Bothrops jararaca, a deadly pit viper of Brazil, Paraguay and Argentina, is one of the most feared snakes in South America. In Brazil alone, approximately 20,000 people are envenomated each year by this snake–known informally in the region as “jararaca” or “yarara”. Without immediate and proper medical care, these bites can be fatal.
A new study published in Scientific Reports sifts through a trove of data on snakebite cases in the region to better understand the conditions under which Bothrops jararaca is most likely to strike. This, the researchers believe, can arm people with knowledge to reduce the probability of snakebite.
Here are the main takeaways from the extensive research effort, led by João Miguel Alves‑Nunes of São Paulo State University in Brazil:
- Steer clear of juvenile snakes. The researchers found that smaller Bothrops snakes were more likely to bite than larger ones. This is consistent with research on other snake species. As a general rule, baby and juvenile snakes are more defensive and their venom packs a more powerful punch due to their need to defend themselves against opportunistic predators such as birds.
- Don’t touch snakes, especially on the head. Not surprisingly, Bothrops snakes were more likely to strike when touched on the head as opposed to the body or tail. “Predation on venomous snakes is risky but more effective when the predator aims at the head or neck,” comment the authors. “Therefore, people stepping on the head or the frontal part of a small Bothrops jararaca greatly increases the snakebite risk.”
- Be extra cautious when the weather is warm. The researchers found that snakebites from Bothrops jararaca were more likely to occur at warmer temperatures. Temperature is a known factor that influences snake activity. For instance, in Central America, Bothrops asper, the dreaded fer-de-lance snake, is more likely to strike during warmer El Niño weather cycles due to increased activity patterns. However, other research suggests that some snake species are more likely to strike during colder temperatures, as the energy-expending costs of fleeing outweigh the risks of striking. Bothrops jararaca is different in this regard.
- Newborn females are especially aggressive. “Among all life stages, newborn females are the most prone to bite,” state the authors. Males, on the other hand, are more likely to bite as they grow.
- Most snake bites occur in the morning. Even though Bothrops jararaca is a nocturnal animal, the authors found that more snake bites occur during the morning hours than in the afternoon or evening. The one caveat, here, is for adult males–they are more aggressive at night than during the day.
“This study highlights that the likelihood of jararaca biting people is highly dependent on contextual factors,” say the authors. “These snakes tend to become more prone to bite during the day and in warmer temperatures. They are more likely to bite when stepped on, especially on the anterior part of the body. Young snakes, particularly young females, are more prone to biting, which explains why this size class is the major cause of snakebite.”
Interestingly, the authors reported no difference in defensive behavior between captive and wild Bothrops snakes.
“Some studies on viperids report a difference in the antipredator behavior of captive snakes compared to those in the wild,” state the authors. “However, in our study, we found that the propensity to bite and tolerance do not differ significantly between snakes in captivity and their wild counterparts.”
I am an American evolutionary biologist, based at Rutgers University, where I specialize in biodiversity, evolution, and
...