Pit Vipers are amongst the greatest and most evolved predators on earth with highly specialized and precise methods to detect, catch and kill their prey. But they are also very shy, small and peaceful creatures.
Just like the Old World Vipers, they are extremely misjudged and mystical animals. The family of the Pit Vipers, the Crotalinae, are part of the Viperidae complex, which means that they are actually also vipers. Rattlesnakes, which do also belong to the Pit Vipers, play a great role in American culture and traditions.
In the following article, I will introduce you to these great, highly efficient and often misunderstood predators, exploring their behaviour, venom apparatus, venom composition and heat sensing heat pits.
Classification and basic Information
Vipers are separated into 4 main subfamilies, the Viperinae, Crotalinae, Causinae, and Azemiopinae. This page will focus only on the subfamily Crotalinae. The other subfamilies will be introduced separately. The Crotalinae include 151 species distributed across 18 Genera.
Just like the Vipers, Pit vipers are usually rather short and strong, except for the genus Lachesis. Also, many Pit Vipers, like the Trimeresurus, Tropidalaemus, Bothrops Agkistrodon and Deinagkistrodon often have really pointy and triangular heads, which explains their common Name – Lancehead Vipers. All Pit Vipers can easily be recognized by their most obvious trait – the large heat pits right underneath their nasal pits.
Like most other Vipers, the Pit Vipers are mostly ambush predator, which means that they can sit in the same spot for many days and wait their prey to pass by.
Snakes mostly rely on their sense of smell to detect their prey. By regularly tasting the air with their tongue, they will recognize prey approaching even at night. Then, they will strike at an incredible speed and usually hold their prey in their jaws until it succumbs.
Pit Vipers have one even more efficient way of detecting their prey – the heat pits enable these incredible predators to visualize up to 0.003° Celsius of temperature changes around them. With all these incredible detecting organs and their specialized fangs and venom delivery system, Pit Vipers are the ultimate predators. All Vipers can strike at an incredible speed and will can bite, inject venom and release their prey in less than a second.
Pit Vipers are seldom seen actively hunting or searching for prey. If a Viper is seen on the move, it may be changing its spot, basking for some energy in the sun, or on the lookout for a mate during mating season. However, many Pit Viper species are mainly arboreal and can be seen resting or climbing on branches during the night.
Generally, a viper will flee if it notices a threat, such as humans approaching. However, if confronted it will hiss very loudly, puff its body up to look bigger and strike if the treat does not back off. Some Vipers have such good camouflage that they will trust it to conceal them completely and not move at all. Other, like the Rattlesnakes, have developed sophisticated mechanisms to warn potential predators. Most accidents happen because people step on the snake they did not even see and get bit, which is neither the snakes, nor the humans fault.
Heat Pits – the most sophisticated method to detect prey
Probably the most distinct and fascinating feature of the Pit Viper is their heat sensing organ located right underneath the nostrils. These small holes enable the snake to spot their prey with infrared sensing. But new research has shown that this organ is not only used for predatory purpose, but also useful in thermoregulation and defense. It has been shown that a blindfolded rattlesnake is able to accurately strike both prey and attacker from up to a meter away and that the snake uses this special organ also to find spots to thermoregulate.
The Heat Pit consist of a deep pocket in the rostrum of the snake with a membrane stretched across it. Behind and in front of this membrane lies an air chamber, that both provides the thermosensitive nerve cells inside the membrane with oxygen, and rapidly cools it after being heated by heat radiation from a stimulus. As seen in the image, this entire mechanism is protected by another membrane at the lip of the pocket.
All Viperidae possess the most advanced fang and venom delivery system of all snake species, so-called solenoglyphous fangs. As seen in the image, a Viper can fold their massive fangs back into their mouth. When they strike, they will open their mouth up to 160° wide and unfold their fangs. Like a needle, the fangs are hollow and directly connected to the venom gland to inject their prey with venom. This entire process goes down in less than a second. Sometimes, the animal may even realize that it has been injected with venom until it dies.
Vipers regularly shed and replace their teeth to in case one is damaged. The teeth are protected by thin layers of skin which are pulled back when the viper ovens its mouth and unfolds its fangs to inject their prey with deadly venom.
Roughly 90% of the venom dry weight is protein, composed of a large variety of enzymes, polypeptide toxins and proteases. The enzymes include hydrolases (proteinases, endo- and exo- peptidases, phosphlipases) hyaluronidase and activators of inhibitors of the preys physiological mechanisms. Almost all venomos contain L – amino acid oxidases, phosophomono- and diesterases, phospolipase A2 and peptidases. Phospholipase A2 are the most wide spread of all snake venom enzymes, attacking mitochondria, red blood cells and leukocytes, peripheral nerve endings and skeletal muscles, causing haemorrhage, necrosis and flacid paralysis in their prey.
All Viperid venom act mostly hemotoxic and haemorrhagic, attacking both the prey clotting mechanism, causing tissue damage and persistent bleeding, or the victims blood pressure, causing the victim to die of shock, stroke or complete cardiac arrest. Although Viperid venom are relatively weak compared to some Elapids, the composition of their venom makes a bite highly uncomfortable and extremely painful.
Snake Venom Metalloproteases (SVMP) are a special type of protein consisting of Metalloprotease, disintegrin-like, and cysteine rich domains that are common in vipers and responsible for potent haemorrhages. They are associated with a wide range of functions but the plesiotypic effect seems to be the induction of haemorrhages. This is the result of proteolytic cleavage of basement membrane components present in capillary vessels, which likely result in the distention of the capillary wall, the disruption of the endothelial cell integrity, and, ultimately, extravasation.
These enzymes have evolved from a type of serine proteases and are almost exclusively found in the venom of viperid snakes. This toxin form contributes to the profound, rapidly developing swellings common after viperid envenomation. They do this mostly by binding to specific amino acid sites in substrates like lysine or arginine, which may alter the function of thrombin, a vital factor when it comes to blood clot formation. Additionally, venom kallikrein enzymes cleave to fibrinogen which is necessary to form a stable clot. By reducing the available fibrinogen for clot formation, haemorrhages are incudes and the victim starts to bleed into vital internal tissues.
I hope that you enjoyed this page and learned a bit from it. Pit Vipers are absolutely stunning and beautiful animals and they deserve to be treated as such. These snakes have climbed to the top of the tree of evolution and are, in my opinion, the ultimate predator when it comes to sophisticated and efficient hunting methods.
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