Are Grass snakes Venomous?
No they are not. At least not in the sense that they are able to inject venom into prey.
The Duvernoy’s Gland is situated in the snakes head behind the eye and provides a similar function to that of venom glands in vipers and elapids. Colubrids, like our grass and smooth snakes aren’t venomous but the Duvernoy’s gland produces a digestive accelerant (which is essentially what snake venom is). The glands are much less developed and they don’t deliver their contents quite as efficiently as happens in true venom glands.
Grass snakes and other Colubrids lack fangs however, so the gland secretes its mild toxins, which pretty much dribble down the groove between the gums and the outer lips, onto the teeth at the rear of the snakes mouth and are then absorbed into the preys skin, where they begin to work.
True venom glands such as those possessed by our native viper the adder are powered by muscular pressure to force venom into the highly specialised syringe like, hinged front fangs. This takes the evolution to a much higher level than that of the Duvernoy’s gland.
Given time we may see grass snakes evolve to a point where they need to subdue highly evolved frogs. Maybe in a few million years I’ll be back in another plain of existence to witness it. Perhaps it’s happening now in a parallel universe where herpetologists are in parliament.