Gunalen's pit viper (Trimeresurus gunaleni). The snake was told apart from similar snake called Sumatran pit viper (Trimeresurus sumatranus) that dwells in forests up to 900 m. above see level, whereas this picture has been taken in mountains over 1700 m. It is endemic to the North Sumatra. All vipers are venomous. We can recognize them by narrow vertical pupils, their head is slightly triangular and often their tail has vivid distinctive colours.