Stressed snakes strike first: study

Snakes that are stressed may be more likely to strike during an encounter with a human, according to a new study which debunks the popular belief that the reptiles get more aggressive when handled or harassed by people.
Researchers found that cottonmouths with high baseline levels of corticosterone, a hormone that is used to estimate the amount of stress an animal experiences, were more likely to strike during an encounter with a person than were cottonmouths with lower baseline levels of corticosterone.
Surprisingly, an increase in corticosterone levels that occurred after a standardised stressful experience did not make the snakes more likely to strike.

"Most people think a snake is more likely to strike after you have handled or harassed it," said Tracy Langkilde, from Pennsylvania State University in the US.
"Our results show this is not true. We show that how stressed a snake gets when handled or harassed does not determine how likely it is to strike," said Langkilde.
Only eleven of the thirty-two snakes in the experiment struck after being held by snake tongs on their first encounter.

After a short period of stressful confinement, just seven of the snakes attempted to strike when held by tongs.
Researchers suggest that cottonmouths are not as aggressive as popular lore suggests and that the level of aggression a cottonmouth displays during an encounter may often be exaggerated.

They also suggest that protecting the habitats of snakes so they do not routinely experience high stress may be an effective way to reduce the incidence of snakebite.
If snakes are not stressed, they may be less likely to strike humans when encountered.
These results may have implications in the developing world where snakebites from all species result in 25,000 to 125,000 deaths a year and up to 400,000 amputations annually, the researchers said.
Although stress is considered an important factor affecting behaviour, the interaction between stress hormones and behaviour in wild animals is not well understood.
This motivated the researchers to design an experiment that could gain insight into how stress drives behaviour in snakes in the real world.

The researchers selected the cottonmouth snake, a venomous pit viper endemic to the southeastern US because it has a clear suite of anti-predator behaviours that are easy to measure.
Anti-predator behaviours include flashing the white lining of mouth - which gives the snake its common name - vibrating the end of its tail, flicking its tongue, hissing, fleeing the scene and striking.
The study was published in the journal General and Comparative Endocrinology.