— This article by Jerry Cates, first published on 7 March 2010, was last revised on 23 October 2013. © Bugsinthenews Vol. 11:03(13).
Note: Most of the photos shown on this page were provided by viewers who, in return for identifying the specimen photographed, granted exclusive use of their images. In turn, permission is hereby granted for all lawful, non-commercial uses by our viewers, so long as attribution and a link to this website is provided with each use.
Does the above pattern say anything to you? If you see a snake with these markings on a trail, will you know to give it a wide berth? Using the material that follows you will learn to tentatively identify snakes by their markings and coloration, and — in particular — to distinguish between dangerous and non-dangerous snakes quickly. Numerous photos, like the one above, are included for that purpose. These photos are constantly added to, so come back to this page frequently. The more often you peruse these images, the more likely you will make the right decision when out in the wild.
Basic Guide to North American Snake Markings and Patterns:
Several basic patterns are officially recognized by herpetologists who study and write about snakes. However, the nomenclature is not precisely defined, probably because so many variations present themselves in snake specimens found in the wild. Besides the small number of official descriptors, many other expressions are used by herpetologists in an unofficial, almost off-hand way, to characterize the snakes they write about. In the material that follows, an attempt is made to include this wider range of descriptors and relate it to the accepted list. Keep in mind that this is an evolving process and, with your help, will continue to improve over time.
Ranking a Snake’s Potential to Inflict Injury on a Human Handler:
In the material below, the expressions “venomous,” ”mildly venomous,” ”non-venomous,” or “harmless/inoffensive,” are used with each species of snake. This designation scheme is — unfortunately — quite crude, but is intended to provide at least some indication of the danger or lack thereof regarding the snake’s venom, dentition, and defensive behavior.
VENOMOUS (i.e., by definition DANGEROUS): A venomous snake, for our purposes here, is one that has true venom glands that produce a highly toxic venom, and a specialized venom delivery apparatus in the form of forward-facing, hollow, or canal-like fangs.
“Venomous”? or “Poisonous”? It is not unusual for many, even those recognized as authorities within the field of herpetology, to refer to venomous snakes as being “poisonous.” That expression, though in vogue in earlier times, is today used more often to refer to things, living or dead, animate or inanimate, that induce poisoning when ingested, rather than to living animals that inject a poison by biting or stinging. By contrast, the expression “venomous” expressly refers to animals that typically poison other animals by biting or stinging them. For that reason it is preferred by most, though not all, modern herpetologists when referring to snakes that inject venom into their prey.
Still, despite the obvious etymological distinction between these terms, one’s choice of which to use in spoken or written communications is not an accurate test of one’s herpetological competence. Scientific literature exhibits many a renowned herpetologist who refers to venomous snakes as “poisonous.” Some, in fact, continue to use the reference today. Dr. Edward O. Wilson, professor emeritus at Harvard’s Museum of Comparative Zoology and a two-time Pulitzer Prize-winning author, is recognized as one of the world’s foremost authorities on snakes; in his writings, however, he is especially fond of the term.
In North America, the native venomous snakes include all the rattlesnakes, copperheads, the cottonmouth, and the coral snake. The rattlesnakes, copperheads, and the cottonmouth all have erectile, hinged, hollow fangs, relatively large venom reservoirs, and efficient venom injection musculature. The coral snake has short, fixed fangs with venom grooves (or canals), a relatively small venom reservoir (lumen), and a comparatively weak venom injection musculature; these ”deficiencies” are, however, more than compensated for by the coral snake’s highly toxic venom.
Question: Are venomous snakes beneficial members of earth’s ecosystem?
