Snakebites, contrary to public opinion, increase after rainy years, not drought, according to a new study that examined two decades of rattlesnake bite history in California. The study was published online this week in the journal Clinical Toxicology.
The western rattlesnake (Crotalus oreganus). Image credit: California Department of Fish and Wildlife.
Little scientific evidence links drought to an increase in snakebites, and yet everyone seems to believe there’s a connection, including emergency medicine providers, since that’s what they’re taught during training.
The prevailing theory goes that snakes wander further to forage for food during times of drought, plus they are simply more active in warmer weather.
“We set out to prove that, yes, there are more snakebites during high drought time especially since that’s what we were taught,” said study lead author Dr. Grant Lipman, an emergency medicine physician at Stanford Medicine.
“In fact, what we found was the exact opposite.”
Dr. Lipman and colleagues pored through 5,365 cases of rattlesnake bites reported to the California Poison Control System between 1997 and 2017.
Details included the date and time of the bite; the patient’s age and sex; where the bite occurred on the body; call site; treatment; and medical outcomes. The median age of the patients was 37. They were most likely to be male, and the bites most often occurred at home in the backyard.
The majority of bites occurred during the spring or summer and in counties dominated by shrub or scrub growth.
Mariposa County topped the list with the most bites at 96 bites per 1 million people. In Santa Clara County, where Stanford is located, there were 4 bites per 1 million people.
The scientists compared those cases to a range of other information, including climate data from NASA and drought records from the National Drought Mitigation Center.
What they found was surprising: when California counties experienced drought, recorded cases of snake bites dropped off.
Those incidences hit record low levels statewide in 2015 and 2016 when California was in the middle of a historic dry spell.
“The decrease isn’t huge, but it’s a significant change if you’re considering the public health implications,” said study first author Dr. Caleb Phillips, a researcher at the University of Colorado-Boulder.
“This study shows a possible unexpected, secondary result of climate change. We probably need to take climatological changes into account when we coordinate systems that may seem unrelated like planning how we distribute antivenin supplies or funding poison control centers.”
“We can predict a big snakebite season because of prior wet winters and have antivenom in places where there are a lot of hikers or trail runners,” Dr. Lipman said.
“It’s important information for people who work and play in California.”
“We urge outdoor enthusiasts to stay calm. You can avoid snakes with a simple strategy: give rattlers plenty of room and exercise common sense,” Dr. Phillips said.
“If you encounter a rattlesnake, don’t pick a fight with it, and it won’t pick a fight with you.”
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Caleb Phillips et al. Snakebites and climate change in California, 1997-2017. Clinical Toxicology, published online September 4, 2018; doi: 10.1080/15563650.2018.1508690
