A Pit Viper Snake Can 'See' You, Even in the Dark

"There are currently 260 species of pit vipers recognized by science," says herpetologist Emily Taylor via email. Many reside in North and South America, though the subfamily also extends into parts of Southeast Asia.

Besides rattlers, the list of pit vipers includes cottonmouths, copperheads and the bushmaster snakes.

The name "pit" vipers derives from the heat sensitive holes (i.e., pits) located between their eyeballs and nasal openings. "Pit vipers are distinguished by the two infrared-sensing pits on their faces. Other snakes lack these pits and also lack the ability to sense infrared radiation," says Taylor.

Wildlife biologist Andrew Durso explains in an email that while "boas and pythons also have pit organs," the "structure is different, although the function is the same."

Discovered in the year 1800, infrared radiation, also called "IR" or "infrared light," is a type of radiant energy on the electromagnetic spectrum that's invisible to the human eye.

You're giving off IR right now. Every object in the universe with a temperature above absolute zero (i.e., -459.8° Fahrenheit or -273.15° Celsius) emits some amount of infrared radiation. Things that are physically warmer give off more IR; our bodies feel that energy as heat. Like night-vision goggles, the viper's pit organs are used to detect IR.

According to Durso, these structures are "essentially very simple eyes that see in the infrared spectrum. They have a narrow opening leading to a wider cavity, in the middle of which a membrane filled with infrared receptors is suspended away from the body, acting as a retina."

This lets the heat sensitive snakes essentially produce thermal images of nearby animals. Since many pit vipers go hunting after dark for rodents, birds and other creatures warmer than themselves, it's a helpful superpower.

"Their [real] eyes do not sense this radiation," Taylor explains. "However, the sensory information from their eyes (photoreception) and their pits (thermoreception) is likely 'merged' in their brain in some way."

"It's impossible to know for sure what it looks like to the snake, but it's likely that they combine the input from their eyes and from their pit organs into some sort of dual image," she adds.

When dinner's in sight, vipers lash out with sophisticated fangs. Hinged and capable of moving independently, these are long, tubular teeth. And they're hollow, too: Venom is released through a slit near the tip.

"Snake venoms are cocktails of thousands of chemicals, mostly proteins that disrupt physiological pathways in the prey," says Taylor. Biological toxins fall into a number of different categories. Two of the major groups are known as hemotoxins and neurotoxins.

Pit Viper Venom Effects

"Hemotoxins," Taylor informs us, "disrupt the coagulation of blood and cause severe internal bleeding." Meanwhile, neurotoxins are built to "interfere with normal nervous system functions at multiple levels, for example by blocking neurotransmitter release or reuptake or by preventing neurotransmitters from binding."

After venomous snake bites, hemotoxic infection will cause cell destruction and tissue necrosis, while neurotoxin numbs the prey to pain and eventually stops the body's motor functions. "The result is that muscles cannot contract, and envenomated prey often die when their diaphragm, which is the main muscle used for breathing, can no longer contract," says Taylor.

Depending on the snake species, a given snake might be able to inject you with both kinds of toxin. "Many venomous snakes, including pit vipers, have multiple hemotoxins and neurotoxins [in their venoms]," Taylor notes.

Ambush hunting is a pit viper specialty. Most of the time, the snakes wait for their warm blooded prey to come to them instead of chasing it down. Why waste energy?

When a pit viper lashes out, the reptile can strike with up to half of its total body length. Some have been clocked moving their heads at 8 feet (2.4 meters) per second in the process.

That's not to say they always hit the target. Experiments involving Gloydius shedaoensis, a Chinese pit viper, show that adults strike more accurately than juveniles. Halfway around the world, kangaroo rats can use evasive maneuvers to dodge a Mojave rattlesnake in mid-strike.

At least one species, roadrunners, actively goad rattlesnakes into striking. The famous birds eat small rattlers, despite having no natural resistance to pit viper bites or snake venom.

A roadrunner's first move is to pester one of these snakes until the reptile tries to strike back. Then — while the snake's body is fully extended — it'll grab the head. Before our rattler can react, its attacker bashes its skull against the ground. Red-tailed hawks employ a similar strategy.

Pit vipers are also killed by nonvenomous king snakes who hunt and swallow rattlers, cottonmouths and copperheads whole.

Humans would do well to keep their distance. While snake bite fatalities are extremely rare in the United States, pit viper envenomations may lead to severe signs like shock, swelling, bruising, blistering, paralysis and other delightful symptoms.

After encountering snake bites, it is crucial to seek antivenom administration as quickly as possible.

We'll leave you on a more pleasant topic: babies. Although some pit vipers lay eggs, the majority give birth to live young. Certain rattlers can deliver as many as 25 infants per litter.