SnakeSnakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, like other
reptileReptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, have a skin covered in
scaleIn most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s. Snakes are entirely covered with scales or scutes of various shapes and sizes. Scales protect the body of the snake, aid it in locomotion, allow moisture to be retained within, alter the surface characteristics such as roughness to aid in camouflage, and in some cases even aid in prey capture (such as Acrochordus). The simple or complex colouration patterns (which help in camouflage and anti-predator display) are a property of the underlying skin, but the folded nature of scaled skin allows bright skin to be concealed between scales then revealed in order to startle predators.
Scales have been modified over time to serve other functions such as 'eyelash' fringes, and protective covers for the eyes with the most distinctive modification being the
rattle of the North American rattlesnakes.
Snakes periodically moult their scaly skins and acquire new ones. This permits replacement of old worn out skin, disposal of parasites and is thought to allow the snake to grow. The arrangement of scales is used to identify snake species.
Snakes have been part and parcel of culture and religion. Vivid scale patterns have been thought to have influenced early art. The use of snake-skin in manufacture of purses, apparel and other articles led to large-scale killing of snakes, giving rise to advocacy for use of artificial snake-skin. Snake scales are also to be found as motifs in fiction, video games and films.
Functions of scales
The scales of a snake primarily serve to reduce friction as it moves, since friction is the major source of energy loss in
snake locomotion. The ventral (or belly) scales, which are large and oblong, are especially low-friction, and some arboreal species can use the edges to grip branches. Snake skin and scales help retain moisture in the animal's body. Snakes pick up vibrations from both the air and the ground, and can differentiate the two, using a complex system of internal resonances (perhaps involving the scales).
Morphology of scales
Snake scales are formed by the differentiation of the snake's underlying skin or
epidermis. Each scale has an outer surface and an inner surface. The skin from the inner surface hinges back and forms a free area which overlaps the base of the next scale which emerges below this scale. A snake hatches with a fixed number of scales. The scales do not increase in number as the snake matures nor do they reduce in number over time. The scales however grow larger in size and may change shape with each
moultIn biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
.
Snakes have smaller scales around the mouth and sides of the body which allow expansion so that a snake can consume prey of much larger width than itself. Snake scales are made of
keratinKeratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
, the same material that hair and fingernails are made of. They are cool and dry to touch.
Surface and shape
Snake scales are of different shapes and sizes. Snake scales may be granular, have a smooth surface or have a longitudinal ridge or keel on it. Often, snake scales have pits, tubercles and other fine structures which may be visible to the naked eye or under a microscope. Snake scales may be modified to form fringes, as in the case of the Eyelash Bush Viper,
Atheris ceratophoraAtheris ceratophora is a venomous viper species found only in a few mountain ranges in Tanzania. This is the only horned, arboreal viper in Africa. No subspecies are currently recognized.-Description:...
, or rattles as in the case of the
rattlesnakeRattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae . There are 32 known species of rattlesnake, with between 65-70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to Central...
s of
North AmericaNorth America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Certain primitive snakes such as boas, pythons and certain advanced snakes such as
viperThe Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...
s have small scales arranged irregularly on the head. Other more advanced snakes have special large symmetrical scales on the head called
shields or
plates.
Snake scales occur in variety of shapes. They may be cycloid as in family
TyphlopidaeThe Typhlopidae are a family of blind snakes. They are found mostly in the tropical regions of Africa, Asia, the Americas, and all mainland Australia and various islands. The rostral scale overhangs the mouth to form a shovel like burrowing structure. They live underground in burrows, and since...
, long and pointed with pointed tips, as in the case of the Green Vine Snake
Ahaetulla nasutaThe Green vine snake , is a slender green tree snake found in India, Sri Lanka, Bangladesh, Myanmar, Thailand, Cambodia and Vietnam.-Description:...
, broad and leaf-like, as in the case of green pit vipers
TrimeresurusTrimeresurus is a genus of venomous pitvipers found in Asia from Pakistan, through India, China, throughout Southeast Asia and the Pacific Islands. Currently 35 species are recognized...
spp or as broad as they are long, for example, as in Rat snake
Ptyas mucosusDhaman or Oriental Ratsnake Ptyas mucosus is a common species of colubrid snake found in parts of South and Southeast Asia. Growing to nearly two metres, they are large snakes and their colour varies from pale browns in dry regions to nearly black in moist forest areas...