Answer: Yes, because they — along with many of our mildly-venomous and non-venomous snakes — prey on rodents, which are among the most destructive pests found on the planet, and help keep their populations in check. Whenever all the snakes in an ecosystem — venomous and non-venomous species alike — are removed or their populations are reduced, rodent populations immediately soar, allowing their destructive habits to wreak a havoc of monumental proportions. The resulting economic loss, not only to humans but also to other organisms that rely on grains, nuts, and seeds for sustenance, can be enormous. In areas of limited human populations, venomous snakes should probably be protected under most circumstances. However, many herpetologists agree that in areas with moderate to dense human populations, venomous snakes have little or no economic value (they compete with non-venomous snakes for existing rodent populations) but instead pose serious physical and economic risks to the area’s human inhabitants and their pets. Concerted efforts to eliminate venomous snake species (as in annual rattlesnake roundups) do not appear to adversely impact rodent control measures in the same area, because competing non-venomous snakes (which should — at all costs — be protected everywhere) take up the slack. Experiences in places where annual rattlesnake roundups are carried out (as in Sweetwater, Texas) suggest that the impact on rattlesnake populations is not sufficient to endanger the endemic rattlesnake populations, though it does reduce those populations somewhat. Such roundups do, however, lead to larger populations of non-venomous snakes, and result in a reduction in venomous snake and rodent populations, according to some authorities.
MILDLY VENOMOUS (which are, by definition, essentially NON-DANGEROUS): A mildly venomous snake’s saliva, produced by modified salivary glands, is mildly toxic, but such snakes generally lack the dentition, jaw architecture, and venom injection musculature necessary to inject venom into a wound. Among North American snakes the garter snakes, ring-necked snakes, cat-eyed snakes, and hog-nosed snakes are considered mildly venomous.
Some of these (e.g., the hog-nosed snakes) have specialized rear-facing fangs somewhat recessed into their throats. While most adult sober humans of average or greater intelligence would have to work at it to get a body part in harm’s way of these fangs, inebriated or otherwise mentally impaired adults and children — the latter with smaller hands, and all possessing a less predictable repertoire of inhibitions — are more at risk. In all these cases, it makes sense to avoid allowing such individuals to handle a mildly venomous snake. Furthermore, it is always wise to avoid bites from such serpents, as the bite wound may swell, become numb, and reduce mobility of the bitten limb for a period of time following the bite.
Question: How beneficial are mildly venomous snakes, vis-a-vis earth’s ecosystem?
Answer: These snakes are extremely beneficial to mankind. Many mildly venomous snakes, such as the hog-nosed, garter snakes, and nerodian water snakes, prey on frogs and toads as well as rodents. Their unusually large adrenals protect them from toad venom, which would kill a normal snake. When these snakes are removed from a particular ecosystem, the populations of frogs and toads within that ecosystem soars. There is only one reason we almost never see six pound toads in North America; our hog-nosed, and garter snakes (along with several species of nerodian water snakes, which are considered non-venomous) are (in general, silently and because they are usually nocturnal, invisibly) doing their job of keeping the toad populations in check.
NON-VENOMOUS (and, by definition NON-DANGEROUS): A few of our North American snakes have neither fangs nor toxic salivas that are considered even remotely venomous. In between those few, and the venomous or mildly venomous snakes described above, we find a larger number whose saliva is, on careful analysis, technically active but — for practical purposes — essentially benign. Not one of these North American snakes is generally recognized as having a saliva that is harmful to humans. Interestingly, anticoagulants in the salivas of some “non-venomous” snakes — which help the snake digest its prey by keeping its fluids flowing — will cause a bite wound from that snake to bleed more freely than would otherwise be the case. The effect is more beneficial than harmful, in that the free-flowing blood helps cleanse the bite wound.
Keep in mind that a “non-venomous: non-dangerous” snake is not the same as an “inoffensive” or “harmless” snake. All of our large-bodied non-venomous snakes have numerous small teeth capable of producing serious, painful wounds, especially in larger specimens, and this is particularly true of those among the latter that are possessed of pugnacious personalities. It is always wise to handle larger non-venomous snakes with thick leather gauntlet-style gloves (for example, heavy-duty leather welder’s gloves with gauntlet sleeves and kevlar linings, which are relatively inexpensive and available through most welder’s supply outlets) that protect not only the hand but the forearm as well.
HARMLESS/INOFFENSIVE (and, of course NON-DANGEROUS): It may be a stretch to classify a snake as both harmless and inoffensive. Even a snake with a mild disposition is usually capable of evacuating the contents of its cloaca (i.e., the feces, in its anal reservoir), and squirming about to smear the smelly goo over its handler’s skin, when (im)properly aroused. With this designation we take the liberty of describing all those snakes that are bereft of both toxic salivas and large teeth in muscular jaws capable of producing serious wounds as harmless/inoffensive. This class of snake does not include any of our large-bodied snakes with attitudes.
