You are in the garden. As you bend down to pick a tomato, you see a: snake! Whoa – that snake has a triangular shaped head! Is the snake venomous?
Many people mistakenly believe that all snakes with triangular shaped heads are venomous. And not just people: a recent study in Spain has even shown that predators such as hawks and eagles will often avoid snakes with triangular heads! Valkonen, J., Nokelainen, O., & Mappes, J. (2011). Antipredatory Function of Head Shape for Vipers and Their Mimics PLoS ONE, 6 (7) DOI: 10.1371/journal.pone.0022272
The fact is, however, that many harmless snakes mimic the viper-like head shape when they are frightened. Harmless snakes including garter snakes, rat snakes, and water snakes will flatten their heads and bodies when they feel threatened. And snakes in the garden feel threatened when they see people.
So is there an easy way to know if a snake is venomous or harmless? No, not really. Herpetologists and snake experts learn to identify snakes using a variety of physical characteristics. There is also individual variation within species: albinism, melanism, and pattern variations that occasionally occur can cause confusion when trying to identify a snake.
At Reptiles Alive, we suggest that people just leave all snakes alone. If you leave snakes alone, snakes will leave you alone. That way it does not matter whether the snake is venomous or not – even venomous snakes will leave you alone if you don’t bother them.