Rattlesnakes
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27, including:
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Rattlesnakes are a group of venomous New World snakes, genera Crotalus and Sistrurus, which have a small noise-making jointed rattle on their tails. If not surprised, they will usually use this rattle as a warning device when they feel threatened. The rattle is composed of a series of nested, hollow beads which are actually modified scales from the tail-tip. Each time the snake sheds its skin, a new rattle segment is added. Since they may shed their skins many times a year (depending on food supply and consequent growth rates), and since the rattle can and does break, there is no truth to the claim that one can tell a rattlesnake's age from the number of rattles. There are about 30 species, with numerous subspecies.
Rattlesnakes are pit vipers. Pit vipers have heat-sensitive pits between the eye and the nostril that enable them to find prey very effectively. The pits give information to the snake of both distance and relative size, allowing them to strike at the warmest part of the prey. Pit vipers also have fangs in the upper part of the mouth that fold in when not in use. When a pit viper attacks, it unfolds the fangs, bites, and injects its venom. The venom is held in sacks on either side of the back of the jaws, giving a triangular shape to the head.
Rattlesnake bites are generally not fatal for adult humans, if promptly and properly treated. Most (but not all) rattlesnake venom is primarily hemotoxic, meaning it is essentially digestive, destroying tissue and is often very painful. Some degree of permanent scarring is very likely, even with prompt, effective treatment, and a severe envenomation combined with delayed or ineffective treatment can lead to loss of a limb; a rattlesnake bite is always a potential serious injury.
Some rattlesnakes, especially the tropical species, have primarily neurotoxic venom. A bite from these snakes may not be very painful, but the venom can interfere with the function of the heart, and can paralyze the lungs. Prompt treatment is essential for any victim of a rattlesnake bite.
Different species of rattlesnake vary significantly with respect to temperament. Some are relatively docile, while some are quite aggressive when challenged. Rattlesnakes control the amount of venom they inject, generally delivering a full dose to prey, but less or none when biting defensively. A very significant exception to this is a badly frightened or hurt snake, or a very young snake which has not yet learned to gauge the venom delivered. For defense, it is not unusual for a snake to try to deliver smaller venom doses repeatedly. No matter the circumstance, always assume that venom has been injected and seek immediate help if bitten.
Rattlesnakes are born live and are born with fully functional fangs that deliver venom. Newborn rattlesnakes do not have functional rattles; they only have one segment with nothing for it to rattle against. In wet weather, if the rattle has absorbed sufficient water, it will not make noise - another reason not to rely on a warning from a rattlesnake. Even with a useful rattle, a rattlesnake might not always give a warning. There has been speculation that rattlesnakes that use their rattles around humans are often killed. Natural selection might favor rattlesnakes that don't give advance warning.
TimberRattler.jpg
If a bite occurs, the amount of venom injected (envenomation) cannot always be gauged easily. Symptoms and swelling may occur quickly, but in some cases there may also be hours that pass before the worst effects appear. Quick medical attention is critical, and typical treatment requires antivenin to block the tissue destruction, nerve effects, and blood clotting disorders common with rattlesnake venom. Most medical experts recommend keeping the bitten body area below the heart level, and keeping the victim calm while transporting them. It is currently not recommended for untrained people to make incisions at or around bite sites, or to use tourniquets, since the damage from this "treatment" may end up being worse than the bite itself would have caused.