Now, Let us Proceed Onward to North American Snake Markings and Colorations:
1. Unicolor, Unmarked, or Unpatterned: A single color to the scales, and usually the interstitial spaces between the scales, over the spine, and on the sides of the snake, without any obvious markings; many unpatterned snakes have a single color to the scales and belly, or a paler or slightly different coloration to the interstitial spaces between the scales, and to the belly as well.
Many of our smaller snakes (speaking of adults, not juveniles) are unmarked. If you see a small, unmarked brown or gray snake with a small head in your garden, it is likely one of our non-venomous adult garden snakes. Note, however, that an all-black snake with a small head (little or no neck separating the head from the rest of the body) may be a melanistic Texas coral snake, which is venomous and dangerous.
Large, darkly colored, unmarked or poorly marked snakes are difficult to identify from markings and coloration alone. Many species, both venomous and non-venomous, tend to darken with age and lose the patterns of their youth and middle age. Should you meet such a snake in your garden or on the trail, you will need to observe its head and tail to identify its species.
2. Spinal Diamond: Relatively large square, rectangular, diamond-shaped, oval, or saddle-shaped markings, occupying more than eight dorsal scales (a distinction pointed out by Werler & Dixon, in their book “Texas Snakes”), running in a single row down the snake’s spine.
The word “diamond” is used, by convention, almost exclusively to refer to the sometimes indistinct, often un-diamond-like markings along the spines of the western and eastern diamond-backed rattlesnakes (Crotalus adamanteus and C. atrox,) found throughout the eastern and western halves of North America, respectively, and the red diamond rattlesnake (Crotalus ruber), found in southern California. The photo at the head of this page is of the spinal markings of the western diamond-backed rattlesnake (Crotalus atrox), but there are no significant visible differences between C. atrox and C. adamanteus, and the same basic pattern obtains with C. ruber, though with a more typically reddish hue. One might opine that this pattern, in all three species, is not at all like that of a diamond, inasmuch as diamonds have sharp, distinct edges, while this mark is edged in a way that actually looks blurred. But look closer. The edge of each mark is made up of a series of triangular marks–which range from dark gray to bright white–that, considered separately–are quite diamond-like. It is this quality, in combination with the overall marking itself, that lends credence to the descriptor.
The caveat ”in combination with the overall marking itself ” is advised, because three other, non-venomous snakes have similar, small, circular (speckled racer & speckled king snake) or diamond-shaped (buttermilk racer) marks scattered over their bodies, but they do not form the edge of a composite diamond-shaped mark like the one found on the spines of the diamond-backed rattlers. Another non-venomous snake, the desert king snake (a subspecies of the speckled king snake), has a series of yellow-to-white speckles on a dark black background, arranged so as to outline a series of black blotches down its spine; this latter pattern has been described to me as “diamond-shaped” by some observers.
But, so much for language exclusivities. It happens that several venomous rattlesnakes found in North America, though not identified by their common names as having diamond-shaped markings, appear very much like the diamond-backed and diamond rattlesnakes mentioned above. These include the northern black-tailed rattlesnake (Crotalus molossus molossus), and the Mojave rattlesnake (Crotalus scutulatus scutulatus), both of whose diamond-shaped markings are narrowed longitudinally and broadened laterally.
One other North American snake is described as “diamond-backed” in its common name: the non-venomous diamond-backed water snake (Nerodia rhombifer rhombifer). In this snake, the “diamonds” along its spine are formed by diagonal crossbars that intersect at the spine to form a series of “X” marks joined together, head to tail. It is not likely that this species will be mistaken for a diamond-backed rattlesnake, though because it is so aggressive, and actively defends its territory when disturbed, it is often misidentified as a venomous western cottonmouth.
