Where snakes actually originate from still is unclear. Unquestionably, they belong to the
squamates order of scaled reptiles; their relationship to lizards is also beyond dispute. The rise
of snakes’ specific physical configuration is usually linked to hypothetical predecessors that
led a subterranean life or inhabited cracks. However, alternative hypotheses concerning the
aquatic ancestors of snakes also exist, winning increasing support from experts. Snakes are
presumed to have evolved from anguimorphous, most probably varanid-like lizards within the
process of diversification of ancestral scaled reptiles, in the Late Jurassic period about 150
million years ago. The oldest known fossil relics believed to be most likely related to snakes
are highly fragmentary and come from the Early Cretaceous, which are over 120 million
years old. The merging of the Lower and Middle Cretaceous produced Pachyrhachis
problematicus in Israel, a very intriguing marine squamate reptile. Ranked as a member of the
mosasaur family by some experts, this reptile is assumed to be an early snake with the
remnants of rear legs. Thus, Pachyrhachis may support the idea of snakes originating from
marine varanid-like lizards.
Described from the Algerian Middle Cretaceous from strata nearly 100 million years old,
Lapparentophis defrennei can be indisputably considered a snake - most probably one of
terrestrial form. In addition, other species appeared, for instance Simoliophis, supposedly a
water snake. Any exact phylogenetic ranking of these prehistoric examples referred to as
Cholophidia remains unclear for the moment. Shortly afterwards, the first family appeared:
false coral snakes, Aniliidae; this monotypic group of a single species has survived until
today. From the Upper Cretaceous, when apparently an important adaptive radiation of
primeval snakes occurred, fossil documentation shows that snakes increased in diversity,
although interpretation of their phyletic relationships greatly varies. A higher number of
lineages may have originated, from which many more recently became extinct without any
evolutionary successors. Genera that appeared at that time include Madtsoia and Gigantophis,
members of a highly successful and widespread snake group that in some places (Wonambi
genus in Australia) survived until the Pleistocene. These reptiles resemble later large boid
snakes in the size and shape of their body. Sometimes considered an important phylogenetic
node, Dinilysia, a reptile similar to a boa, is another Late Cretaceous form to emerge from
Patagonia.
It was at the beginning of the Tertiary period when monumental forms resembling
pythons or boas proliferated, while in the later Eocene the family of boas (Boidae) appeared,
including genera that were either very close to recent members or still survive today (such as
Charina). Evidence has been produced as regards members of the recent Tropidophiidae
family as well. The earliest documented blind snakes (Scolecophidi) also come from the
Eocene. In addition, the most archaic forms of so-called modern snakes Caenophidia
appeared for the first time, from an ancestral relationship of extant wart snakes
(Acrochordoidea) and ancient Colubroidea snakes, and maybe even the first colubrid snakes,
Colubridae.
However, climatic changes at the meeting of the Eocene and Oligocene periods, along
with less favorable conditions in the course of the Oligocene, brought about a vast reduction
in prehistoric Eocene snake fauna, resulting in fundamental changes in its taxonomical
structure. While some of the archaic lineages died out and Booidea and related forms shrank
to some extent, Caenophidia took the lead and later developed at an enormous rate in the
Miocene, which lasted until modern times. It is clear the evolution of snakes as such did not
proceed independently, but in accord with the general transformation of the natural world at a
time of climatic change, and in close correlation with alterations in other fauna as well,
reflecting the changing pressure of rivalry in predators and their adversaries, and responding
to diverse availability of diet. Even in the Oligocene, over 30 million years ago, colubrid
snakes (Colubridae) were expanding throughout Asia, Europe, and North America. The
oldest elapid snakes (Elapidae) in fossil records appeared in the Lower Miocene in Europe
over 20 million years ago (Palaeonaja); more recent Miocene findings also show them
inhabiting a number of places around North America, Europe, and Asia. Moreover, it is the
Miocene period when vipers (Viperidae) first appear in fossil records over 20 million years
old, these being snakes that soon proliferated as well. For instance, Vipera antiqua, a smaller
close relative of the recent V. ammodytes, ranged throughout Europe as long ago as the lower
Miocene together with V. platyspondyla, a snake closely related to the recent V. xanthina.
