Snakes: Creatures Shrouded in Mystery
Introduction To These Snake FAQs
Have you ever had a question about snakes that you just couldn't find the answer for? Or maybe you've found an answer, but just didn't know if you could trust the information? Well, look no further! This article was written in an attempt to reliably answer some of the most frequently asked questions about snakes. You may utilize the "Table of Contents" below to help you quickly navigate to the section your particular snake-related question resides [by using your browser's "search" function (most often accessed by pressing "Ctrl+F" on your keyboard)]. The information presented herein is intended to be as accurate and succinct as possible, while providing some nice pictures and diagrams. Please see the "Disclaimer" section at the bottom of this page for more details on all of the content and materials presented here. If you believe that your snake question is not adequately addressed here or in the articles that I link to in my "Snake Venom" article series, then please feel free to ask your question in the "Comments" section at the bottom of this article and I will do my best to answer it and add that question/information to this article. Also, if you believe that any of the information contained in this article is lacking sufficient detail or is incorrect, then please leave a detailed comment addressing the issue and citing your sources (web links, books, journal articles, etc.). Thank you, and enjoy!
Table of Contents
Hint: use your browser's "search" function (most often accessed by pressing "Ctrl+F" on your keyboard) to quickly navigate to the section your particular snake-related question resides.
- What is the taxonomy of snakes?
- What is the taxonomy of venomous snakes?
- What about snake physiology and growth?
- What about snake skin?
- What about snake senses?
- What about snake skeletal and organ systems?
- What about snake teeth?
- What about snake venom?
- What about snake ingestion, digestion, and excretion?
- What about snake tails?
- What about snake reproduction?
- How does a snake move?
- Is there a difference between a Boa Constrictor and a Python?
- What are some characteristics of vipers?
- How can I easily identify front-fanged venomous snakes in the United States?
- Which snake is the most "venomous?"
- What are some snake records?
- What are some myths and misconceptions about snakes?
- Why are snakes worth keeping around?
What is the taxonomy of snakes?
Here is the commonly accepted phylogenetic tree leading up to snakes, including amphibians, lizards, and mammals as reference points:
<><>Class Amphibia (frogs/salamanders)
<><>Class Mammalia (mammals)
<><>Class Reptilia (reptiles)
<><><>Suborder Lacertilia (lizards)
<><><>Suborder Serpentes (snakes, >2,900 species)
What is the taxonomy of venomous snakes?
There are over 1,200 species of snakes in the world that can be considered "venomous." These snakes are thought to have descended from a single, common ancestor with rear-fangs. Here is the taxonomic breakdown of the venomous snakes:
>Suborder Serpentes (snakes, >2,900 species)
<>Superfamily Colubroidea (advanced snakes, >1,200 species)
<>>Family Atractaspididae (all venomous)
<><>Examples: Burrowing Asps, Stiletto Snakes
<>>Family Colubridae (some nonvenomous)
<><>Examples: many "common/typical" backyard snakes (at least in the U.S.)
<>>Family Elapidae (all venomous)
<><>Examples: Cobras, Coral Snakes, Sea Snakes
<>>Family Viperidae (all venomous)
<><>Examples: Vipers, Rattlesnakes
Snakes Can Thrive in Deserts
Albino Corn Snake
What about snake physiology and growth?
- Are snakes cold-blooded? Yes, they are ectothermic (cold-blooded) creatures that must rely on their environment to regulate their body temperature (e.g., either basking in the sun to increase temperature or moving into the shade to decrease temperature). This makes them up to 100 times more energy efficient than endothermic (warm-blooded) animals, leaving more energy available for growing and reproducing. This grants snakes the ability to thrive in "low-energy" environments (such as deserts).
- Are some snakes albino? Snakes are subject to many of the same color abnormalities (and the physical/mental handicaps that often accompany them) that several other organisms might experience as a result of random genetic mutations. This includes conditions such as albinism and melanism. Albino snakes are easily visible to predators and tend to have impaired eyesight and reduced motor/neural function, resulting in their very high mortality rate in the wild.
- Do snakes ever stop growing? No, they continue growing throughout their lives. The rate of this growth depends upon the metabolism of the snake, which can vary drastically based on a wide variety of factors (food availability, reproduction, environment, health, stress, species, etc.).
- How long do snakes live? Most species have a maximum (captive) lifespan of 15-25 years. Metabolism (not maximum size) directly impacts the lifespan of the snake, with lower metabolic rates (slower growth) resulting in longer lifespans. The process of "aging" is due to the accumulation of DNA damage and the shortening of telomeres (that protect the ends of chromosomes) with each cell replication (therefore, faster growth = faster degradation).