.
In some cases, scales may be
keeledKeeled scales refer to reptile scales that, rather than being smooth, have a ridge down the center that may or may not extend to the tip of the scale, making them rough to the touch...
weakly or strongly as in the case of the Buff-striped keelback
Amphiesma stolatumThe buff striped keelback is a species of nonvenomous colubrid snake found across Asia. It is a typically nonaggressive snake that feeds on frogs and toads. It belongs to the subfamily Natricinae, and is closely related to water snakes and grass snakes. It pretty much resembles an Asian version of...
. They may have bidentate tips as in some spp of
NatrixNatrix is a genus of colubrid snakes. There are three or four species in the genus. They are collectively called grass snakes and water snakes...
. Some snakes, such as the Short Seasnake
Lapemis curtusThe Shaw's Sea Snake is a species of sea snake.Distribution:Persian Gulf Indian Ocean South China Sea north to the coasts of Fujian and Shandong...
, may have spinelike and juxtaposed scales while others may have large and non-overlapping knobs as in the case of the Javan Mudsnake
Xenodermis javanicusJavan mudsnake Xenodermis javanicus is a Colubrid snake found in South East Asia. It is noted for having large non-overlapping knobby scales of various diameters. The Javan Mudsnake has an enlarged head, heavily ridged scales separated by areas of much smaller scales, and an elongated tail. It is...
.
Another example of differentiation of snake
scalesIn most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
is a transparent scale called the
brille or
spectacle which covers the eye of the snake. The brille is often referred to as a fused eyelid. It is shed as part of the old skin during
moultIn biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
ing.
Rattles
The most distinctive modification of the snake scale is the
rattle of rattlesnakes, such as those of the genera
CrotalusCrotalus is a genus of venomous pit vipers found only in the Americas from southern Canada to northern Argentina. The name is derived from the Greek word krotalon, which means "rattle" or "castanet", and refers to the rattle on the end of the tail which makes this group so distinctive...
and
SistrurusSistrurus is a genus of venomous pit vipers found in Canada, the United States and Mexico. The name is a Latinized form of the Greek word for "tail rattler" and shares its root with the ancient Egyptian musical instrument, the sistrum, a type of rattle...
. The rattle is made up of a series of loosely linked, interlocking chambers that when shaken, vibrate against one another to create the warning signal of a rattlesnake. Only the bottom button is firmly attached to the tip of the tail.
At birth, a rattlesnake hatchling has only a small button or 'primordial rattle' which is firmly attached to the tip of the tail. The first segment is added when the hatchling sheds its skin for the first time. A new section is added each time the skin is shed until a rattle is formed. The rattle grows as the snake ages but segments are also prone to breaking off and hence the length of a rattle is not a reliable indicator of the age of a snake.
Colour
Scales, more specifically, mostly consist of hard beta
keratinKeratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
s which are basically transparent. The colours of the scale are due to pigments in the inner layers of the skin and not due to the scale material itself. Scales are hued for all colours in this manner except for blue and green. Blue is caused by the
ultrastructureUltrastructure is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be observed by electron microscopy...
of the scales. By itself, such a scale surface diffracts light and gives a blue hue, while, in combination with yellow from the inner skin it gives a beautiful iridescent green.
Some snakes have the ability to change the hue of their scales slowly. This is typically seen in cases where the snake becomes lighter or darker with change in season. In some cases, this change may take place between day and night.
Ecdysis
The shedding of scales is called
ecdysisEcdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
, or, in normal usage
moultIn biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
ing or
sloughing. In the case of snakes, the complete outer layer of skin is shed in one layer. Snake scales are not discrete but extensions of the epidermis hence they are not shed separately, but are ejected as a complete contiguous outer layer of skin during each
moultIn biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
, akin to a sock being turned inside out.