Throughout the Miocene adaptive radiation of modern snakes, numerous extant colubrid,
elapid and viperid genera or species evolved. In Europe, not only were there colubrid and
viperid species as more recently, but even elapids and boids could be found.
Pliocene snake fauna already featured high diversity and taxonomic similarity to that of
recent times, developments which were further affected by Pleistocene glaciations as well as
marine transgressions and shrinkage. All of the above was accompanied by changes in snake
fauna populations in different parts of the world, resulting in the map of zoogeographical
distribution of snakes and their taxonomical structure as it is known today. Currently, snakes
are present on every continent except Antarctica, including a number of islands.
Approximately 3,000 species have been described to date, mostly colubroids (Colubroidea),
in addition to the most abundant family in terms of species, Colubridae, which covers elapids
(Elapidae), viperids (Viperidae), and the less-numerous Atractaspididae family including
burrowing asps and other snakes.
The exact time when snakes became venomous is not known. However, indications of
venomousness existed as long ago as the Cretaceous Period in the Pachyrhachis genus that
can be considered a sister taxon linked to all extant snakes. This is noteworthy as it suggests
in some snake lineages venomousness could have present in their earliest evolutionary
phases. After all, laboratory experiments with saliva from recent non-venomous snakes with
archaic origins indicate a certain level of toxicity. Nevertheless, venomousness, as is
understand from a practical aspect, only exists in colubroids (Colubroidea) within the variety
of contemporary snakes. The presence of venom secretion from modified salivary glands in
the upper jaw may even have been a common trait from the very start, being apparently one
of the reasons for the extraordinary evolutionary success of these snakes. The non-existence
of venom secretion in some colubrids might obviously be only a secondary feature. In
colubroid snakes, the process of evolution was accompanied by extensive modifications to the
venomous gland, as well as the growth and development of specialized venom-delivering
apparatus. The wonderful adaptive radiation of these snakes brought about venom-specialist
families, namely in two basic parallel lineages: the solenoglyphous (viperids, Viperidae) and
proteroglyphous (elapid snakes, Elapidae). Since the Miocene period, these two families have
presented two successful alternative approaches in maximizing the potential of snake venom.
TAXONOMY OF SNAKES
Snake taxonomy is far from being completed and stable. Views of the mutual
relationships of taxonomy groups as well as particular genera are still being developed and
altered. Even today, further species are still being discovered, a number of which await
detailed scientific description, and some former species have been newly classified amongst
subspecies as a result of greater insight on their morphology. Increased knowledge and these
new findings on the classification of such snakes have also brought about changes to the
scientific names of genera and species.
Moreover, splits in high-level taxonomy groups like families and subfamilies are not
always apparent and delineating them is an unfinished chapter. For example, true sea snakes
are either placed within the elapid family (Elapidae) or under the separate Hydrophiidae
family, the sea krait subfamily (Laticaudinae) is also placed under a separate family; the
crotalids (Crotalidae) are still maintained as forming a separate group by some authors, whilst
elapid subfamilies are sometimes not listed at all due to their ambiguity. Similar problems
exist in the vast colubrid family (Colubridae), which will most probably be segregated and
rearranged at some point. Creating permanent and clear classification within such diversity as
has evolved on the Earth through the ages is definitely not an easy task, and may prove nigh
on impossible.
Furthermore, according to new findings from animal genome research, the Darwinist
understanding of a relationship based on morphology resemblance probably does not reflect
reality in terms of development and genetics. It cannot be predicted that future generations
will see an entirely altered taxonomy based on new rules respecting evolution and
relationships in a superior way.
The brief overview of venomous snake classification given below shows the recent
position of snakes in the animal system in addition to their general mutual relationships. It
should be born in mind that contemporary taxonomy knowledge indicates a monophyletic
status of many of the taxa listed, namely Colubrinae, Lamprophiinae, Natricinae, and
Elapinae. They greatly resemble polyphyletic or paraphyletic taxa instead, meaning their
nature is collective and merely temporary. Therefore, they will have to be re-classified,
although existing knowledge on the relevant phyletic relationships still does not allow for
taking such a step with the necessary responsibility.