Snake Skin Layers During Ecdysis
Keeled Scales and Anal Plate
Heavily Keeled Scales
What about snake skin?
- Do snakes have skin? Yes, but their skin is covered and protected by a layer of scales.
- What are snake scales? Scales are thickened, keratinized areas of skin that serve to protect the snake and help it retain water. There are two layers of keratin in the scales: a hard, outer layer of β-keratin (beta-keratin; composed primarily of β-sheets) and a softer, inner layer of α-keratin (alpha-keratin; composed primarily of α-helices, but containing some β-sheets).
- Are there different kinds of snake scales? Yes, snakes can have scales that are smooth, "keeled" [where the scales possess a ridge down the center of the scale (much like the keel on the bottom of a boat)], or "granular" [where the scales are very 3-D and appear "bumpy" (like a hill) or pyramidal]. Keeled and granular scale morphologies give snakes a "rough" texture.
- Do some snakes have "horns" or "hair?" A number of snake species possess modified scales that have a "horny" or "hairlike" appearance. For example, the Eyelash Viper (Bothriechis schlegelii) has specialized scales around the eyes which resemble eyelashes, whereas the Gaboon Viper (Bitis gabonica) has specialized scales atop the anterior end of its head which resemble horns. These specialized structures are not actually composed of hair or bone.
- Are snakes slimy? To my knowledge, there are no snake species that secrete a mucous-like substance from their skin. Their skin may feel smooth or course (depending on the individual species and the morphology of the scales), but never slimy.
- Do snakes shed their skin all in one piece? Yes, they shed their skin all at one time in a process called ecdysis. Once the snake has constructed a new, inner layer of scales (keratin), a fluid is excreted between the new and old layers of scales in order to separate them. This fluid is then re-absorbed and the snake sloughs off its old layer of skin in a single piece (provided the snake is healthy and under optimal environmental conditions).
- Why do snake eyes turn blue before they shed? This occurs as a direct result of the fluid that is excreted by the snake to separate its new and old scale layers. This fluid makes the snake appear dull or bluish in color (greatly inhibiting their eyesight, making them more nervous/cautious) and more/less returns the snake to its normal color once it is reabsorbed (right before it actually sheds the old, outer scale layer). The excreted fluid, being composed of lactic acid and acid phosphatase, serves to hydrate and separate the layers by breaking apart the "glue" that holds the old and new scale layers together (e.g., desmosomes).
Different Kinds of Snake Eyes (Pupils)
Binocular Vision in Snakes
Mouth Anatomy of a Viper
What about snake senses?
- Do snakes have good eyesight? They can have a highly variable sense of sight, with arboreal (tree-living) species tending to have great binocular vision and fossorial (burrowing) species commonly having poor vision.
- Do snakes have eyelids? No, instead of having eyelids, their eyes are covered by a transparent scale (called a brille) that is replaced every time the snake sheds. This characteristic enables one to easily distinguish a legless lizard from a snake, due to the fact that all lizards (except geckos) have eyelids.
- Are snake eyes like human eyes? No, their eyes have re-evolved such that the lens is physically moved (by the iris muscles) to change focus, as opposed to all other tetrapods changing the curvature of the lens (using ciliary muscles, which are lacking in snakes) to accommodate. Snake eyes were "lost" in their fossorial ancestors (eyes are virtually useless underground) and secondarily re-evolved for returning to a terrestrial lifestyle.
- Can snakes see heat? Some snake species have heat-sensing pits or vents, which are capable of detecting less than a 0.01 degree Fahrenheit difference in temperature. These heat-sensitive organs couple with their eyesight and sense of smell (forked tongue) in order to get a very precise direction and distance to their target.
- Do snakes have a good sense of smell? Although snakes have nostrils, they are granted a great sense of smell due to the action of their forked tongues, which "taste" the air. Each fork of the tongue is inserted into a different chamber of the Jacobson's organ in the roof of the mouth. This allows the snake to pick up scent particles in the air in a direction- and concentration-dependent fashion, which tells the snake where and how far its target is.
- Do snakes have ears? No, they lack external or middle ears, giving them a poor sense of hearing. They do, however, have inner ears that enable them to sense vibrations through the air or substrate using bone conduction.
What does a snake skeleton look like?
Snake Internal Anatomy
What about snake skeletal and organ systems?
- Do snakes have bones? Yes, snakes are vertebrates. A snake’s skeleton is principally composed of a skull, ribs (as many as 500 in some species), and highly flexible vertebrae [most of which are connected to two ribs, all the way back to the region of the cloaca (caudal/post-cloacal vertebrae are either devoid of ribs or have small ribs for a short distance from the cloaca)].
