Also, even true vipers are capable of detecting heat well through nerves in the face. In other words, even though snakes are not capable of recognizing prey simply by sight alone, they use other senses to supplement vision. Well, snakes go under the frostline, of course. But this depends on the climate. It may be a matter of inches or feet, depending upon how cold it gets in their particular region.
Many snakes hibernate in burrows dug by other animals.
Some hibernate in rock crevices. Most do not dig their own burrows. The length of their fangs varies tremendously. They may be only one or two millimeters long, in the case of rear-fanged snakes. This african viper has fangs that may approach 2 inches in length.