their bodies. Usually that lets water out, not brings it in,” he says.
All of which is to say is that a deer tick that attempts to cross a brick pathway on a hot, dry day is a tick that may not survive for long.
To maintain their water content, deer ticks seek out moist and humid environments like the leaf litter on a forest floor or brushy shaded areas at the edges of lawns and woods.
“You have that transition space between pasture and forest. There’s trees, there’s shrubbery. All of that maintains a lot of fallen leaves and traps water. The soil is going to be humid under those rather thick layers of leaves.”
Does that mean you can forego tick protection on a hot, dry day?
No, says Takacs.
He says deer ticks could still be hanging out on grass or brush as high up as 24 inches or more, waving their forearms in a behavior called questing as they seek to grab on to the next provider of a blood meal.
To kill any hitchhikers on your clothes after you have been outdoors, throw the clothes in the dryer and turn the dial up to high heat.
The Centers for Disease Control and Prevention suggests tumbling the clothing for 10 minutes — longer if damp. If the clothes require washing first, set the water temperature on hot as cold and medium temperatures will not kill deer ticks.
In fact, a study found that a cold water wash killed zero ticks.
While the deer ticks that harbor the Borrelia burgdorferi pathogen that causes Lyme disease do not enjoy desert conditions, other ticks do, Takacs says.
“Once you start going up towards the Colorado plateau, you no longer have deer ticks,” he says. But the Rockies harbor ticks that can withstand drier conditions, such as the American dog tick and Rocky Mountain and Rocky Mountain wood tick that transmit the potentially fatal Rocky Mountain spotted fever.
“There’s a huge range of adaptations to environments,” Takacs says. “That’s why you can find ticks anywhere, from the rain forest to the desert.”