MoultIn biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
ing serves a number of functions - firstly, the old and worn skin is replaced, secondly, it helps get rid of parasites such as mites and ticks. Renewal of the skin by
moultIn biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
ing is supposed to allow growth in some animals such as insects, however this view has been disputed in the case of snakes.
Moulting is repeated periodically throughout a snake's life. Before a moult, the snake stops eating and often hides or moves to a safe place. Just before shedding, the skin becomes dull and dry looking and the eyes become cloudy or blue-colored. The inner surface of the old outer skin liquefies. This causes the old outer skin to separate from the new inner skin. After a few days, the eyes clear and the snake "crawls" out of its old skin. The old skin breaks near the mouth and the snake wriggles out aided by rubbing against rough surfaces. In many cases the cast skin peels backward over the body from head to tail, in one piece like an old sock. A new, larger, and brighter layer of skin has formed underneath.
An older snake may shed its skin only once or twice a year, but a younger, still-growing snake, may shed up to four times a year. The discarded skin gives a perfect imprint of the scale pattern and it is usually possible to identify the snake if this discard is reasonably complete and intact.
Arrangement of scales
Scale arrangements are important, not only for taxonomic utility, but also for forensic reasons and conservation of snake species.
Excepting for the head, snakes have imbricate scales, overlapping like the tiles on a roof. Snakes have rows of scales along the whole or part of their length and also many other specialised scales, either singly or in pairs, occurring on the head and other regions of the body.
The dorsal (or body) scales on the snake's body are arranged in rows along the length of their bodies. Adjacent rows are diagonally offset from each other. Most snakes have an odd number of rows across the body though certain species have an even number of rows e.g.
ZaocysZaocys is a genus of snakes of the family Colubridae.They reside in Singapore, Malaysia, and Thailand....
spp. In the case of some aquatic and marine snakes, the scales are granular and the rows cannot be counted.
The number of rows range from ten in Tiger Ratsnake
Spilotes pullatusSpilotes pullatus, also known as the Tigre, is a large snake found in southern Central America, northern South America and Trinidad and Tobago. It is a non-venomous colubrid that tends to inhabit forested areas. It is arboreal in habit and feeds on a wide variety of prey, including small mammals,...
; thirteen in
DryocalamusDryocalamus is a genus of colubrid snakes.Species under this genus include :* Dryocalamus nympha* Dryocalamus gracilis...
,
LiopeltisLiopeltis is a genus of colubrid snakes. Six species are known from India....
,
CalamariaCalamaria is a large genus of dwarf snakes of the family Colubridae. It contains sixty recognized species.-Description:Species in the genus Calamaria share the following characteristics. Maxillary teeth 8-11, subequal; anterior mandibular teeth a little longer than the posterior...
and Asian coral snakes of genus
CalliophisCalliophis is a genus of venomous elapid snakes known commonly as oriental coral snakes or Asian coral snakes.Species in this genus are:* Calliophis beddomei M.A. Smith, 1943– Beddome's Coral Snake...
; 65 to 75 in pythons; 74 to 93 in
KolpophisKolpophis is a genus of sea snakes of the family Hydrophiidae....
and 130 to 150 in
Acrochordus. The majority of the largest family of snakes, the
Colubridae have 15, 17 or 19 rows of scales. The maximum number of rows are in mid-body and they reduce in count towards the head and on the tail.
Nomenclature of scales
The various scales on a snake's head and body are indicated in the following paragraphs with annotated photographs of Buff-striped Keelback
Amphiesma stolata, a common grass-snake of South Asia and a member of Colubridae, the largest snake family.
Head scales
Identification of cephalic scales is most conveniently begun with reference to the nostril which is easily identified on the snake. There are two scales enclosing the nostril which are called the
nasals. In colubrids, the nostril lies between the nasals while in vipers it lies in the centre of a single nasal scale. The outer nasal (near the snout) is called the
prenasal while the inner nasal (near the eye) is called the
postnasal. Along the top of the snout connecting the nasals on both sides of the head are scales called
internasals. Between the two prenasals is a scale at the tip of the snout called the
rostral scale.
