Snakes survive by hunting for prey, either by biting and injection of venom or through the process of constriction, and by mating to propagate their species. Many species of snake in areas where temperatures get especially low during the winter seek shelter and warmth by massing in caves to sleep together, while snakes all around the world regulate their temperatures by basking in sunlight and cooling off in shade.
Some snakes kill prey by biting it and injecting venom through their fangs. Snake venom varies in potency and may kill prey outright or simply stun or paralyze it so that the snake can feed without interruption.
Other snakes constrict their prey, wrapping it in their coils and squeezing the life out of it before swallowing it whole. These snakes tend to be larger than venomous snakes, or vipers, which rely on their venom instead of their size or strength when hunting and bringing down prey.
Snakes must work constantly to regulate their body temperatures because, as reptiles, external factors strongly impact them. They require regular access to sun and heat as well as to shade and cool in order to maintain the delicate balance that keeps them alive and active through the course of a day.