Timber Rattlesnakes Help Control the Spread of Lyme Disease

Outbreaks of Lyme disease in the eastern US are being kept in check by the timber rattlesnake but the snakes are facing their own habitat crisis as well, according to researchers at the University of Maryland.

The timber rattlesnake, a type of North American viper, has a range comprising the majority of the Eastern United States, where it makes its home in forests and feeds off of mice and other small animals.

Frequently, mice and other creatures are not alone as they scurry about the forest. They often carry black-legged ticks, which are the source of the bacterial illness known as Lyme disease. As the timber rattlers feed on their small prey, they subsequently inject the ticks being harbored by the creatures.

After analyzing timber rattlesnakes in four different forest locations around the East, Edward Kabay, a former University of Maryland graduate student, found that the snakes are responsible for consuming anywhere from 2,500 to 4,500 ticks from each site annually. The large variance was attributed to the types of prey available to the rattlesnakes. Foxes and other mammal predators help control Lyme disease by keeping small mammal populations in check.

"Rattlesnakes removed more ticks from more diverse prey communities than from less diverse prey communities which are typical of disturbed habitats," Kabay wrote in the conclusion to his research, which indicates that snakes played a large role in tick population control, but also that the decline of small mammal predators may also be a factor in Lyme disease's prevalence among humans.

Because ticks are vectors for Lyme disease in the northeastern US, snake predators may play an important role in reducing tick burden and may reduce human exposure to Lyme disease, Kabay said, noting that prior research on Lyme disease shows that "reduced abundance of mammal predators increased numbers of ticks which in turn resulted in increased incidence of Lyme disease in humans."

"Our model results suggests apex predators like many species of vipers may play important roles in regulating incidence of Lyme disease through predation on small mammals. Timber rattlesnakes populations are declining under pressure from decreasing habitat and overharvest, especially in northern and upper midwestern populations where the incidence of Lyme disease is the highest," Kabay wrote.

"Our research highlights the importance of biodiversity for human health and identifies several research areas on the effectiveness of ecological education and conservation efforts for these important predators."

Timber rattlesnakes are listed as endangered in six states and threatened in five more under the Endangered Species Act.

"Habitat loss, road kills, and people killing them out of fear are the big issues," said Karen Lips, a University of Maryland associate biology professor. "They are non-aggressive and rarely bite unless provoked or stepped upon."

The research will be presented at the Ecological Society of America's 98th annual meeting in Minneapolis.