The scales around the eye are called
circumorbital scales and are named as 'ocular' scales but with appropriate prefix. The
ocular scale proper is a transparent scale covering the eye which is called the
spectacle,
brilleThe brille is the layer of transparent, immovable disc-shaped skin or scale covering the eyes of some animals for protection, especially in animals without eyelids. The brille has evolved from a fusion of the upper and lower eyelids...
or
eyecap. The circumorbital scales towards the snout or the front are called
preocular scales, those towards the rear are called
postocular scales and those towards the upper or dorsal side are called as
supraocular scales. Circumorbital scales towards the ventral or lower side, if any, are called as
subocular scales. Between the preocular and the postnasal scales are one or two scales called as
loreal scales. Loreal scales are absent in elapids.
The scales along the lips of the snake are called as
labials. Those on the upper lip are called
supralabials while those on the lower labial are called
infralabials. Between the eyeballs on top of the head, adjacent to the supraoculars are the
frontal scales. The
prefrontal scales are the scales connected to the frontals towards the tip of the snout which are in contact with the internasals. They may have a scale in between them. The back of the top of the head has scales connected to the frontal scales called as the
parietal scales. At the sides of the back of the head between the parietals above and the supralabials below are scales called
temporal scales.
On the underside of the head, a snake has an anterior scale called as the
mental scale. Connected to the mental scales and all along the lower jaws are the
infralabials. Along the lower jaw connected to infralabials are a pair of shields called the
anterior chin shields. Next to the anterior chin shields, further back along the jaw are another pair of shields called the
posterior chin shields. In some texts the chinshields are referred to as
submaxillary scales.
Scales in the central or
throat region, which are in contact with the first
ventral scalesIn snakes, the ventral scales are the enlarged and transversely elongated scales that extend down the underside of the body from the neck to the anal scale. When counting them, the first is the anteriormost ventral scale that contacts the paraventral row of dorsal scales on either side...
of a snake's body and are flanked by the
chin shieldsChin shields on a snake are scales found on the underside of the snake's head towards the anterior and touching the lower labial scales.Chin shields to the front of the snake are called anterior chin shields while those to the rear of the snake are called posterior chin shields....
, are called
gular scales. The
mental groove is a longitudinal groove on the underside of the head between large, paired chin shields and smaller gular scales.
Body scales
The scales on the body of the snake are called the
dorsal or
costal scales. Sometimes there is a special row of large scales along the top of the back of the snake, i.e., the uppermost row, called the
vertebral scales. The enlarged scales on the belly of the snake are called
ventral scales or
gastrosteges. The number of ventral scales can be a guide to the species. In "advanced" (Caenophidian) snakes, the broad belly scales and rows of dorsal scales correspond to the vertebrae, allowing scientists to count the vertebrae without dissection.
Tail scales
At the end of the ventral scales of the snake is an anal plate which protects the opening to the cloaca (a shared opening for waste and reproductive material to pass) on the underside near the tail. This
anal scale may be single or divided into a pair. The part of the body beyond the anal scale is considered to be the tail.
Sometimes snakes have enlarged scales, either single or paired, under the tail; these are called
subcaudals or
urosteges. These subcaudals may be smooth or keeled as in
Bitis arietans somalicaBitis arietans somalica, sometimes known as the Somali puff adder, is a venomous viper subspecies found only in Somalia, eastern Ethiopia and northern Kenya.-Description:Distinguished from other B. arietans by its keeled subcaudals....
. The end of the tail may simply taper into a tip (as in the case of most snakes), it may form a spine (as in
AcanthophisAcanthophis is a genus of elapid snakes. Commonly called death adders, they are native to Australia, New Guinea and nearby islands, and are among the most venomous snakes in the world...
), end in a bony spur (as in
LachesisLachesis is a genus of venomous pitvipers found in remote forested areas of Central and South America. The generic name refers to one of the Three Fates in Greek mythology who determined the length of the thread of life...
), a rattle (as in
CrotalusCrotalus is a genus of venomous pit vipers found only in the Americas from southern Canada to northern Argentina. The name is derived from the Greek word krotalon, which means "rattle" or "castanet", and refers to the rattle on the end of the tail which makes this group so distinctive...
), or a rudder as seen in many sea snakes.
