Snakes in Costa Rica Bite People More Often During El Niño Years

Snakes, like other reptiles, rely on the environment around them to regulate their body temperature, and that makes them very sensitive to temperature fluctuations like those brought by El Niño. Changes in the weather can change snakes’ activity levels, their distribution, and their foraging habits in ways that may bring snakes into contact with people.

Researcher Luis Fernando Chaves and his colleagues studied snake bite records in Costa Rica — where reporting of snake bite injuries is mandatory and encouraged by free treatment at clinics — from 2005 to 2013. They matched increases in snake bites to changes in the weather, and found that more people reported snake bites during the hot and cold phases of the El Niño Southern Oscillation, compared with normal years.

The El Niño Southern Oscillation is a multi-year cycle of changes in Pacific Ocean water temperature. During the hot phase of the cycle, known as El Niño, a blob of unusually warm water forms off the coast of Peru and Ecuador around December. It cools off during the cold phase, known as La Niña. Because Earth’s oceans play such an important role in shaping weather patterns, the oscillation causes weather fluctuations across the equatorial Pacific and much of North America.


Chaves and his colleagues say that during the hot El Niño phase, warmer temperatures make snakes more active because their usual prey is more abundant. And during the cold La Niña phase, weather changes cause prey to become scarce, driving snakes into new foraging areas. Both of those situations can bring snakes into contact with people, especially in rural, agricultural areas where human activities already encroach on snakes’ natural habitat.

As the world’s climate changes, extreme weather fluctuations are expected to become more common, so researchers say the world might see an increase in snake bites. It’s another example of how climate change causes ecological change that can directly impact humans. And since most snake bite patients live in rural areas with relatively low income, the study also underscores how the world’s poorer populations are also the most vulnerable to these changes.


You can read the study in the journal Science Advances.

Top image: Bernard Dupont via Wikimedia Commons

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