- Do snakes have legs? Although most snake species lack hindlimbs and a pelvic girdle, all snakes lack forelimbs and a pectoral girdle. Some of the more "archaic" species of snakes (such as pythons, boas, and blind snakes) possess a pelvis and vestigial remnants of femurs (commonly in the form of anal/pelvic/cloacal spurs, which protrude from either side of the cloaca). Having reduced/absent limbs is not unique to snakes, but has actually evolved at least 62 independent times in members of Order Squamata (snakes and lizards), with ~25 times occurring in Skinks, alone.
- What internal organs do snakes have? They have many of the same organs that humans possess, such as a stomach, liver (often the largest organ), lungs, kidneys, adrenal glands, spleen, pancreas, intestines, gall bladder, gonads, and a thyroid gland. They have three-chambered hearts (two atria and one ventricle) and lack a diaphragm (relying on body action to pump air in and out). Their vital organs have become long and slender in order to comfortably fit in their tube-like bodies.
- Do snakes only have one lung? Depending on the species involved, the left lung tends to be reduced in size or absent, with an enlarged right lung. Some of the “archaic” snakes (such as pythons and boas) have two functional lungs, whereas some of the “advanced” snakes (such as rattlesnakes) only have one lung. This is another way to tell legless lizards from snakes, as they have evolved to “prefer” their left lung, with a reduced/absent right lung.
What about snake teeth?
- What kind of teeth do snakes have? They have needle-like (long, slender) independent teeth (teeth that are not connected to other teeth; like in humans) that are slightly curved inward and replaced continuously throughout their lives. Snakes have subpleurodont dentition, meaning that their teeth are attached to a large ridge (called a pleura) of the jawbone on the labial side (facing the lips/cheek) and are attached to a low bony ridge at the base on the lingual side (facing the tongue). This bone arrangement forms a shallow pocket (called a theca) that each tooth rests inside of.
- Are all snake teeth the same? It depends on whether or not they are venomous. Snake teeth are either homodont (all teeth are similar in size, shape, and function) or heterodont (possessing a pair of specialized "fangs" for injecting venom), depending on the species.
- What are snake fangs? Fangs are specialized teeth designed to introduce venom into prey and predators.
Cobra Fangs: Normal vs Spitters
Venom Injection by Front-fang
Venom Injection by Rear-fang
What about snake venom?
- What is in snake venom and what envenomation symptoms might be caused by snakebite? Snake venom can be surprisingly variable, so it can be difficult to predict exactly what compounds are present in it and what effects a human may suffer from an envenomation. You may refer to the following article, which discusses these topics in some detail: Snake Venom Composition/Variability.
- Can snakes “spit” their venom? Only around 16 species of snakes can manage this feat with some level of proficiency, with the ability to spit having evolved independently on at least three occasions. Several Cobras (genus Naja) and the Rinkhals (genus Hemachatus) have specialized fangs with a forward-facing (instead of downward) venom exit hole. This exit hole is higher up on the fang (not reaching down to the tip), closer to the center face of the fang (instead of off to the side), circular/tear-shaped (instead of diamond/oval-shaped), rifled (to increase accuracy/range), and angled “inward” towards the center line of the snake’s head (such that the ejected venom streams from each fang cross over at a certain distance). Some of the more proficient spitters are capable of ejecting a surprisingly accurate venom spray (targeted at the eyes/face) up to a distance of 10 ft away. The snake may attempt to modulate how much air is expelled during spitting in order to adjust the spread of the aerosolized spray to the size of the face. Once in the eyes, the venom is capable of causing extreme pain and blindness. The Mangshan Pitviper (Protobothrops mangshanensis) is reported to have some ability to “spit” venom, but this has not been scientifically verified and could just be the result of loose venom droplets being propelled forward by the snake’s forcefully exhaled air during a hiss.
- Are rear-fanged snakes dangerous? Most species of rear-fanged snakes are relatively harmless to people because their venoms are not typically dangerous towards humans and they are incapable of effectively injecting large quantities of venom in a bite (without holding on for a significant period of time). The following article discusses this topic in detail: Front- and Rear-fanged Snake Envenomation Systems.
Some Snakes Eat Other Snakes
Prey Handling: Constriction
Prey Handling: Live Consumption
Snake Gape Size
What about snake ingestion, digestion, and excretion?