Sources. Details for this section have been sourced from scale diagrams in Malcolm Smith. Details of scales of Buff-striped Keelback have been taken from Daniels.
Glossary of scales
- Scales on the head.
- Rostral.
- Nasorostral
In reptiles, the nasorostral is an enlarged and usually paired scale, just behind the rostral ....
.
- Nasal.
- Prenasal.
- Postnasal.
- Supranasal.
- Fronto-nasal.
- Internasal
In snakes, the internasal scales are those on top of the head between the scales that surround the nostrils. They are usually paired and situated just behind the rostral....
.
- Brille
The brille is the layer of transparent, immovable disc-shaped skin or scale covering the eyes of some animals for protection, especially in animals without eyelids. The brille has evolved from a fusion of the upper and lower eyelids...
, spectacle, ocular scale, eyecap.
- Circumorbital
In scaled reptiles, the ocular scales are those forming the margin of the eye. The name originates from the term oculus which is Latin for "eye" and, in the broadest sense, refers to a scale associated with the eye...
.
- Preocular
In scaled reptiles, the ocular scales are those forming the margin of the eye. The name originates from the term oculus which is Latin for "eye" and, in the broadest sense, refers to a scale associated with the eye...
.
- Postocular
In scaled reptiles, the ocular scales are those forming the margin of the eye. The name originates from the term oculus which is Latin for "eye" and, in the broadest sense, refers to a scale associated with the eye...
.
- Supraocular
In scaled reptiles, the ocular scales are those forming the margin of the eye. The name originates from the term oculus which is Latin for "eye" and, in the broadest sense, refers to a scale associated with the eye...
.
- Subocular
In scaled reptiles, the ocular scales are those forming the margin of the eye. The name originates from the term oculus which is Latin for "eye" and, in the broadest sense, refers to a scale associated with the eye...
.
- Loreal.
- Interorbital
In snakes, the interorbital scales, or intersupraoculars, are the scales on the top of the head between the plates surmounting the eyes ....
, Intersupraocular.
- Frontal.
- Prefrontal
The prefrontal scales on snakes and other reptiles are the scales connected to the frontals towards the tip of the snout which are in contact with the internasals....
.
- Parietal.
- Occipital
In reptiles, occipital scales are enlarged plates that lie directly behind the parietal scales.An interoccipital is a scale located between the occipital scales....
.
- Interoccipital
In reptiles, occipital scales are enlarged plates that lie directly behind the parietal scales.An interoccipital is a scale located between the occipital scales....
.
- Temporal
In reptiles, the temporal scales are those scales on the side of the head between the parietal scales and the supralabial scales, and behind the postocular scales.There are two types of temporal scales:...
.
- Labial.
- Supralabial
In reptiles, the supralabial scales, also called upper-labials, are those scales that border the mouth opening along the upper jaw. They do not include the median scale . The term labial originates from Labium , which refers to any lip-like structure...
, Upper labial.
- Sublabial
In reptiles, the sublabial scales, also called lower-labials or infralabials, are those scales that border the mouth opening along the lower jaw. They do not include the median scale . The term labial originates from Labium , which refers to any lip-like structure...
, Infralabial, Lower labial.
- Mental or Symphysial.
- Chin shield
Chin shields on a snake are scales found on the underside of the snake's head towards the anterior and touching the lower labial scales.Chin shields to the front of the snake are called anterior chin shields while those to the rear of the snake are called posterior chin shields....
.
- Anterior chin shield
Chin shields on a snake are scales found on the underside of the snake's head towards the anterior and touching the lower labial scales.Chin shields to the front of the snake are called anterior chin shields while those to the rear of the snake are called posterior chin shields....
, Anterior genials.
- Posterior chin shield
Chin shields on a snake are scales found on the underside of the snake's head towards the anterior and touching the lower labial scales.Chin shields to the front of the snake are called anterior chin shields while those to the rear of the snake are called posterior chin shields....
, Posterior genials.
- Intergeneial
Chin shields on a snake are scales found on the underside of the snake's head towards the anterior and touching the lower labial scales.Chin shields to the front of the snake are called anterior chin shields while those to the rear of the snake are called posterior chin shields....
.
