Madison Area Herpetological Society

Shedding the Uncertainty: How to Identify Snake Sheds

Shedding the Uncertainty: How to Identify Snake Sheds
By Eric Roscoe

One very commonly seen and asked question and topic that recently has been asked with greater frequency both online through Facebook, social media, and other forums, as well as in person, is identifying snakes based on their shed, or sheddings being found or left behind. Oftentimes, a photo may be taken or included, and the question and/or concern of whether the snake is venomous or nonvenomous is also very frequently asked. While it can often be difficult to determine a species from an imprecise photo lacking details and/or without a precise location given (such as the state and region the shed was found in), it can also oftentimes be possible to accurately identify a shedding if these details (to be briefly discussed and highlighted below) are included in the description and/or photos of any given shedding ID inquiry. Many snakes in adequate health will shed their skins in a single, or several large pieces, making identification of their sheds more possible. It can be much more difficult to accurately ID or pinpoint the species if only fragments of a shed are available, although it may still be easy or possible in some cases depending on the species. Sheds from snakes can also be fragile, and easily torn by the wind, other animals, or other natural elements, etc and will often become more brittle over time vs. a freshly deposited shed that is still soft or wet.

The article will focus only on shedding inquiries for native, or indigenous snake species in North America, as these tend to be the most commonly encountered and likely candidates for the vast majority of such IDs in the U.S. and Canada. If there is a shedding found that still is unfamiliar, or cannot be keyed out using any of the information below, the Madison Area Herpetological Society is always more than glad to assist in further identifying or keying out the shed to the best of our ability and information given. With this stated, there are two main scientific families of snakes found in most areas of North America and Canada; Colubridae (which include the vast majority of harmless and/or nonvenomous North American snakes), and the Crotalinidae (which include the heavier bodied species of pit vipers including rattlesnakes, copperheads, and cottonmouths). Other minor families found in some areas of North America include the Boidae (two species, found in the southwestern to northwestern United States and southwestern Canada), and the Elapidae (primarily the venomous coral snakes).

General/Overall Shedding
Examining the overall shedding can oftentimes provide some additional clues or information into the species of snake that left it. Take note of the overall size of the shedding, as this can oftentimes rule out small species, although this will not account for possible young or juvenile snakes of the same large species. Also take note of the girth of the shed, as some species of snakes are heavier or shorter bodied than others, which may be relatively longer and slender. North America does not have any indigenous species of venomous snakes that are long and slender, so it can be immediately known that a shed fitting this description will be from a nonvenomous snake, for example. In addition, although sheddings will stretch and expand somewhat in length and girth to be slightly larger and longer than the actual animal that shed them, the relative proportions still remain similar and can oftentimes provide an idea into the snake in question. In the case of rattlesnake sheddings (Crotalus sp. And Sistrurus sp.), the presence of a rattle is usually lacking unless segments are also left behind. A rattlesnake’s rattle is comprised of keratin (the same material as human hair and fingernails), and is also fragile and can be easily broken or damaged. Most neonate and juvenile rattlesnakes begin life with a single rattle segment known as a “button”, and new or multiple segments are added each time the snake grows and sheds. Depending on food availability and other resources and environmental conditions, a rattlesnake may shed up to several times each year, and therefore counting the number of segments is not an accurate method of determining the age of a rattlesnake.
Patterning can also often be preserved in a shed, particularly if it is of high contrast although coloration will obviously be absent. Banding, stripes, spots, blotches, solid uniform coloration, or other forms of patterning may be evident and provide insight into identification of a shed, but even then will become obscured or fade indiscernibly over time once the shedding dries out or becomes brittle. Good lighting and proper angles or perspectives may also be required to discern any patterns in a shedding.

Dorsal Scales
The dorsal scales comprise the vast majority of scales covering the snake’s body along its back and sides that are not otherwise ventral scales. Both the dorsal and ventral scales serve as protection for the snake from potential predators, as well as preventing desiccation (retaining moisture and hydration), and assisting in the snake’s overall movements and locomotion. Many snakes can be identified or keyed out on basis such as whether scalation is keeled, semi or weakly keeled, or smooth. Keels are tiny prism like ridges present on each dorsal scale, or the top most dorsal scales depending on the species, that give the snake a rougher textured feel than a species that has smooth scales. With the exception of the North American coral snakes, all North American venomous snakes are otherwise pit vipers that have keeled to weakly keeled scales, although whether dorsal scales are keeled or smooth in of itself is not diagnostic in identifying a snake or its shed as a venomous species (See anal and sub caudal scalation section below).