- What do snakes eat? They are carnivorous and ingest other creatures (preferably alive or freshly killed). They can acquire prey by constricting (wrapping around them and squeezing), injecting venom, simply overpowering them, or a mix of all three. Snakes are capable of digesting virtually anything but hair (which is occasionally excreted in the form of "hairballs" along with the "normal" waste). Many snakes are capable of eating other snakes and some species even specialize in such behavior (these snakes are often called Kingsnakes).
- Do snakes chew their food? No, snakes ingest prey whole without chewing to break it into smaller pieces first. Snake teeth are designed to grab and hold onto prey until it is swallowed, not chew.
- Can snakes consume eggs? Some species are capable of swallowing eggs. A few species even possess a vertebral projection in their esophagus that enables the snake to crack the eggshell in their throat, squeeze the contents out into their stomach, and then regurgitate the leftover bits of shell.
- How do snakes breathe while swallowing large prey? The anterior portion of the trachea, which resides along the bottom of the mouth/throat, is very strong/mobile and may be extended out of the mouth, beneath the prey being swallowed, to facilitate breathing during ingestion (which, in the case of very large constrictors, is a process that may take over an hour).
- How far can snakes open their mouths? They tend to have highly kinetic skulls (up to 150 degree opening) for swallowing large prey whole. Fossorial snakes, however, tend to have much more rigid skulls that cannot open very far. Most snakes have highly flexible lower jaws (due to the fact the left and right lower jawbones are often not connected) and very stretchable skin, enabling them to effectively wrap their mouths around large prey.
- Do snakes always eat their prey head-first? Generally, yes. This is because the bodies of most animals are oriented in a head-to-tail fashion, meaning that swallowing prey in that manner will permit everything to go down the snake's throat much smoother. Their forked tongue helps them locate the mouth of incapacitated prey so that they can ingest them head-first.
- Where and how do snakes poop? They possess a cloaca for excreting waste in the form of uric acid (and, on occasion, bits of undigested hair in the form of "hairballs"). The cloaca is a unified orifice for excreting both solid and liquid waste. It is oriented in a transverse fashion (not longitudinal, like in most tetrapods), meaning that if you were to pick up a snake from the head (allowing its body to dangle straight down) and look at the underside of its tail, the cloacal opening would be horizontal. The cloaca is covered by a specialized, half-moon-shaped scale called the anal plate (which can be single/intact or divided, depending on the species). Uric acid is an efficient form of solid waste that reduces water loss. The amount of liquid (urine) excreted with the uric acid varies between species.
What does snake poop look like?
Intact and Broken-off Rattles
What about snake tails?
- What is considered the "tail" of a snake? The tail is the portion of the body from the cloaca to the end of the snake. Tail length varies based on species (and gender in some species) and total body length. Whereas legless lizards nearly always have long tails (most vertebrae are post-cloacal), snakes often have short tails (most vertebrae are pre-cloacal). Ventral scales on the tail are called post-cloacal or caudal scales and can either be single/intact (one scale row) or divided (two scale rows).
- Can snakes re-grow their tails? They tend to be capable of losing their tails with twisting and force (a process called pseudautotomy, where the tail breaks in between the vertebrae and is not under conscious control of the snake), but aren't capable of regenerating them.
- What is a snake rattle? Rattles are constructed of a series of interlocking segments of keratin (often referred to as "rattles"), located at the end of a Rattlesnake's tail. Rattlesnakes are the only snakes to have this unique adaptation, which they vibrate vigorously (at a muscle twitch rate faster than any other vertebrate) to ward off potential predators. Rattlesnakes are strictly limited to the Americas. A single rattle segment is added each time the snake sheds by making a "cast" inside of the button (i.e., basal rattle) at the end of the tail.
- Can you tell the age of a snake by the size of its rattle? Not necessarily. Rattles can be relatively fragile and break off with some frequency. The rate at which a rattle grows in size (number of segments) is dependent upon how often the snake is shedding, which primarily relies on the snake’s age, health, and feeding frequency. Snakes can shed approximately 8 times a year during their first year of life, but may slow down to less than half of that during their adult life. You can, however, determine if a snake has lost/damaged its rattle since birth by looking for an intact "terminal button" on the end of the rattle.
- Do snakes secrete musk? Many snakes have musk glands and are capable of excreting a smelly fluid (called musk) from their cloaca in order to ward off predators. Some species (e.g., Rattlesnakes) can even aerosolize concentrated musk a couple of feet away in a manner similar to a skunk.
- Do snakes secrete pheromones? Some species are known to produce pheromones in their skin or from scent glands in their tail for use in communication and reproduction.
Snake Parental Care
Tail of a Male Snake
Male versus Female Tail Length
What about snake reproduction?
