Not only are these snakes venomous they also have a heat sensing system which helps them find prey in the dark, which is when most snakes hunt. Known as "pit vipers", these snakes have a special organ in between their eyes and nostrils. Most pit vipers hunt at night when the air is cooler, and the heat from prey is readily detected.
Most pit vipers hunt from ambush. They bite, poison the prey and then release it. Then, they will follow the dying animal, until the prey stops moving, and the snake can swallow it.
There are some advantages to the ambush style of hunting. First, it requires little energy as opposed to seeking prey. Second, the hunter is sequestered, reducing exposure to other predators which might hunt it. Third, biting and then releasing reduces the potential for injury from struggling prey.
This hunting style is supported by powerful venoms which will immobilize the prey.
