Fear or fascination – encounters with rattlesnakes (Crotalus sp. & Sistrurus sp.) are always exciting experiences for the people of northern and central America. Because of their signature feature, their rattle at the end of their tails, they are probably amongst the easiest to identify genus of snakes in the world. And if there is anything that everybody around the world knows about these species, it is that they are all venomous!
Rattlesnakes belong to the taxonomic family of the Vipers (Viperidae) and belong to the subfamily of Pit Vipers (Crotalinae). They represent the classic image of a Viper, including their long, needle-like fangs folded back into their mouths that deliver the venom to the prey in case of a bite. Most species of Pit Vipers, including rattlesnakes, are highly venomous and carry a mix of toxins that attack the victims blood clotting factors and connective tissues. Unlike the Old World Vipers (Viperinae), the Crotalinae posess an extra organ, the heat pits lying between their eyes and nasal pits, which they use to detect heat waves from their surroundings. This helps them spot their prey by detecting slight differences between the prey animals body heat and the cooler environment, which is especially useful in the dark.
Pit Vipers usually have a large, triangular head covered in irregularly distributed small scales. However, some genera have rather large and symmetrical scales on their forehead. The pupils of Pit Vipers are usually elliptical and are narrowed down to two vertical slashes when exposed to bright daylight. The subfamily of the Crotalinae is distributed all over Asia and the New World, but the highly specialized genus of the rattlesnakes is only found throughout America. If you are interested in learning more about Pit Vipers in general, click HERE.
Rattlesnakes get their name from their signature rattle, which is made out of loose, connected and hollow scale structures. If the snake shakes its tale rapidly, the scales vibrate and create the rattling sound so many people fear. At birth, a rattlesnake posesses only one individual modified scale at the end of its tale. Everytime the snake sheds its skin, one segment is added to the end of their tale, creating a growing rattle as the snake ages. Sometimes however, the segments can break off during the snakes live, so the length of a snakes rattle is not a sure indicator of its age. This feature has evolved as an advanced warning system for the snake. When confronted, the snake creates a loud and intimidating noise that scares away a potential threat. All venomous snakes are very reluctant to waste their precious and energy consuming venom on an intruder, which is why they want to avoid a bite at all cost.
Most rattlesnakes belong to the genus Crotalus – the was originally adapted from the Greece word for “rattle”. This genus includes about 27 species and several more subspecies, some of which inhabit a large region and are very popular whilst others are restricted to very remote locations. However, three species of rattlesnakes belong to a different genus – the dwarf rattlesnakes Sistrurus. They differ slightly from the original genus in terms of size and scalation. Only one very special species does not have a rattle at the end of its tail – the Santa-Catalina rattlesnake Crotalus catalinensis is restricted to the remote island Santa Catalina in the gulf of California and does permanently only have one rattle segment.
Size and Coloration
Depending on the species, the Crotalus sp. vary largely in terms of size, but are generally massive and very strong for their length so that even smaller species are very impressive snakes. The largest species, the Eastern Diamondback C. adamanteus can grow up to 2.20 m long and weight up to 4 kg. Most species stay in the 60 – 125 cm range and the smallest reach only about 30 – 50 cm in length. The coloration may always be cryptic but varies to a great extent even between members of the same species. Diamondbacks get their name from their prominent diamond-like pattern and the western C. atrox can be recognized quickly by their unmistakable black and white banding across the end of their tail. Other rattlesnakes, like the black-tailed rattlesnake C. molossus have, like their name suggests, a black tail. The tiger rattlesnake C. tigris has unusual cross bands on its back and a close relative, C. pricei has a row of paired spots along its spine. Abnormal coloration, like albinos or melanistic specimens are also known and sometimes even bred in captivity.
Distribution, Habitat and Behaviour
When you think of rattlesnakes, the hot deserts of south-western USA and central Mexico come to mind. And you can indeed find the majority of Crotalus sp. in these habitats, so in deserts, dry and rocky canyons and bush land. The sidewinder rattlesnake C. cerastes for example is a true inhabitant of the desert and has developed special features for the life on hot sand. But rattlesnakes can be observed in a much greater range of geographical habitats than just the desert. The pacific rattlesnake, C. oreganus, can be found as far north as the south-western borders of Canada and also inhabits a large part of the US. Another great example is th species C. viridis, which inhabits the great plains from southern Canada to northern Mexico. C. horridus can be observed in the large territories of the eastern part of the US where the species inhabits the wast forests. Some rattlesnake species are even exclusively found in moist, foresty mountain regions and the eastern Diamondback usually found in very densly vegetated and moist habitats.
