I’ve spent decades working with venomous snakes, setting-up snakebite protocols in zoos, and responding to snakebite emergencies. Today, I’m sometimes criticized for my strong stand against the keeping venomous snakes in private collections. But I have learned that, even under the best of circumstances, treatment can be hampered by gaps in our knowledge. For example, we know that the chemical characteristics of venom vary over the ranges of certain species. This can affect treatment, and, as we’ll see below, may mean the difference between life and death for a victim. In fact, the venom of some Southern Pacific Rattlesnakes is so unique that it is unaffected by the antivenin currently in use! Are they the most dangerous snake in the USA?
Rattlesnake Venom and Antivenin
We’ve known for some time that the venoms of most snakes contain both haemotoxic (attacking blood vessels) and neurotoxic (attacking nerves) properties, with one or the other predominating. The venoms of several rattlesnakes have both, but the effects of most are haemotoxic in nature.
The antivenin administered to rattlesnake bite victims was formulated with that rule in mind. A single antivenin is used to treat bites from any of the 34 species native to the USA.
The Most Dangerous Snake in the USA? One Subspecies, Two Distinct Venoms
The Southern Pacific Rattlesnake (Crotalus oreganus helleri) is considered to be one of the most medically significant rattlesnakes in the USA. Researchers from the University of Queensland analyzed the venoms produced by two separate populations of this species. The populations studied are located in southern California, within a two hour’s drive from one another.
Southern Pacific Rattlesnakes living near Phelan, CA. produce fairly “typical” rattlesnake venom that attacks the blood vessels of a victim with anticoagulants and other compounds.
However, Southern Pacific Rattlesnakes living near Idyllwild, CA – 2 hours away by car – manufacture venom that could not be more different than that of their Phelan neighbors. Highly neurotoxic in action, this venom kills by paralyzing the nervous system (as is commonly seen in cobra bites).
Why Evolve Unique Venom?
Over time, certain prey animals evolve resistances to the venoms of their major snake predators. Snakes may respond with evolutionary changes of their own. Venom may eventually become “fine-tuned” to kill one or several specific prey animals.
For example, the venom of Timber Rattlesnakes (Crotalus horridus) living in New England is more effective against the most common local prey animal (gray squirrels, I believe) than against other creatures. Further south, cottontail rabbits predominate in the diet, and the venom’s chemical make-up reflects this. Timber Rattlesnakes living on St. Catherine’s Island off Georgia (formerly used by the Bronx Zoo to breed endangered species) seem to produce especially virulent venom, at least where dogs are concerned.
The Southern Pacific Rattlesnake populations mentioned above represent the greatest known venom variation within a species, and the distance involved is the shortest documented. Researchers theorize that the isolation of the Idyllwild population, which occupies mountain ridges near and over 4,000 feet above sea level, partially accounts for their unique venom.
Questions remain as to why neurotoxic venom has evolved among these snakes. One proposed explanation is found in the nature of the habitat, which is rocky and studded with caves and crevices. Rattlesnakes bite their prey and then withdraw, tracking their victims once they have expired. Perhaps the fast-acting neurotoxic venom allows snakes to more easily locate their victims. This may not be a consideration for snakes living in prairies and other open habitats.
Complications for Snakebite Victims
As mentioned earlier, the antivenin administered to rattlesnake bite victims in the USA was formulated to counteract the effects of “typical” rattlesnake venom, which is largely haemotoxic in nature. It is believed that people bitten by a Southern Pacific Rattlesnake living near Idyllwild would not be helped by this antivenin.
Certain populations of Mojave Rattlesnakes, C. scutulatus and the Neo-Tropical Rattlesnake, C. durissus, have long been known to contain neurotoxins. If I recall correctly from my days at the Bronx Zoo, bites from these species were treated with a mix of 2-3 antivenins (I’ve not checked current treatment recommendations; please post below if you need further information).
An abstract of original article (Journal of Proteomics, 24 Jan 2014) is available here.