Although the bite of a copperhead is painful, it is rarely lethal. Copperheads' dens are usually among rocks, where they hibernate from late October until April. In summer they may migrate as far as 0.4 mile to lower elevations. Copperheads kill their prey by injecting them with venom through their fangs that rotate about 90 degrees from the roof of their mouth. Copperheads shed these hypodermic injectors about once a month. Several new fangs are lined up behind the functioning ones as replacements. Their venom is about six times weaker than a rattlesnake's, but copperheads bite more people.