Head Scales
Much like its dorsal and ventral scales, a snake’s head and facial scalation serves as additional protection and prevention from external elements and desiccation, as well as providing the head (which is the most vulnerable portion of the snake’s body where the animal’s brain and central nervous system are  located) additional protection from potential predation. Different specific scales located on different areas or regions of the head also bear their own terms or definitions. For example, the largest, plate like scales on the posterior most area atop the head are called the parietal scales. The supraocular scales are the scales located directly above the eyes, and may appear as specially modified horn or ridge like projections in some specialized species. The frontal scale is the large scale or scales between the supraocular scales atop the head, while the rostral scale is the scale covering the tip of the snout (and which may also be specifically upturned or modified in some species for specialized lifestyles, such as hognose snakes or the genus Heterodon). The supra and infra labial scales are the row of scales lining the upper and lower lips and jaws, and may have specialized heat pits in some families of snakes (such as boas and pythons), although these pits are not obvious on sheds. Members of the pit viper families also have specialized heat pits located on the loreal scales (located between the eyes and nostrils/tip of the snout), although these tend not to be obvious on sheds as well. The post ocular scales are the scales directly behind the eyes and at an angle, and which are often covered in a dark stripe or post ocular band on sheds that can readily be seen on some species. Finally, there is the spectacle, or eye caps themselves, with are clear, transparent scales covering the eyes for protection from the external elements. Different species and genra have different sizes, numbers, and/or arrangements of all of these forms of head scalation, making this method of identification a standard practice in identifying both snakes and their sheddings.

Anal and Sub caudal Scales
The anal, or ventral scale is the protective scale covering the snake’s vent and cloaca, which serves as an all-purpose opening for dispensing wastes as well as reproduction. It also indicates the beginning of the snake’s tail, which is followed ventrally by what are known as the sub caudal scales. Depending on the species, the anal scale may be single and undivided, partially divided, or fully divided. The subcaudal scales are also nearly an invariable method of identifying or distinguishing most North American snakes as venomous or nonvenomous. With the exception of the North American coral snakes (Micrurus sp.), as well as the North American boa species, all venomous species in North America are otherwise pit vipers that have a single anal scale AND single row of sub caudal scales present. Likewise, the vast majority of North American snakes and their sheds with a double row of sub caudal scales (not withstanding the above mentioned coral snakes and boas) are quite likely to be harmless and nonvenomous species.

 

Key to Common Species of Snake Sheds

1. Single Anal Scale

    1a. Single Sub Caudal Scale Row, Dorsal Scales Keeled or Semi Keeled, Pattern Evident or Usually Evident

    -Rattlesnake species (Crotalus sp.)*Venomous, best left alone
    -Massasauga/Pygmy Rattlesnake species (Sistrurus sp.)*Venomous, best left alone.
    -Cottonmouth/Water Moccasin (Agkistrodon                                  piscivorous)*Venomous, best left alone.
    -Copperhead (Agkistrodon contortrix)*Venomous, best left alone.

    1b. Single Sub Caudal Scale Row, Dorsal Scales Small or Granular, Pattern Evident or Usually Evident, Tail Very Blunt, Cloacal Spurs Present

    -Rubber Boa (Charina bottae)*Harmless, and Nonvenomous
    -Rosy Boa (Lichanura trivirgata)*Harmless, and Nonvenomous

1c. Double Sub Caudal Scale Row
    1c1. Keeled or Semi Keeled Dorsal Scales, Pattern Evident or Usually Evident

    -Bullsnake, Pine Snake, or Gopher Snake species (Pituophis sp.)*Harmless and Nonvenomous
    -Garter Snake or Ribbon Snake species (Thamnophis sp.)*Harmless, and Nonvenomous
    -Lined Snake (Tropidoclonion lineatum)*Harmless, and Nonvenomous

    1c2. Smooth Dorsal Scales, Pattern Evident or Usually Evident

    -Common Kingsnake species (Lampropeltis getula ssp.)*Harmless, and Nonvenomous
    -Milk Snake species (Lampropeltis triangulum ssp.)*Harmless, and Nonvenomous
    -Scarlet Snake (Cemophora sp.)*Harmless, and Nonvenomous
    -Mole and Prairie Kingsnakes (Lampropeltis calligaster)*Harmless, and Nonvenomous
    -Indigo Snakes (Drymarchon sp.)*Harmless, and Nonvenomous
    -Glossy Snakes (Arizona sp.)*Harmless, and Nonvenomous
    -Long Nosed Snakes (Rhinocheilus sp.)*Harmless, and Nonvenomous

 

