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| Crotalus cerastes |
Rattlesnakes are predators who live in a wide array of habitats, hunting small animals such as birds and rodents. They kill their prey with a venomous bite, rather than by constricting. All rattlesnakes possess a set of fangs with which they inject large quantities of hemotoxic venom. The venom travels through the bloodstream, destroying tissue and causing swelling, internal bleeding, and intense pain. Some species, such as the Mojave Rattlesnake, additionally possess a neurotoxic component in their venom that causes paralysis and other nervous symptoms.
The threat of envenomation, advertised with the shaking of the rattle, deters many predators. However, rattlesnakes fall prey to hawks, weasels, king snakes, and a variety of other species. Rattlesnakes are heavily preyed upon as neonates, while they are still weak and mentally immature. Very large numbers of rattlesnakes are killed by humans. Rattlesnake populations in many areas are severely threatened by habitat destruction, poaching, and extermination campaigns.
Rattlesnake bites are the leading cause of snakebite injuries in North America, and cause approximately 82% of fatalities. However, rattlesnakes rarely bite unless provoked or threatened; and if treated promptly, the bites are rarely fatal.
Range and habitat
Rattlesnakes are native to the Americas, living in diverse habitats from Southwestern Canada to Central Argentina. The large majority of species live in the American Southwest and Mexico. Four species may be found east of the Mississippi river, and two in South America. In the United States, the state with the most forms of rattlesnakes is Arizona, with seventeen species and subspecies.[5][6]
Rattlesnakes are found in almost every type of habitat that is capable of supporting terrestrial ectothermic vertebrates; but individual species can have extremely specific habitat requirements, only able to live within certain plant associations in a narrow range of altitudes. Most species live near open, rocky areas. Rocks offer them cover from predators, plentiful prey (e.g. rodents, lizard, insects, etc. that live amidst the rocks), and open basking areas. However, rattlesnakes can also be found in a wide variety of other habitats including prairies, marshes, deserts, and forests.[7] Rattlesnakes prefer a temperature range between 80 and 90°F (26-32°C), but can survive temperatures below freezing, recovering from brief exposure to temperatures as low as 4°F, and surviving for several days in temperatures as low as 37°F.[8]
Prey
Rattlesnakes consume mice, rats, small birds and other small animals[9], playing an important ecological role by limiting the size of rodent populations, which prevents crop damage and stabilizes ecosystems.[10]
Rattlesnakes lie in wait for their prey, or hunt for it in holes.[11] The prey are killed quickly with a venomous bite as opposed to constricting. If the bitten prey moves away before dying, the rattlesnake can follow it by its scent.[12][13] When it locates the fallen prey, it checks for signs of life by prodding with its snout, flicking its tongue, and using its sense of smell. Once the prey has become incapacitated, the rattlesnake locates its head by odors emitted from the mouth. The prey is then ingested head-first, which allows wings and limbs to fold at the joints in a manner which minimizes the girth of the meal.[14] The gastric fluids of rattlesnakes are extremely powerful, allowing for the digestion of bone as well as flesh. Optimal digestion occurs when the snake maintains a body temperature of between 80 and 85°F (25-29°C). If the prey is small, the rattlesnake will often continue hunting. If it was an adequate meal, the snake will find a warm, safe location in which to coil up and rest until the prey is digested.[15]
Rattlesnakes are believed to require at least their own body weight in water annually in order to remain hydrated. The method in which they drink depends on the water source. In larger bodies of water (streams, ponds, etc.) they will submerge their head and ingest water by opening and closing their jaw, which sucks in water. If drinking dew, or drinking from small puddles, they will sip the liquid either by capillary action or by flattening and flooding the lower jaw.
Venom
Most species of rattlesnakes have hemotoxic venom, destroying tissue, causing necrosis and coagulopathy (disrupted blood clotting).[30] In the U.S., some varieties of the Mojave rattlesnake (C. scutulatus) have a presynaptic neurotoxic venom component known as Mojave Type A toxin, which can cause severe paralysis.[30][31][32] C. scutulatus is widely regarded as producing one of the most toxic snake venoms in the Americas, based on LD50 studies in laboratory mice.[33]
Rattlesnake venom is a mixture of 5-15 enyzmes, various metal ions, biogenic amines, lipids, free amino acids, proteins, and polypeptides. It contains components designed to immobilize and disable the prey, as well as digestive enzymes which break down tissue to prepare for later ingestion.[25][29] The venom is very stable, and retains its toxicity for many years in storage.[25]
Older snakes possess more potent venom, and larger snakes are frequently capable of storing larger volumes of it.