Many other snakes, venomous and non-venomous alike, have what reasonable observers might report as ”diamond-like” markings along their spines, but because they do not have the composite features of the diamond-backed rattlesnakes, or the rhomboidal lines of the diamond-backed water snake, they are termed “saddles” or “blotches”. Thus, it is important to be familiar with the individual markings of each species, without relying on the crude conventions of language, in order recognize one species from another. Once you become familiar with the markings of a western or eastern diamond-backed rattlesnake, the red diamond rattlesnake, the northern black-tailed rattlesnake, or the Mojave rattlesnake, it is much less likely that you might mistake them for any of our non-venomous snakes.
3. Spinal Blotch or Saddle: A large oval, rectangular, square, saddle-shaped, saddle-blanket-shaped, or diamond-shaped, marking, spaced repeatedly down the snake’s spine.
4. Lateral Blotch: A relatively large square, rectangular, diamond-shaped, or oval marking, generally occupying more than eight dorsal scales, running in one or several rows longitudinally along the snake’s side (vs. “saddle shaped” markings, which is only descriptive of markings that occur along a snake’s spine).
Large markings on the sides of a snake are as useful as indicators of the snake’s identity as those along the snake’s spine. For many non-venomous snakes, such as the Texas rat snake, the bull snake, the Texas glossy snake, and certain species of garter snake, the lateral blotches may be the first thing you notice.
5. Spot or Speck: Not as large as a blotch (i.e., occupying less than eight dorsal scales); may occupy as few as a single dorsal scale, or only a portion of such a scale.
6. Band or Ring: A band or ring of coloration that completely encircles the snake’s body.
Note that whether or not a band or ring completely encircles tha snake’s body won’t be immediately clear when the snake is encountered in the wild. Thus it helps to become familiar with the markings of the various snake species before you encounter them.
7. Crossband, Half-ring, Chevron, or Bar: A band or ring of coloration that passes laterally across the snake’s spine onto the snake’s sides, without fully crossing the snake’s belly.
Some crossbands, half-rings, and bars, on the back and sides of certain snake speceis clearly terminate before ethey reach the lower regions of the snake’s sides. Others extend all the way to the belly, and some encroach onto the belly itself before they are interrupted.
8. Spinal Stripe: A longitudinally oriented stripe or strip of coloration along the snake’s spine, often extending from the head to the tail.
9. Lateral Stripe: A longitudinally-oriented stripe or strip of coloration along the snake’s side (vs. along the snake’s spine), often extending from head to tail.
10. Hour-glass: A marking that is broad at its origin near the belly, that first broadens slightly, then narrows as it approches the spine; such markings are found only on certain species of copperheads and the western cottonmouth.
Above photo: Unicolor, Unmarked, or Unpatterned. Western earth snake (Virginia valeriae elegans) adult, midbody; distinguished from the rough earth snake (Virginia striatula) by the latter’s cone-shaped head and keeled scales. HARMLESS/INOFFENSIVE.
Above photo: Unicolor, Unmarked, or Unpatterned. Rough green snake (Opheodrys aestivus) adult, midbody. There are no unmarked blue snakes native to North America, but you may find a dead snake that is both unmarked and blue. If you find such a snake, it is almost certainly one of our unmarked green snakes, such as this one, all of whom turn blue at death. HARMLESS/INOFFENSIVE.
Above photo: Diamonds. Diamond-backed water snake (Nerodia rhombifer rhombifer). With this species, the “diamonds” appear much like X marks down the snake’s spine. In the featured specimen, the X markings are not quite as clear as in the “typical” snake of this species, but they can still be seen. NON-VENOMOUS.
Above photo: Diamonds. Diamond-backed water snake (Nerodia rhombifer rhombifer). These X marks down the snake’s spine are a bit easier to see. Note that the midpoint of each X is an enlarged squarish mark. This is not an unusual variation. NON-VENOMOUS.
Above photo: Diamonds. Diamond-backed water snake (Nerodia rhombifer rhombifer). The X marks on this snake’s spine don’t connect to the lateral crossbars, which is atypical for the species. However, the lateral crossbars mark the snake as a Nerodian, especially in the presence of the spinal blotches, and the bright coloration of the spaces between each lateral crossbar is characteristic of the diamond-backed water snake and few others. The Louisiana pine snake has similar lateral crossbars, but they are rarely as consistent as these. NON-VENOMOUS.