- Gular
Gular scales on a snake are scales on the underside of a snake's head which are to be found in the central or throat region. These are in contact with the first ventral scales of a snake's body and are flanked by the chin shields.-See also:...
.
- Scales on the body.
- Dorsal
In snakes, the dorsal scales are the longitudinal series of plates that encircle the body, but do not include the ventral scales.When counting dorsal scales, numbers are often given for three points along the body, for example 19:21:17...
.
- Vertebral
Vertebral scales, in snakes, are large scales along the top of the back of the snake, i.e., the uppermost row. They are a specialised form of dorsal scales....
.
- Ventral
In snakes, the ventral scales are the enlarged and transversely elongated scales that extend down the underside of the body from the neck to the anal scale. When counting them, the first is the anteriormost ventral scale that contacts the paraventral row of dorsal scales on either side...
, Gastrostege.
- Scales on the tail.
- Anal
In snakes, the anal scale is the scale just in front of and covering the cloacal opening. This scale can be either single or paired . When paired, the division is oblique. It is preceded by the ventral scales and followed by the subcaudal scales....
.
- Subcaudal
In snakes, the subcaudal scales are the enlarged plates on the underside of the tail. These scales may be either single or divided and are preceded by the anal scale....
, Urostege.
Other pertinent terms
- Canthus
In snakes and amphibians, the canthus, canthal ridge or canthus rostralis, is the angle between the flat crown of the head and the side of the head between the eye and the snout. More specifically, between the supraocular scale and the rostral scale. It is defined as a sharp ridge in many viperids,...
, or Canthus rostralis.
- Mental groove
Most snakes have a longitudinal groove on the underside of the head between large, paired chin shields and smaller gular scales. This is referred to as Mental groove....
.
Taxonomic importance
Scales do not play an important role in distinguishing between the
familiesIn biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
but are important at
genericIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and
specificIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
level. There is an elaborate scheme of nomenclature of scales. Scales patterns, by way of scale surface or texture, pattern and colouration and the division of the anal plate, in combination with other morphological characteristics, are the principal means of classifying snakes down to species level.
In certain areas in North America, where the diversity of snakes is not too large, easy keys based on simple identification of scales have been devised for the lay public to distinguish venomous snakes from non-venomous snakes. In other places with large biodiversity, such as Myanmar, publications caution that venomous and non-venomous snakes cannot be easily distinguished apart without careful examination.
The scales patterning may also be used for individual identification in field studies. Clipping of specific scales, such as the subcaudals, to mark individual snakes is a popular approach to population estimation by
mark and recaptureMark and recapture is a method commonly used in ecology to estimate population size. This method is most valuable when a researcher fails to detect all individuals present within a population of interest every time that researcher visits the study area...
techniques.
Distinguishing between venomous and non-venomous snakes
There is no simple way of differentiating a venomous snake from a non-venomous one merely by using a scale character. Finding out whether a snake is
venomVenom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous or not is correctly done by identification of the species of a snake with the help of experts, or in their absence, close examination of the snake and using authoritative references on the snakes of the particular geographical region to identify it. Scale patterns help to indicate the species and from the references, it can be verified if the snake species is known to be venomous or not.
Species identification using scales requires a fair degree of knowledge about snakes, their taxonomy, snake-scale nomenclature as well as familiarity with and access to scientific literature. Distinguishing by using scale diagrams whether a snake is venomous or not in the field cannot be done in the case of uncaught specimens. It is not advisable to catch a snake to check whether it is venomous or not using scale diagrams. Most books or websites provide an array of traits of the local herpetofauna, other than scale diagrams, which help to distinguish whether a snake in the field is venomous or not.
In certain regions, presence or absence of certain scales may be a quick way to distinguish non-venomous and venomous snakes, but used with care and knowledge of exceptions. For example, in
MyanmarBurma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....
, the presence or absence of loreal scales can be used to distinguish between relatively harmless Colubrids and lethally venomous Elapids. The rule of hand for this region is that the absence of a loreal scale between the nasal scale and pre-ocular scale indicates that the snake is an Elapid and hence lethal. This rule-of-thumb cannot be used without care as it cannot be applied to vipers, which have a large number of small scales on the head. A careful check would also be needed to exclude known poisonous members of the Colubrid family such as
Rhabdophis.