Antivenom
Crotaline antivenom (or "antivenin") is commonly used to treat the effects of local and systemic pit viper envenomations.[72] The first step in the production of crotaline antivenom is collecting ("milking") the venom of a live rattlesnake - usually from the Western Diamondback (Crotalus atrox), Eastern Diamondback (Crotalus adamanteus), South American rattlesnake (Crotalus durissis terrificus), or fer-de-lance (Bothrops atrox). The extracted venom is then diluted and injected into horses, goats, or sheep, whose immune systems produce antibodies that protect from the toxic effects of the venom. These antibodies accumulate in the blood, which is then extracted and centrifuged to separate the red blood cells. The resulting serum is purified into a lyophilized powder, which is packaged for distribution and later use by human patients.[73][74]
Because antivenom is derived from horse animal, people generally display an allergic response during infusion, known as serum sickness.
Safety and first aid:-
Rattlesnakes are the leading cause of snakebite injuries in North America, and are a significant cause in Central and South America.
Avoiding bites:-
Rattlesnakes tend to avoid wide open spaces where they cannot hide from predators, and will generally avoid humans if they are aware of their approach.[60] Rattlesnakes rarely bite unless they feel threatened or provoked. A large majority of victims (~ 72%[61]) are males, often young and intoxicated. Approximately half of bites occur in cases where the victim saw the snake, yet made no effort to move away.[25]
Hikers and campers should avoid contact with rattlesnakes by remaining observant and not approaching the animals. Hikers are advised to be particularly careful when negotiating fallen logs or boulders and when near rocky outcroppings and ledges where rattlesnakes may be hiding or sunning themselves. However, snakes will occasionally sun themselves in the middle of a trail, so such areas are not the only places where they are encountered. When encountering a rattlesnake on a trail, hikers are advised to keep their distance and allow the snake room to retreat.[citation needed]
Caution is advised even when snakes are believed to be dead; rattlesnake heads can see, flick the tongue, and inflict poisonous bites for up to an hour after being severed from the body.
Effect of bites on humans
Rattlesnake bite injury:-
Rattlesnake bites are rarely fatal to humans, if treated promptly.[30] Between 7,000 and 8,000 people are estimated to have been bitten by venomous snakes in the United States each year, and about five of those die.[64] The most important factor in determining survival following a severe envenomation is the amount of time elapsed between the bite and treatment. Most deaths occur between 6 and 48 hours after the bite. However, if antivenom treatment is given within 1–2 hours of the bite, the probability of recovery is greater than 99%.[65]
When a bite occurs, the amount of venom injected is under voluntary control by the snake. The amount released is dependent on a variety of factors including the condition of the snake (e.g. having long, healthy fangs and a full venom sack) and its temperament (an angry, hungry snake that has just been stepped on vs. a satiated snake that was merely surprised by walking near it).[66] Approximately 20% of bites result in no envenomation at all. A lack of burning pain and edema 1 cm away from the fang marks after 1 hour, suggests that either no or minimal envenomation occurred. A lack of edema or erythema in the area of the bite after 6–8 hours indicates a lack of envenomation for most rattlesnake bites.[67]
Common symptoms include swelling, severe pain, weakness, anxiety, nausea and vomiting, hemorrhaging, perspiration, and heart failure.[66][68] Local pain following envenomation is often intense, increasing with the ensuing edema.[66] In general, children experience more severe symptoms because they receive a larger amount of venom per kilogram of body mass.
Emergency response:-
Data on the effectiveness of first aid techniques for rattlesnake bites is limited.[69] However, general recommendations for first aid in the field are as follows:
Remain calm, and retreat from the snake at least 10–15 feet. Arrange to have the victim transported to a medical facility as soon as possible.[69]
Remove restrictive clothing items (rings, bracelets, watches, buttoned shirts, etc.) from the victim.[69][70]
Splint or otherwise immobilize any bitten limbs, and keep them below heart level.[30][34][69][71] If (and only if) the victim is more than 1–2 hours away from a medical facility, it is recommended to place a lightly constricting band (that admits one finger beneath it) above the bitten area to prevent the systemic spread of the venom.[69]
Keep victims calm; put them at rest; keep them warm and give them comfort and reassurance (which will lower their heart rate, slowing the spread of the venom). However, keeping a victim's heart rate down should never interfere with getting him or her to a medical facility.[69]
In no case should tourniquets be used, nor should any incisions or suction be applied to the wound
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