Above photo: Diamonds. Western diamond-backed rattlesnake (Crotalus atrox). The pattern of the diamonds indicates where the head and tail are located. The lighter colored small diamonds line the trailing edges of the large composite diamond marking, and sweep backward as though blown by the wind, pointing toward the tail. The forward edges of the large composite diamond markings are blunt, as though buffeted by the wind, and point toward the head. VENOMOUS.
Above photo: Diamonds. Western diamond-backed rattlesnake (Crotalus atrox). If you peered into a section of pine flooring, and this is all you saw of the snake, which way (left or right) would you expect to find the head? VENOMOUS.
Above photo: Spinal Saddles with Lateral Blotches. Texas ratsnake (Elaphe obsoleta lindheimeri). Notice how the lateral blotches, surrounded as they are by the snake’s lighter background coloration, and by the spinal saddles, create the appearance of a chain-link fence. This effect is very pronounced in many Texas rat snakes. NON-VENOMOUS.
Above photo: Spinal Saddles with Lateral Blotches. Texas ratsnake (Elaphe obsoleta lindheimeri). Notice, again, how the lateral blotches are clearly separated from the spinal saddles by the snake’s lighter background coloration, creating the appearance of a chain-link fence. When you see this effect, think “Texas ratsnake,” and remember how beneficial these snakes are to your ecosystem, not only because they prey on rodents, but because their rodent predation is so effective that it significantly reduces prey for venomous snakes, leading them to relocate to areas where ratsnakes are less plentiful. NON-VENOMOUS.
Above photo: Spinal Saddles with Lateral Blotches. Yet another Texas ratsnake (Elaphe obsoleta lindheimeri). Notice, again, how the lateral blotches are clearly separated from the spinal saddles by the snake’s lighter background coloration. This is an older snake, whose markings are darkening. Eventually these snakes become so dark that the markings are difficult to make out. However, we rarely see rat snakes that old these days, as most meet their demise at the business end of a hoe or a shovel wielded by individuals who are not aware how beneficial these snakes are. NON-VENOMOUS.
Above photo: Spinal Saddles with Lateral Blotches. Another Texas ratsnake (Elaphe obsoleta lindheimeri). Notice, however, that the lateral blotches, while separated from the spinal saddles by the snake’s lighter background coloration, are not as regular as in the other Texas rat snake specimens, above. In some respects, these markings look more like those of the bull snake or Louisiana pine snake, but an examination of the head (not visible in this photo section) confirms that it is a Texas rat. This points out that, in many cases, a snake cannot be positively identified by viewing the midbody markings alone. NON-VENOMOUS.
More to come!!! This article is a work in progress.
Related Links on BugsInTheNews:
- North American Snake Markings & Coloration Guide.
- Ophidian Dentition — Snake Teeth & Fangs — Morphology & Specialization
- Snake Anatomy, Physiology, and Taxonomy.
- Snake Exclusion — How to Snake-proof your Yard and Home.
- Snake Repellents — How, and How Well, do They Work?
- Snakebite First Aid.
- Snakes, Rodents, & Droughts.
- What is Meant by “A Reasonably Snake-Free Environment”?
- Texas Coral Snake (Micrurus fulvius tener); John H., Dripping Springs, Texas — 01 May 2010
- Western Cottonmouth (Agkistrodon piscivorus leucostoma, Troost 1836) juvenile snakebite; Margaret Archer, Manvel, TX — 5 Sep 2011
- Cottonmouths & Copperheads in Travis and Harris Counties, Texas — June to August, 2010
- Western Cottonmouth (Agkistrodon piscivorus leucostoma, Troost 1836); Tammy D., Santa Fe, TX — 28 Aug 2011
- Western Diamond-backed Rattlesnake (Crotalus atrox, Baird & Girard, 1853), Cedar Creek, TX — 22 Oct 2010.
References to Scientific Articles, Books, and Papers:
- Arikan, Hüseyin et al. 2008. Electrophoretic characterisation of the venom samples obtained from various Anatolian snakes(Serpentes: Colubridae, Viperidae, Elapidae). N.W. J. Zool. Vol. 4, No. 1, pp.16-28.