- Do any snakes show parental care? A few species do. Rattlesnake mothers may care for their young (defend, roundup, etc.) up until the babies shed for the first time. Some python mothers are known to wrap around their eggs to protect and incubate them (by “shivering” their muscles to create heat) until they hatch. King Cobra (Ophiophagus hannah) mothers are actually known to create a mound, or "nest," of decaying matter to incubate their eggs. King Cobra mothers will often aggressively defend their nest until a couple of days before the eggs hatch (supposedly to prevent the mother from eating the babies, as King Cobras are cannibalistic). Most snake species, however, demonstrate minimal, if any, parental care.
- Do snakes lay eggs or have live young? Depending upon the species, snakes can either be oviparous (lay leathery eggs) or ovoviviparous (retain eggs until they "hatch" inside of the mother and the live young are "birthed").
- Does temperature determine whether snake babies are male or female? No, their gender is genetically determined (not temperature-dependent as in Crocodilians). Males have ZZ chromosomes (as opposed to XY in humans) and females have ZW chromosomes (as opposed to XX in humans).
- Is it possible for a snake to reproduce by itself? Although snakes tend to utilize sexual reproduction, certain species/populations/individuals may undergo asexual reproduction via parthenogenesis. This means that a female snake can have a "virgin birth" by way of creating half-clones of herself (due to a mistake during oogenesis, whereby a polar body can act as a sperm and fertilize the egg). This is the only way that female offspring with WW chromosomes can be created in nominal amounts.
- Do male snakes have a penis? Well, actually, male snakes have a pair of copulatory organs called hemipenes. These hemipenes are basically outpocketings of the end of the cloaca (within the tail) that are everted from the cloaca before copulation. The fine structure (spines, ridges, and ornamentation) of these hemipenes is often used as an "easy" way of identifying a species, as it tends to have a higher rate of evolution than many other physical traits. Males only insert one of their hemipenes into the female snake's cloaca at a time, where a groove in the surface of the hemipenis (called the sulcus spermaticus) transports sperm into the female.
- Is there an easy way to tell a male snake from a female snake? Some species are sexually dimorphic, where the males possess longer tails (relative to total body length), a different body coloration than the females (e.g., Boomslang males are green, whereas females are brown), or don't grow to be as large as females. In species that possess cloacal spurs, males possess larger and more mobile cloacal spurs than females. Males also tend to have tails that taper slowly (due to the presence of the hemipenes), whereas females have tails that taper quickly. In many cases, however, the only way to tell for sure is by “probing” the animal [with the probe traveling much further down the tail in males (within the hemipenal pocket) than in females (e.g., traveling 10 scales in males and 2 scales in females)].
A Snake that "Flies"
How does a snake move?
Snakes can move a variety of ways, dependent upon the species, substrate, and the individual snake's needs at the time. The following are seven common ways that snakes can move, preceded by the questions that one might ask when seeking knowledge of that particular mode of locomotion.
- How do snakes "normally" move? Can snakes swim? Lateral Undulation: When crawling on a substrate with objects in the environment, snakes will tend to move using lateral undulation, also known as serpentine locomotion, which is the "typical," s-shaped way for snakes to move. This consists of the snake not only pushing off of the ground beneath its body, but also pushing off of the sides of the objects in its environment, giving the snake increased speed and agility (often granting it the ability to out-maneuver humans and other potential predators). To clarify, this process involves the snake pushing posterolaterally off a variety of pivot points in the environment in order to move forward in a continuous manner (with no recovery phase). Lateral undulation is also commonly utilized while the snake is swimming in water. This mode of locomotion does not involve any static points of contact with the substrate.
- Can snakes move on a smooth, solid surface like glass? Slide-pushing: While crawling on low-friction substrates, snakes can utilize slide-pushing. This consists of the snake using rapid, alternating waves of body motion to generate a "sliding friction" that propels the snake forward. To clarify, this process involves the snake using seemingly non-productive movements to "flail" itself forward on a slippery substrate. This mode of locomotion does not involve any static points of contact with the substrate.
- Can snakes move in a straight line? Rectilinear: While crawling on a stable substrate devoid of objects, snakes will tend to move using rectilinear locomotion, also known as "rib-walking." This consists of the snake using its ribs and associated muscles to push itself up off of the ground and forward in a more-or-less straight line (making it appear as though the ribs are "walking" when seen from the side, almost like an inchworm). To clarify, this process operates on a small scale whereby the snake pulls its skin forward and then brings the ribs and body up to the skin using the ventral scales as a stationary anchor. This is the only mode of snake locomotion to use synchronous muscle contractions and involves several points of static contact with the substrate. This locomotion is most commonly seen in large, heavy-bodied snakes.