2. Divided or Partially Divided Anal Scale
    2a. Double Sub Caudal Scale Row, Pattern Evident or Usually Evident

     2a1. Keeled or Semi Keeled Dorsal Scales

    -Water Snake species (Nerodia sp.)*Harmless, and Nonvenomous
    -Hognose Snake species (Heterodon sp.)*Harmless, Not a Threat to People
    -DeKay’s/Brown/Red bellied Snake species (Storeria sp.)*Harmless, and Nonvenomous
    -Rough Green Snake (Opheodrys aestivus)*Harmless, and Nonvenomous
-Corn/Red Rat Snake (Panthertophis guttata)*Harmless, and Nonvenomous
    -Fox Snake species (Panthertophis vulpinus)*Harmless, and Nonvenomous
    -North American Rat Snake species (Panthertophis sp.)*Harmless, and Nonvenomous
    -Trans Pecos/Desert Rat Snakes (Bogertophis sp.)*Harmless, and Nonvenomous
    -Crayfish and Queen Snake species (Regina sp.)*Harmless, and Nonvenomous
    -Earth Snakes (Virginia sp.)*Harmless, and Nonvenomous
    -Kirtland’s Snake (Clonophis sp.)*Harmless, and Nonvenomous

    2a2. Smooth Dorsal Scales

    -Worm Snakes (Carphophis sp.)*Harmless, and Nonvenomous
    -North American Racers, Whip Snakes, and Coachwhips (Coluber/Masticophis sp.)*Harmless, and Nonvenomous
    -Ringneck Snakes (Diadophis punctatus ssp.)*Harmless, and Nonvenomous
    -Smooth Green Snake (Opheodrys vernalis)*Harmless, and Nonvenomous
    -Mud and Rainbow Snakes (Farancia sp.)*Harmless, and Nonvenomous
    -North American Coral Snakes (Micrurus sp.)*Venomous, best left alone.
-Crowned and Black Headed Snakes (Tantilla sp.)*Harmless, and Nonvenomous
    -Shovel Nosed Snakes (Chionactis sp.)*Hamless, and Nonvenomous
-Night Snakes (Hypsiglena sp.)*Harmless, and Not Dangerous to People
    -Swamp Snakes (Seminatrix sp.)*Harmless, and Nonvenomous
    -Ground Snakes (Sonora sp.)*Harmless, and Nonvenomous
    -Pine Woods Snake (Rhadinaea sp.)*Harmless and Not Dangerous to People
    -Lyre Snakes (Trimorphodon sp.) *Harmless and Not Dangerous to People

 

Key to Species of Snake Sheds-Wisconsin Version

1. Single Anal Scale

    1a. Single Sub Caudal Scale Row, Dorsal Scales Keeled or Semi Keeled, Pattern Evident or Usually Evident

    -Timber Rattlesnake (Crotalus horridus)*Venomous, best left alone
    -Eastern Massasauga (Sistrurus catenatus)*Venomous, best left alone.

 

1b. Double Sub Caudal Scale Row
    1b1. Keeled or Semi Keeled Dorsal Scales, Pattern Evident or Usually Evident

    -Bullsnake (Pituophis catenifer sayi)*Harmless and Nonvenomous
    -Common Garter Snake (Thamnophis sirtalis ssp.)*Harmless, and Nonvenomous
-Butler’s Garter Snake (Thamnophis butleri)*Harmless, and Nonvenomous
-Plains Garter Snake (Thamnophis radix)*Harmless, and Nonvenomous
-Western/Orange Striped Ribbon Snake (Thamnophis proximus proximus)*Harmless, and Nonvenomous
-Northern/Eastern Ribbon Snake (Thamnophis sauritus septentrionalis.)*Harmless, and Nonvenomous
    -Lined Snake (Tropidoclonion lineatum)*Harmless, and Nonvenomous

    1b2. Smooth Dorsal Scales, Pattern Evident or Usually Evident

    -Eastern Milk Snake (Lampropeltis triangulum triangulum.)*Harmless, and Nonvenomous

2. Divided or Partially Divided Anal Scale
    2a. Double Sub Caudal Scale Row, Pattern Evident or Usually Evident

     2a1. Keeled or Semi Keeled Dorsal Scales

    -Northern Water Snake (Nerodia sipedon)*Harmless, and Nonvenomous
    -Eastern Hognose Snake (Heterodon platirhinos)*Harmless, Not a Threat to People
    -DeKay’s/Brown Snake (Storeria dekayi)*Harmless, and Nonvenomous
    -Red bellied Snake (Storeria occipitomaculata)*Harmless, and Nonvenomous
    -Western Fox Snake (Panthertophis vulpinus)*Harmless, and Nonvenomous
    -Midland/Gray Rat Snake (Panthertophis spiloides)*Harmless, and Nonvenomous
    -Queen Snake species (Regina septemvittata)*Harmless, and Nonvenomous

    2a2. Smooth Dorsal Scales

    -Western Worm Snake (Carphophis vermis)*Harmless, and Nonvenomous
    -North American Racers (Coluber constrictor ssp.)*Harmless, and Nonvenomous
    -Ringneck Snakes, Northern or Prairie (Diadophis punctatus ssp.)*Harmless, and Nonvenomous
    -Smooth Green Snake (Opheodrys vernalis)*Harmless, and Nonvenomous