From a practical point of view, certain problems have arisen caused by dramatic recent
development in the field of snake taxonomy. This is reflected in a large number of changes in
nomenclature published in parallel (e.g. segregating genera, shifting taxa between subspecies
and species levels, creating synonyms for previously described taxa and relocating species
under different genera), as traced by a small number of specialists. Naturally, publications in
toxicology define subjects under study following recent systematics, and on many occasions
they are err on the conservative side by employing names long established. The persistence of
the nomenclature is relatively high in relevant statistics, as well as amongst manufacturers of
antivenoms and, more generally, in the awareness of the public, including snake owners. Any
vehement acceptance of alterations in taxonomy would actually be counterproductive.
Therefore, a certain conservative approach has been maintained in the snake nomenclature
used herein; notes on the possible occurrence of older or more recent synonyms are given
where important.
Position of Snakes within the Zoological System and Overview of Families
Containing Species of Venomous Species
Class: Reptilia - Reptiles
Subclass: Lepidosauria
Order: Squamata - Scaled reptiles
Suborder: Ophidia, Serpentes - Snakes
There are 14 families under the title of non-venomous snakes, and 4 families of a
venomous type are listed below under the Colubroidea superfamily:
Superfamily: Colubroidea - Colubroid snakes
Family: Colubridae - Colubrid snakes
Venomous species are found in five colubrid subfamilies out of total of seven:
Colubrinae (about 650 species), Homalopsinae (35+ species), Lamprophiinae (205+
species), Natricinae (195+ species), and Xenodontinae (540+ species).
Family: Atractaspididae - Burrowing asps
Subfamily: Atractaspidinae - Burrowing asps (17 species)
Subfamily: Aparallactinae (40+ species)
Family: Elapidae - Elapids
Subfamily: Elapinae (130+ species)
Subfamily: Hydrophiinae (165+ species)
Family: Viperidae - Viperids
Subfamily: Azemiopinae (1 species)
Subfamily: Viperinae (65+ species)
Subfamily: Crotalinae (about 155 species)
+ stands for ‘or more’ (e.g. if any subspecies are considered species by other authors)
MORPHOLOGY OF SNAKES
Anatomically, the skeletons of snakes (Ophidia or Serpentes) lack limbs, with vestiges of
such retained in more primitive groups like boids. The kinetic and extendable skull of the
snake features a large number of articulations, the facial part joined flexibly with the lower
section of the braincase and loose ligaments on the left and right of the lower jaw. The skull
configuration allows for ingestion of large prey by dilating the jaws and pushing via alternate
movements of their right and left sides. The backbone may consist of over 300 vertebrae with
ribs that articulate with the same.
Snakes are variable in length, ranging from 15 cm up to 10 m. The largest snake ever
found was an Asian reticulated python (Python reticulatus) caught in 1912, with a length of
32 feet and 9.5 inches (999.49 cm.) Nevertheless, the South American forests are believed to
host much longer specimens of large anacondas, which are non-venomous snakes. Among
venomous examples, the king cobra (Ophiophagus hannah) reigns when it comes to length,
with a documented size of 560 cm, followed by the black mamba (Dendroaspis polylepis) at
430 cm, and the coastal taipan (Oxyuranus scutellatus) at 380 cm. The heaviest venomous
snake is the large eastern diamond-backed rattlesnake (Crotalus adamanteus) that weighs 10
kg and inhabits North America.
The western blackhead snake (Tantilla planiceps), a member of the colubrid family
(Colubridae), which has rear fangs and is found in the southwest of America, seems to be the
least venomous snake. It can grow up to 15 cm in length and feeds on worms, centipedes and
insects.
A well-muscled body, flexible skeleton and moving ribs enable snakes to move forward
using variations of motion of lateral undulation, rectilinear movement, and that resembling a
concertina, as well as side-winding on loose ground. The actual speed of movement snakes
can achieve is often overstated. The fastest snake, which is the mamba, can move at around
12 to 15 kph, i.e. equivalent to a slight jog. It is true that some places exist in the African bush
so dense with shrubs that people cannot reach such a speed. However, the notion of a mamba
chasing a man is completely absurd. The brisk attack of this snake, much like that of the
cobra, would be performed over a shorter distance, 1 to 3 m at the most, with mans’
inattention the reason for being bitten rather than impeded motion. A snake capable of such
speed is most likely to escape before being seen. Nevertheless, the motion of large vipers,
especially those with a robust body like the Bitis genus, is slow and hesitant. Therefore, a
person could stumble across one at close range, meaning a higher probability of attack due to
the snake sensing an imminent threat.
