Question: Are all snakes slightly venemous?

Adam Hargreaves answered on 21 Jun 2017:

Hi sebash_05_uto,
My short answer to that is no. There’s a lot of debate as to when venom evolved in reptiles, but the results seem to point to it evolving twice, once in the venomous lizards (the Gila monster and the beaded lizard) and once in the group we call the advanced snakes which is comprised of things like cobras, vipers etc. This would mean automatically that older groups of snakes such as the boas and pythons which use constriction to kill prey, do not have venom. It does also mean that other snake species within the advanced group of snakes, such as the corn snake which are often kept as pets, (possibly) descended from a venomous ancestor. However, they no longer have a “venom delivery system” which would be things like hollow fangs and venom glands, and they don’t use venom to subdue their prey, they use constriction instead. For that reason we wouldn’t consider those snakes to be venomous, but it is likely that their ancestor was, they have just lost venomous function in favour of another method.
That’s a very good question, I did my PhD on venom evolution in snakes and believe me there is a lot of debate about it!