- Can snakes climb trees? Concertina: When attempting to climb up a tree or move across a low-friction surface, snakes will often utilize concertina locomotion, which is similar to the movement of an accordion. This consists of the snake reaching its head and neck up the tree to start wrapping around it, getting a firm wrap using the front portion of its body, then bringing up the rest of its body, loosening up the front portion while tightening the back portion of its body, and reaching up to the next point and repeating the process (hence, going from a spread-out state to a bunched-up state, like an accordion). To clarify, this process involves the snake establishing a stable platform with the front part of its body, then bringing up the rest of its body to establish another stable platform, enabling the front part of the body to release and extend to establish another platform. This mode of locomotion involves static points of contact with the substrate. Concertina locomotion is slow-going and energetically costly (requiring up to 7 times more energy than lateral undulation).
- How do snakes move across sand? Sidewinding: While crawling on a low-friction or shifting substrate devoid of objects, snakes will tend to move using sidewinder locomotion. This is a complicated motion whereby the snake utilizes its own momentum to propel itself forward using a series of lateral "body throws" (in the form of “loops”) initiated by the head/neck and followed through by the body, resulting in the appearance of a series of independent (not connected), s-shaped "footprints" in the substrate (which are oriented at an angle to the net direction of motion). To clarify, this process involves the snake applying force in a predominantly downward fashion (to avoid slipping) to lift a portion of its body, move it forward, and set it down (making it appear as though the snake is wildly throwing body loops angled to the side at random). This mode of locomotion tends to involve static contact with the substrate at two points and can be utilized by a number of species of snakes (not just Sidewinder Rattlesnakes).
- Can snakes jump? Saltation: When a snake needs to cross a distance quickly, it may opt to use saltation (jumping). This is basically a modified form of concertina locomotion, where the snake rapidly straightens its body in an anterior to posterior fashion while lifting its entire body off of the substrate. To clarify, this process consists of the snake jumping (or faux striking) and throwing its entire body forward, lead by its head. Saltation is a rare form of locomotion that is primarily utilized in aggressive or escape behavior. This mode of locomotion involves static points of contact with the substrate.
- Can snakes fly? Gliding: Constrained to a select few species, these snakes are capable of a limited form of flight called "gliding." This is where the snake "leaps" from atop a tall object (e.g., tree) and glides safely down to the ground (typically traveling much further laterally than vertically). To clarify, this process consists of the snake "jumping" off of the tall object (to "catch" the air), making its belly concave (instead of convex) to create an air-foil (similar to a plane wing or parachute), moving its body in a way similar to lateral undulation (to propel the snake forward), and using its tail as a rudder to direct its final trajectory (on the ground or another tree).
Heat Vents in Pythons
Dorsal Head Scales
Is there a difference between a Boa Constrictor and a Python?
Yes, there are several differences between them. We will go on to evaluate and present both similarities and differences between boas and pythons.
- Are boas and pythons the same? No. Although they are both part of family Boidae, they comprise different subfamilies. Boinae is the subfamily of Boa Constrictors, Erycinae is the subfamily of Sand Boas, and Pythoninae is the subfamily of Pythons (Note: although the taxonomy of these snakes has changed in recent years, it is most convenient to utilize this older phylogeny in order to adequately compare their characteristics as presented here).
- Are boas and pythons constrictors? Yes. All members of family Boidae are capable of using their body muscles to constrict their prey. Constriction is used to suffocate and/or crush prey in order to overpower/incapacitate/kill them before safely ingesting them.
- Do boas and pythons have cloacal spurs? Several species of snakes within family Boidae possess the remnants of femurs and a pelvis. These cloacal spurs, larger in males than in females, are often used by male snakes to “tickle” the female snake into a position that is conducive to copulation and are sometimes utilized in male-male combat.
- Do boas and pythons lay eggs? Although pythons are oviparous (lay eggs), boas are ovoviviparous (give birth to live young).
- Do boas and pythons have heat receptors? Many species (except for the Sand and Rubber Boas) possess heat-sensing vents on their upper/lower labial scales. They are recessed from the scales around them and can be a variety of colors (red to pink to grey). Although the labial vents in Boa Constrictors are located between the scales (commonly oriented along the side of the labial scales), the labial vents in Pythons are located within the scales (commonly oriented along the top of the labial scales).
- Do boas and pythons have the same-sized scales in the front half of the top of their heads? No. Pythons have large dorsal head scales, whereas Boa Constrictors have small dorsal head scales, and Sand Boas possess intermediate-sized dorsal head scales. Although this is kind of relative, if you were to count the number of scales between the eyes, you would only count ~4 scales between the eyes of adult Pythons, and ~20 scales between the eyes of adult Boa Constrictors (meaning that Python head scales can be about five times as large as those of Boa Constrictors).