Again, the speed of a snake attacking its prey or defending itself is often exaggerated.
The measured speed of charge of the European viper after forming an ‘S-coil’ in the frontal
part of its body lasts about 0.1 s, which equals the speed of attack of 2 mps at a maximum
distance of 20 cm. However, during such a period the viper has to open its mouth, erect its
fangs, bite, and discharge its venom all at the same time. In fact, there is often a double strike.
The process described above may not be fully maintained when acting in defense, in which an
assault is only hinted at by the snake but not fully performed, including the bite and discharge
of venom; this chiefly applies to the Viperid family (Viperidae).
Snakeskin is entirely covered in scales of different shapes and is dry to the touch, with a
texture resembling slightly rough upholstery. Some snakes, saw-scaled vipers listed under the
Echis genus for example, can rub their sharp lateral scales against each other, employing such
behavior to warn a disturbing presence by creating sound. The same goes for the bony rattle
at the tips of tails of rattlesnakes belonging to the Crotalus and Sistrurus genera. The rattle
consists of free moving ossified segments, which are added to continuously each time the
snake sheds its skin. The shape, size, and number of scales are often used to identify a genus
or species. The outer horny layer of snakeskin called slough or exuvia is removed and
replaced by a new one on a periodical basis.
The eyelids of snakes are transparent and fused, hence they have a fixed stare. The pupil
is either in the shape of a ring or an upright slot, and only in extraordinary cases is it slotted
horizontally. The ring and larger pupils are usually seen in snakes with diurnal activity, while
slotted and small ring pupils tend to be features of nocturnal snakes. In some tree colubrids, a
horizontally slotted pupil serves to enhance panoramic binocular sight, essential when it
comes to properly focusing on prey. In fact, snakes perceive stationary items very badly,
which is the reason for the swinging motion that can sometimes be observed: they are
attempting to move their eyes towards their prey. This is also why an animal being hunted
stiffens instinctively.
The tongues of snakes are forked, allowing for chemosensory sensual recognition by the
creatures. The tongue can transmit chemical olfactory perceptions via a microscopic quantity
of matter, or even merely molecules, into the highly developed vomeronasal or Jacobson’s
organ, these being palate cavities equipped with sensory epithelium. Furthermore, the
olfactory organ is used to perceive smells.
The snakes of the Crotalinae subfamily possess a special auxiliary organ that cannot be
found in any other animal: thermal receptors formed by a pair of small cup-shaped cavities
placed in the upper jaw and covered with a thermo-sensitive membrane. This organ provides
exact stereotactic information for detecting a source of heat at temperatures of only 0.2 - 0.5
oC above that of the ambient atmosphere, facilitating a snake to detect prey in even complete
darkness. A blinded rattlesnake will strike its prey in 98% of cases, whilst only 27% of strikes
are successful after the thermal receptors have been covered. A similar sensory organ is found
in non-venomous boid snakes as well. In addition, it seems it is even possessed by some
venomous colubrids like Dromophis, Malpolon, Psammophis, and Rhamphiophis; however,
the pits are placed on the vertex in such snakes.
The auditory organ has changed in order to capture vibrations from the ground instead of
analyzing sound waves. These vibrations are sensed by scales on the belly, intercostal space
structures and lower jaw, the latter which vibrates the quadrate bone, with all such impulses
being transmitted to stapes and nerve endings. Consequently, snakes are deaf in the human
sense, and any attempts at driving away venomous snakes by noisy behavior while on a
family trip out is senseless but commonplace. Research made on this organ has revealed that
coughing or gunshots do not disturb snakes, although a cat walking or even a piece of paper
falling onto a writing pad is registered immediately.
One general misconception is that snakes bathe in blinding summer sunshine. Despite the
fact that sunbathing is a normal form of thermoregulatory behavior among many snakes,
namely those from colder regions, snakes are mostly unable to tolerate harsh sunlight and
high temperatures. For the majority, ideal temperatures lie between 25oC and 30oC, and they
cannot cope with anything exceeding 40oC. Any exposure to hot sun is acceptable only for a
few minutes. Indeed, if left for several dozen minutes in the sun, a snake will die even at
lower temperatures. In hot climates, in the rocks, desert, and savannah, snakes hide during the
day and come out to hunt at night. The same goes for South and Central European vipers in
extremely hot summer months, hence spending a night out under the stars and unprotected by
a tent in such a season can pose a threat in certain localities. If temperatures permanently fall
below 20oC, snakes become torpid and slow down their motions. As a result, it is common
practice to artificially cool large or dangerous snakes in order to handle them better, e.g. by
using a refrigerator.
