Rattlesnake

? Rattlesnake
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Reptilia Order: Squamata Family: Viperidae Genus: Crotalus Sistrurus
Species
27 species; see list of rattlesnake species and subspecies.

Rattlesnakes are a group of venomous New World snakes, genera Crotalus and Sistrurus. There are about 30 species, with numerous subspecies. They 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.

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 sacs on either side of the back of the jaws, giving a triangular shape to the head.

Habits

Rattlesnakes feed on rodents and other small animals by striking them rather than holding them. The bite stuns most prey species immediately. The snake will follow larger animals that attempt to run away. Some rattlesnakes hibernate for the winter in northern areas and at higher altitudes. Most rattlesnakes mate in the spring and all species give live birth. Mothers care for their young for 7 to 10 days.

Safety and identification

Rattlesnakes often sun themselves on warm rocks. Different species of rattlesnake vary significantly with respect to temperament. Some are relatively docile, while some are quite aggressive when challenged. They may flee from encounters with humans but will not necessarily do so. Bites often occur when humans provoke a snake, for example by poking it with a stick. People may underestimate the range and speed with which a coiled snake can strike. Boots and long pants are recommended for hiking in rattlesnake areas. Remain observant and avoid potential encounters. Prevent pets or companions from provoking a snake.

While not all rattlesnakes have rattles, they can always be identified as poisonous by their heads. Like all pit vipers, a rattlesnake has cheeks that are wider than the rest of its body. Some observers describe this as a "diamond shaped head." In some regions such as the Western United States this feature is sufficient to determine whether a snake is poisonous. Other areas such as Florida contain poisonous snakes that are not pit vipers. So while every diamond headed snake is poisonous, some smooth headed snakes are also poisonous. Outdoor enthusiasts should memorize the characteristic markings of local species.

Rattlesnake bites

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. Although capable of delivering less venom, some studies indicate that very young snakes have venoms which are more potent on a concentration basis than their adult counterparts. This makes their bite every bit as dangerous as a bite from an adult snake. 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 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. Even adult snakes may lose their rattles on occasion as well. 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 do not give advance warning.

Venom

Most (but not all) rattlesnake venom is primarily hemotoxic, meaning it is essentially digestive, destroying tissue and is often very painful. Rattlesnakes have the most potent hemotoxic venom of any snake, making them one of the most dangerous snakes in the world. A few other snakes have stronger venom, but the large amounts of venom large rattlers can inject make their bites one of the worst. 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. Thus, a rattlesnake bite is always a potential serious or even fatal injury. The most poisonous species is the Mojave Rattler, which has a venom 75 times as potent as an Indian Cobra. The most dangerous species are the diamondbacks, which can possess enough venom to kill several hundred humans, even though their venom is considerably less potent than some species such as the Mojave or Midget Faded Rattlesnakes.

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—rattlesnake bites are generally not fatal for adult humans, if promptly and properly treated. However an untreated Rattlesnake bite very often proves fatal. Bites by neurotoxic species such as the Mojave Rattlesnake should be field treated by wrapping the bitten limb with an elastic Ace-type bandage to impede the spread of the poison for as long as possible. This is not a tourniquet, and should be wrapped only as tight as one would wrap for sprain, impeding the subcutaneous circulation through which venom travels. Tourniqueting or using a tight ligature is not recommended for any type of snakebite. Tourniquets are tight, narrow ligatures and should not be confused with wide Ace-type elastic bandaging which is useful in impeding the spread of neurotoxic venoms.

When a bite occurs, the amount of venom injected 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. Experienced health workers typically gauge envenomation in stages (0-5), from no evident venom to severe destructive amounts. The stages are equated to the amount of bruising and swelling around the fang marks and the speed with which bruising and swelling progress. In more severe envenomation cases (Stage 4 or 5) there may also be distant symptoms like lip-tingling, dizziness, bleeding, vomiting, or shock. Quick medical attention is critical, and typical treatment requires antivenin/antivenom 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.

In the United States there is a recently developed antivenom with the trade name Cro-Fab™ which is made from antibodies raised in sheep that have been inoculated with several different types of North American pit viper venoms. This new antivenom is highly purified and is much safer and more effective than the horse serum based antivenom it has essentially replaced.