- Can boas and pythons be found in the same areas of the world? Yes. Although North America only has Sand Boas, Central/South America only has Boa Constrictors, Europe only has Sand Boas, Australia and Southeast Asia only have Pythons, Africa, Indonesia, and the rest of Asia have a mixture of the three subfamilies.
Heat-sensing Pit Organ Anatomy
Pitviper Heat Pits vs Nostrils
What are some characteristics of vipers?
- What snakes are considered “vipers?” All members of family Viperidae, including the Old World Vipers (2 subfamilies, notably Viperinae), Pitvipers (subfamily Crotalinae), and Rattlesnakes (genera Crotalus and Sistrurus within subfamily Crotalinae).
- Do all vipers have folding fangs? Yes, they all possess long front-fangs that fold up along the roof of their mouth when not in use (due to a rotatable maxilla).
- Do vipers have hemotoxic venom instead of the neurotoxic venom of elapids? Venom composition is not as "cut-and-dry" as that due to the fact that several vipers possess “neurotoxins” and several elapids possess “hemotoxins.”
- Are adders vipers? Although many adders, such as the European Adder (Vipera berus) are vipers, Death Adders (genus Acanthophis) are actually elapids that have undergone convergent evolution to act, look, and possess physiology similar to, a viper. This means that Death Adders are ambush predators with thick bodies, arrow-shaped heads, vertical pupils, and fangs that have evolved to become surprisingly long and mobile.
- Do vipers lay eggs or have live young? They can either lay eggs (oviparous) or bear live young (ovoviviparous). All Rattlesnakes have live young.
- Can vipers see heat? Pitvipers are named because they possess forward-facing heat-sensitive pits between their eyes and nostrils. Rattlesnakes, being a subset of Pitvipers, possess these pits, but Old World Vipers lack heat-sensitive pits.
- Which state has the most venomous snakes? Arizona exhibits the most taxa (species and subspecies) of front-fanged venomous snakes in the U.S., having 19 snakes, all but one of which are rattlesnakes.
How to ID Coral Snakes in U.S.
Iconic American Venomous Snake
How can I easily identify front-fanged venomous snakes in the United States?
The U.S. has only a couple of species of elapids, all being Coral Snakes (genera Micrurus and Micruroides). Although a few species of king- and milk-snakes mimic the colors and patterns of Coral Snakes, there is a relatively easy way to ID Coral Snakes (in the U.S.) based on the arrangement of colored rings on the snake’s body: If red touches black, venom lack (is a nonvenomous king/milk-snake), but if red touches yellow, it kills a fellow (is a venomous Coral Snake). In many of these snake species (venomous or harmless), yellow-colored rings are actually white.
In order to help ID vipers in the U.S., the following “rules” are presented. Note that these rules are most effective for ID’ing Rattlesnakes, slightly less effective for ID’ing Pitvipers (because they lack a rattle at the end of their tail), and are not at all effective at ID’ing Coral Snakes. All “rules” possess exceptions, but generally serve as a quick-and-easy guide to identifying vipers.
- Does the snake have a rattle? All rattlesnakes (genera Crotalus and Sistrurus) are venomous and have a distribution limited to the Americas. Many non-rattlesnakes are capable of rapidly shaking their tail against the ground (preferably dead leaves or dry substrate) in an effort to imitate a “rattling” sound and mimic rattlesnake behavior in order to intimidate/warn predators. In addition, it is possible that the snake may have lost the end of its tail by an injury or may not have been born with a rattle as the result of a genetic defect.
- Does the snake have an arrow-shaped head? An arrow-shaped head generally stems from two things: venom glands and jaw muscles. Vipers have large venom glands on the sides of their heads. Vipers also commonly have the ability to strike quickly and with a lot of force, which is partially derived from their large jaw muscles (some of which are associated with the venom glands). Many non-vipers have the capacity to flatten-out their heads in an effort to make them appear larger and more intimidating to potential predators.
- Does the snake have vertical pupils? All rattlesnakes and vipers have vertical pupils, but there are also a few rear-fanged venomous (~harmless) snakes that have them [e.g., Night Snakes (Hypsiglena torquata) and Lyre Snakes (Trimorphodon biscutatus)]. Although vertical pupils tend to be found in snakes with nocturnal activity, they are more strongly associated with the hunting behavior of the snake (being found more often in sit-and-wait ambush predators). Vertical pupils permit the snake to keep a wide horizontal field in focus without having to move its head and give away its position. This is a trait that has evolved independently several times in many different groups of snakes and may aid in camouflage (by mimicking grass) and reduce the amount of glare in daylight. The caveat is that vertical pupils have the capacity to enlarge in darkness (in order to allow more light to enter the eye) to such a degree that they can appear to be round pupils.