All rattlesnakes are ground dwelling snakes, but some have impressive climbing skills. They generally avoid extreme temperatures and are, during very hot days, usually spotted at night oder dawn when they leave their hiding spots to look for prey. Some species, like C. horridus, inhabiting very cold regions frequently hiberante dents, sometimes in groups of more than a dozen snakes. In most habitats, mating season starts in spring, shortly after hibernation. This can include fights amongs males for female companionship and mating usually lasts for a few hours. Like most Pit Vipers, rattle snakes are ovoviparous and have up to 20 live young. Rattlesnakes mostly have a very timid character and avoid confrontation at all cost, warning potential intruders off with their rattle. Most accidents that occur in the US are because very ignorant people were trying to catch or kill the snakes.
The prey animals of larger rattlesnake species usually includes, birds, mammals and some species of lizards. Rattlesnakes are ambush predators, so they will often sit in the same spot for days, waiting for their prey to pass. These spots are usually selected because of scent trails from prey animals and when the opportunity arrives, the snake will strike within a slit-second and envenomate the victim before releasing it again. The snake then follows the scared and dying animal and, once the venom has completed its job, consumes it head-first. Despite their potent venom, many smaller specimens and species of rattlesnakes are often preyed upon by predatory birds, badgers, opossums or sometimes even other snakes. Kingsnakes of the genus Lampropeltis seem to have specialized in hunting and overpowering other snakes, including rattlesnakes.
Unfortunately and on top of habitat loss, humans often kill every rattlesnake they come across out of ignorance. Every year, hundreds of Americans participate in rattlesnake-roundups, where the snakes fresh out of hibernation are killed in an extremely cruel and inhumane manner. According to the Humane Society of the United States, this is one of the most cruel public events in the US. It is the result of shier ignorance and cruelty towards these highly misunderstood animals. Rattlesnakes are a highly valuable part of the ecosystem and should be respected as such just like and other animal on this planet!
Venom composition and snakebites
In the event of a bite, the venom produced in a modified salivary gland at the side of the snakes head is squeezed through the hollow fangs of the snake. Rattlesnakes are solenoglyphous, so their fangs are folded back into their mouths in a resting position and can be extended when the snake opens its jaws to deliver a bite. The venom of rattle snakes is to a large part heamotoxic and hemorrhagic. This means that the peptide components of the venom attack blood clotting mechanisms or red blood cells and cause persistent bleeding or clotted up veins and arteries, along with large hemorrhages. This is usually accompanied by a drop or steep rise in blood pressure and eventual cardiac arrest in the victims body. The one exception is the species Crotalus scutulatus & Crotalus durissus with its strong neurotoxic components that attack the victims nervous system.
As mentioned earlier, rattlesnakes are very reluctant to waste their precious venom. Restoring the venom yield costs the snake a lot of energy and it has to raise its metabolism by up to 30% for a few days. Therefore, it is no surprise that these snakes are not very aggressive or defensive. Nevertheless, humans seem to get constantly wrapped up in conflicts with these animals and deaths by rattlesnake bite are not uncommon in central and southern America. On the other hand, their venom is full of potential medications and drugs that could save hundreds of lives in the future. A lot of research is going on constantly around venom compositions and the functions of individual proteins to help develop our understanding and potential use of these fascinating substances.
Rattlesnakes and traditions
Rattlesnakes have always had an important role in American history and traditional religion and medicine. For example, the god Quetzalcoatl from the Aztec empire was a rattlesnake with feathers. The Hopi in norther Arizona carry live rattlesnakes during their religious marches and pray for rain and healthy crops. Before and during the American revolution, rattlesnakes were a symbol of the American spirit. The slogan “Don’t step on me!” was used accompanied by an image of a rattlesnake to symbolize that the snake only strikes when provoked.
Actually, it was Benjamin Franklin himself who wrote about the rattlesnake as a noble creature and a symbol of America:
“I recollected that her eye excelled in brightness, that of any other animal, and that she has no eye-lids. She may therefore be esteemed an emblem of vigilance. She never begins an attack, nor, when once engaged, ever surrenders: She is therefore an emblem of magnanimity and true courage. As if anxious to prevent all pretensions of quarreling with her, the weapons with which nature has furnished her, she conceals in the roof of her mouth, so that, to those who are unacquainted with her, she appears to be a most defenseless animal; and even when those weapons are shown and extended for her defense, they appear weak and contemptible; but their wounds however small, are decisive and fatal. Conscious of this, she never wounds ’till she has generously given notice, even to her enemy, and cautioned him against the danger of treading on her.”
I hope that you enjoyed this post and that you have learned a little more about these misunderstood animals today!
If you are interested in my Sources, click HERE.
If you want to learn more about Pit Vipers, click HERE.
And if you want to study venomous snakes yourself, check out my post on great literature HERE