- Birchard, Geoffrey F., et al., 1984. Foetal-Maternal Blood Respiratory Properties of an Ovoviviparous Snake; the Cottonmouth, Agkistrodon piscivorus. J. exp. Biol. 108, 247-25
- Brodie, E. D. III, and F. J. Janzen. Experimental Studies of Snake Mimicry; Generalized Avoidance of Ringed Snakes Patterns by Free-ranging Avian Predators. Functional Ecology Vol. 9, No. 2 (186-190).
- Chao, Betty H., et al. 1989. Agkistrodon piscivorus piscivorus platelet aggregation inhibitor: A potent inhibitor of platelet activation.Proc. Natl. Acad. Sci. USA Vol. 86, pp. 8050-8054
- Chippaux, J. P., et al. 1991. Snake Venom Variability: Methods of study, results, and Interpretation. Toxicon Vol. 29, No. I I , pp. 1279-1303.
- Coborn, John. 1995.Boas & Pythons and Other Friendly Snakes. T. F. H. Publications Inc.
- Conant, Roger, and Joseph T. Collins, 1998. Reptiles and Amphibians — Eastern/Central North America, Third Ed. Peterson Field Guides. Houghton Mifflin Co.
- Cundall, David. 2009. Viper Fangs: Functional Limitations of Extreme Teeth. Physiological and Biochemical Zoology 82(1):63–79.
- Deufel, Alexandra, and David Cundall. 2004.Functional plasticity of the venom delivery system in snakes with a focus on the poststrike prey release behavior. Zoologischer Anzeiger 245 (2006) 249–267.
- Eckerman, Curtis M. 1997. Allopatric Mimicry. Unpublished Graduate Research Report prepared for the journal Evolutionary Ecology.
- Grachevca, Elena, et al., 2010. Molecular Basis for Infrared Detection by Snakes. Nature, 15 April 2010.
- Greene, Harry W., 1997. Snakes: the Evolution of Mystery in Nature. University of California Press.
- Greene, Harry W., and Roy W. McDiarmid. 2005. Wallace and Savage: Heroes, Theories, and Venomous Snake Mimicry. Ch. 9 of Ecology and evolution in the tropics: a herpetological perspective. Univ. Chicago Press.
- Johnson, Tom R. 2000. Missouri Copperheads. Missouri Conservation Commission.
- Klauber, Lawrence M. 1982. Rattlesnakes: their Habits, Life Histories & Influence on Mankind. Univ. Calif. Press.
- Rodrıguez-Robles, Javier A., and Jose´ M. De Jesus-Escobar. 2000. Molecular Systematics of NewWorld Gopher, Bull, and Pinesnakes(Pituophis: Colubridae), a Transcontinental Species Complex. Molecular Phylogenetics and Evolution, Vol. 14, No. 1, January, pp. 35–50.
- Schulz, Klaus-Dieter, 1996. A Monograph of the Colubrid Snakes of the Genus Elaphe Fitzinger. Koeltz Scientific Books.
- Tennant, Alan,1998. A Field Guide to Texas Snakes, Second Ed. Gulf Publishing.
- Weinstein, Scott A., et al. 1994.Reptile Venom Glands — Form, Function, and Future. Handbook of Venoms and Toxins of Reptiles. CRC Press.
- Werler, John E., and James R. Dixon, 2000. Texas Snakes. University of Texas Press.
- World Health Organization. 2002. Management of Snakebite and Research. WHO SEA-RES-2.
- Wozniak, Edward J., John Wisser, and Michael Schwartz. 2006. Venomous Adversaries: A Reference to Snake Identification, Field Safety, and Bite-Victim First Aid for Disaster-Response Personnel Deploying Into the Hurricane-Prone Regions of North America. Wilderness and Environmental Medicine, 17, 246-266.
- Zaidan, Frederick III, 2002. Variation in cottonmouth (Agkistrodon piscivorus leucostoma) resting metabolic rates. Comparative Biochemistry and Physiology Part A 134 (2003) 511–523
- Zamudio, Kelly R., et al., 2000. Fang tip spread, puncture distance, and suction for snake bite. Toxicon 38 (2000) 723 – 728
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