Northern Viper

The northern viper, or common adder, is a short, stout venomous snake with a clear dark zigzag running down the back. Ground colour varies from grey in many males to brown or reddish in many females; entirely black individuals also occur. A dark V or X often marks the head, and the pupil is vertical. The zigzag is useful but variable, so any stocky snake should be observed without close approach. (Wikipedia, Vipera berus account)

Adders use heath, bog, meadow, forest edge and rocky openings across northern Eurasia. They bask to regulate body temperature and ambush small mammals, lizards and frogs, relying on venom before swallowing prey. Northern populations hibernate communally and emerge when spring temperatures permit. Mating follows emergence, and females give birth to live young later in the warm season. The opened account did not provide Mongolia-specific distribution or a named site, so no local encounter guidance beyond keeping distance is offered. (Wikipedia, Vipera berus account)