THE VENOM APPARATUS IN SNAKES
Depending on venom production and use, venomous animals can be referred to as
cryptotoxic, i.e. not possessing any specific venom producing apparatus, and phanerotoxic,
those with the presence of a specific organ, i.e. a venomous gland.
The cryptotoxic group features beetles, such as soldier beetles termed cantharids,
molluscs, e.g. natural oysters in the summer, certain fish species in their reproductive period
or if their diet includes venomous plankton, and other creatures.
In the animals deemed phanerotoxic a venom-delivering apparatus may be absent or
present. This trait is used to classify them as passive toxic animals possessing no delivery
mechanism, or active toxic animals with a venom-delivering apparatus.
Those that are passive toxic feature an open duct of venom glands on the surface of the
skin, examples being frogs and toads, newts and salamanders.
Venomous snakes are active phanerotoxic animals. They have a specialized venomproducing
organ, a venomous gland and, with some rare exceptions, a delivery mechanism in
form of venomous fangs.
In snakes, venom is produced in a venom gland - glandula venenosa - that has developed
from the salivary gland (glandula maxillaris) in the upper jaw; it is placed behind the salivary
gland but deeper under the surface. It forms part of the digestive tract of snakes. The role of
venom is not only to kill or immobilize prey, but also to facilitate digestion. In the majority of
snakes, the size of the venomous gland largely exceeds that of the saliva gland. Indeed, it can
extend from the eye up to the end of a snake’s skull and, in some viperid snakes, it can even
stretch up to the neck. In the front section of the venomous gland, there is a slime gland
containing secretion probably designed to prevent spontaneous discharge of venom in
combination with a flap in its channel. The system opens through a duct placed in a mucous
fold near the fang channel on the base of a fang.
Fangs have developed from non-grooved teeth of the upper jaw. Snakes can be
differentiated on the basis of teeth morphology, stage of development, and location in the
upper jaw to Aglypha, which comes from the Greece glyph?, i.e. the groove, featuring nondifferentiated
teeth of the same length without longitudinal grooves or hollows, and
Glyphodonta with certain teeth furnished with grooves or hollows connected with the venom
gland. (Figure 1.)
Aglyphous snakes cover so-called non-venomous varieties like pythons, boas and many
elapid snakes.
Nevertheless, as many as two thirds of Colubridae seem to have developed the venomous
gland, referred to as Duvernoy’s gland, or a rudimentary form of it along the sides of the
upper jaw. Even though these snakes have not evolved any injection mechanism, bites from
such a ‘‘non-venomous snake’’ may very occasionally cause a limited response due to the
small amount of the gland content that is spontaneously discharged to the snake’s oral cavity.
Glyphodont snakes are venomous snakes with a venom-injecting mechanism. They can
be placed into one of three groups depending on the shape and location of their fangs.
Opistoglypha. These are snakes with rear fangs featuring a rather shallow groove in the
front of their fangs, these being larger than the rest of their teeth. They are placed at the end
of the upper jaw, mostly behind the eyes, although they can be even located closer in some
snakes, generally in the middle of the jaw. The snakes of this group are members of
venomous genera belonging to the Colubridae family. Although the venom mechanism is
rather primitive, Duvernoy’s gland opens above the venom teeth, thus ensuring the transfer of
venom to the body of prey. Their venom is quite effective. It is most necessary for tree
dwelling and bird hunting snake species to make sure they immediately kill or immobilize
their prey. Any further pursuit would be impossible in this type of habitat. Nevertheless, there
are still some opisthoglyphous colubrid genera, such as Rhabdophis, that are neither bound to
trees nor can be termed ornithophagous snakes. Biting humans is, however, rare. Penetrating
the human skin with rear fangs would require the jaws to open at a very wide angle, and the
application of any significant amount of venom via a shallow channel is improbable from
such a brief and shallow bite. From this point of view, boigas are more dangerous snakes with
their fangs placed towards to the centre of the jaw.
