Timber Rattlesnakes may reduce incidence of Lyme disease in the Northeastern United States

Background/Question/Methods

The role of biodiversity in regulating Lyme disease has been much debated, with empirical data and modeling showing that the diversity of host species and their identity can increase or decrease disease prevalence. We explored the role of snakes as predators on small mammals and modeled how that might affect the incidence of Lyme disease.  We modeled timber rattlesnake (Crotalus horridus) prey consumption based on published snake gut contents for four localities in the northeastern United States.  We determined the number of infected ticks removed from each location based on reported species-specific tick burdens.  We used published energetic models and diet composition data of C. horridus to quantify annual prey consumption in adult male C. horridus diets and determined how changes in prey community composition affected the total number of ticks removed by snakes annually. In addition to quantifying the number of ticks removed from each of the four localities, we modeled tick removal from four theoretical prey communities that span the range of habitat quality in the northeastern US.

Results/Conclusions

Model results estimated 2,500–4,500 ticks were removed by foraging snakes per site annually. This varied among sites because of spatial variation in rattlesnake diet composition. Rattlesnakes removed more ticks from more diverse prey communities than from less diverse prey communities which are typical of disturbed habitats. 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. Levi et al. (2012) showed 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.  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.