In South Asia, it is advisable to take the snake which has bitten a person, if it has been killed, and carry it along to the hospital for possible identification by medical staff using scale diagrams so that an informed decision can be taken them as to whether and which anti-venom is to be administered. However, attempts to catch it or kill the venomous snake are not advised as the snake may bite more people.
Cultural significance
Snakes have been a motif in human culture and religion and an object of dread and fascination all over the world. The vivid patterns of snake scales, such as the
Gaboon ViperBitis gabonica is a venomous viper species found in the rainforests and savannas of Sub-Saharan Africa. This is not only the largest member of the genus Bitis, but also the world's heaviest viperid and it has the longest fangs ,and the highest venom yield of any venomous snake...
, both repel and fascinate the human mind. Such patterns have inspired dread and awe in humans from pre-historic times and these can be seen in the art prevalent to those times. Studies of fear imagery and psychological arousal indicate that snake scales are a vital component of snake imagery. Snake scales also appear to have affected Islamic art in the form of tessallated mosaic patterns which show great similarity to snake-scale patterns.
Snakeskin, with its highly periodic cross-hatch or grid patterns, appeals to people's
aestheticsAesthetics is a branch of philosophy dealing with the nature of beauty, art, and taste, and with the creation and appreciation of beauty. It is more scientifically defined as the study of sensory or sensori-emotional values, sometimes called judgments of sentiment and taste...
and have been used to manufacture many leather articles including fashionable accessories. The use of snakeskin has however endangered snake populations and resulted in international restrictions in trade of certain snake species and populations in the form of CITES provisions. Animal lovers in many countries now propagate the use of artificial snakeskin instead, which are easily produced from embossed leather, patterned fabric, plastics and other materials.
Snake scales occur as a motif regularly in computer action games. A snake scale was portrayed as a clue in the 1982 film
Blade RunnerBlade Runner is a 1982 American science fiction film directed by Ridley Scott and starring Harrison Ford, Rutger Hauer, and Sean Young. The screenplay, written by Hampton Fancher and David Peoples, is loosely based on the novel Do Androids Dream of Electric Sheep? by Philip K...
. Snake scales also figure in popular fiction, such as the
Harry PotterHarry Potter is a series of seven fantasy novels written by the British author J. K. Rowling. The books chronicle the adventures of the adolescent wizard Harry Potter and his best friends Ron Weasley and Hermione Granger, all of whom are students at Hogwarts School of Witchcraft and Wizardry...
series (desiccated Boomslang skin is used as a raw material for concocting the Polyjuice potion), and also in teen fiction.
See also
- Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
- Canthus (snake)
In snakes and amphibians, the canthus, canthal ridge or canthus rostralis, is the angle between the flat crown of the head and the side of the head between the eye and the snout. More specifically, between the supraocular scale and the rostral scale. It is defined as a sharp ridge in many viperids,...
- Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
- Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
- Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
- Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
- Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
Further reading
, (1890),
The Fauna of British India including Ceylon and Burma, Reptilia and Batrachia. Taylor and Francis, London.
Book of Indian Reptiles and Amphibians. (2002). BNHS. Oxford University Press. Mumbai. (2004),
Snakes - The Evolution of Mystery in Nature. University of California Press, pages 22–23 (excerpted from Google Book Search beta on 7 August 2006)., , , , , (2003)
The Dangerously Venomous Snakes of Myanmar, Illustrated Checklist with Keys. Proc. Cal. Acad. Sci. 54 (24):407-462.
PDF at
Smithsonian National Museum of Natural History, Division of Amphibians and Reptiles., , (2003).
True Vipers: Natural History and Toxinology of Old World Vipers. Krieger Publishing Company, Malabar, Florida. 359 pp. ISBN 0-89464-877-2. (1943),
The Fauna of British India, Ceylon and Burma including the whole of the Indo-Chinese Sub-region, Reptilia and Amphibia. Vol I - Loricata and Testudines, Vol II-Sauria, Vol III-Serpentes. Taylor and Francis, London.
External links