- Does the snake have heat-sensitive pits? All vipers in the U.S. are Pitvipers, so they will be the only snakes with a pair of forward-facing heat-sensitive pits located between the eyes and nostrils. Nostrils can be distinguished from heat pits because they are often lateral-facing (making them difficult to see from the front), not reflective when a light is shined upon them, positioned at the end of the nose, and smaller than heat pits.
- Does the snake have a single row of post-cloacal scales? All U.S. vipers have intact ventral scales on the underside of the tail (a single row of post-cloacal scales), whereas any other snake (except for elapids) has divided ventral scales on the underside of the tail (two rows of post-cloacal scales).
Taking all of these things into account means that only some of these "guidelines" are truly reliable in easily identifying rattlesnakes: the presence of a rattle, heat-sensitive pits, and a single row of post-cloacal scales. Vertical pupils and an arrow-shaped head are characteristics that are often too relative and/or subjective to be useful.
How to Quickly/Easily ID Pitvipers in the U.S.
Black Mouth Color for Defense
Snake with Largest Fangs and Most Venom
Which snake is the most “venomous?”
This is a very broad/complicated question, so we will break it down into several specific questions, instead. All of the world’s most dangerous snakes are front-fanged venomous.
- Which snake kills the most people? This is likely the Saw-scaled Viper (genus Echis), which kills 1,000’s of people every year.
- Which snake’s venom kills people the quickest? This is likely a species of Cobra (genus Naja), many of which possess fast-acting neurotoxins in their venom that can paralyze the diaphragm and cause death by asphyxiation within 30 minutes.
- Is there a snake whose bite means certain death without antivenom or hospital care? Yes, the Black Mamba (Dendroaspis polylepis) has a 100% mortality rate in humans without supportive medical care (either to administer antivenom or to breathe for you when the potent neurotoxins take effect and cause your diaphragm to stop working).
- Which snake has the most toxic venom? Drop for drop, the Inland Taipan (or Fierce Snake, Oxyuranus microlepidotus) has the world’s most toxic venom towards mice, with an LD50 of 0.01 mg of venom per kg of mouse body weight [reported in the form of 0.01 mg/kg (milligram per kilogram) or 0.01 ug/g (microgram per gram); ref #1]. Interestingly, there are no confirmed human casualties from this species. People often claim that certain species of sea snakes are the most toxic snakes, but the Belcher's Sea Snake (Hydrophis belcheri) "only" has an LD50 of 0.24 mg/kg (ref #3; similar to the Black Mamba, Dendroaspis polylepis, with an LD50 of 0.264 mg/kg; ref #2), the Beaked Sea Snake (Enhydrina schistosa) has an LD50 of 0.164 mg/kg (ref #1), and the Olive Sea Snake (Aipysurus laevis) has an LD50 of 0.12 mg/kg (ref #3).
- Which snake has the most venom? The Gaboon Viper (Bitis gabonica) is capable of producing the highest venom yield, with up to 9.7 ml of venom (equal to 2.4 kg or 5.3 lbs of dried venom) from a single snake.
Longest Snake in the World
What are some snake records?
- What is the largest snake in the world? This is a complicated question, so we will break it down into two, more specific, questions.
- What is the longest snake in the world? Among extant (opposite of extinct, meaning still living today) snakes, the Reticulated Python (Python reticulatus) grows to be the longest snake. From Southeast Asia, it is a terrestrial/semi-arboreal predator known to reach 33' long and 440 lbs. The longest one maintained in captivity was an 8 year old snake named Medusa that was just over 25' long and 350 lbs.
- What is the heaviest snake in the world? Among extant snakes, the Green Anaconda (Eunectes murinus) grows to be the heaviest snake. From South America, it is an aquatic ambush predator known to reach 28' long and 550 lbs.
- Which venomous snake is the longest? The King Cobra (Ophiophagus hannah) reaches just over 18’ in length.
- Which venomous snake is the heaviest? The Gaboon Viper (Bitis gabonica) can get up to 44 lbs.
- Which venomous snake has the longest fangs? The Gaboon Viper (Bitis gabonica) can grow fangs up to 2.2” long.
- What is the biggest snake to have ever lived? The Titanoboa (Titanoboa cerrejonensis) lived ~60 million years ago and grew to b