Proteroglypha. These snakes feature relatively small fangs placed at the front of the
upper jaw along its sides in front of other maxillary teeth. The fangs have a deep groove at the
front, which in some snake genera are encased in the form of channel. As Proteroglyphous
snakes are unable to fully control venom application using special muscles, they mostly hold
onto their prey in their jaws following a bite, injecting venom by repeatedly manipulating the
jaws. A similar situation may occur if a human is bitten due to a defensive action. There have
even been reports of snake fangs remaining in a wound after the creature itself has been
removed following an attack. The Proteroglypha group covers elapid snakes (Elapidae),
examples including cobras, mambas, kraits, taipans, sea snakes and sea kraits.
Certain cobra species can defend themselves by spraying venom, which is called spitting;
by opening its mouth, a snake reveals short fangs with openings at the front and discharges
the venom through these slots under high pressure. In fact, the droplets produced might carry
as far as a distance of several meters. Thus, the term spitting is rather inadequate to express
this kind of action. In addition, it is uncertain as to the target of the snake - the face or, more
precisely, the eyes of the individual that caused disturbance. The conical shape of the droplets
of venom might hit the eyes, just as they would any other part of the body within range.
Solenoglypha. These snakes comprise advanced groups possessing large folded fangs
along the sides of the front part of the upper jaw. The fangs include a fully closed channel
which forms a cavity. Venom is injected very promptly and in a manner well controlled by
muscles of the venomous gland. Snakes like these mostly attack by means of a rapid strike
immediately after forming an ‘S-coil’ from the front part of their bodies. Afterwards, the
mouth opens, and with fangs erect, venom is injected into the resultant wound. Then the
snake retreats swiftly, without further gripping the prey in its jaws. However, such an attack
may be repeated, and any prey that does not die on the spot or is immobilized and unmoving
is pursued. A defensive attack from these snakes may not always be complete, i.e. involving a
perfect bite and application of sufficient venom, although the manner in which it is conducted
is similar. Snakes can very probably distinguish between their hunting and defending
behavior: in over a half of bites made upon defense, either zero or a minimal quantity of
venom is discharged. The Solenoglypha include viperid snakes (Viperidae): night adders,
vipers, and rattlesnakes. (Figure 2)
Special fangs have evolved in the Atractaspididae family which are used to hunting in
narrow corridors and dens. To be able to hit their prey, they can turn and eject their front
fangs to one side and perform an attack by a swift side stab without opening their mouths. A
similar action proceeds when a snake is grasped some distance below its head and defends
itself, it can stab the hand grasping it by rapidly shaking its head to either side.
The fangs are covered by a mucous fold pulled over them. In the course of time, fangs are
renewed in most snakes, with new pairs growing behind the older and larger ones. Indeed, it
is no exception to find several fangs in a row, for instance in the Bitis genus of vipers, where
up to six successive fangs can be found in Bitis gabonica, also visible in bite marks on
humans.
Fang size may greatly vary; in smaller proteroglyphous snakes, they can grow to a mere 2
or 3 mm. In sea snakes and sea kraits, fangs are usually unable to penetrate neoprene diving
suits. However, the erectile fangs of larger vipers and rattlesnakes can reach several
centimeters in length, the record holder being the Gabon viper (Bitis gabonica) which boasts
fangs 4-5 cm long.
DISTRIBUTION OF VENOMOUS SNAKES
Venomous snakes inhabit a major part of the Earth’s surface, be it dry land or sea.
Nevertheless, places without snakes do actually exist as well. In general, they involve cold
regions with an adverse climate, or islands that snakes could not reach by migrating through
evolution or via the intervention of humans.
In the southern hemisphere, snakes do not inhabit Antarctica, the entire territory of Chile,
which was blocked to them from the east due to the Andes Mountains causing a barrier; then
there are the Gal?pagos Islands, New Zealand and Madagascar. As regards Oceania, they live
in Polynesia, Micronesia, the New Hebrides, the Loyalty Islands and the Hawaiian Islands.
Nonetheless, sea snakes are found in the territory of the Pacific Ocean, but they do not extend
to the Atlantic Ocean. The most southerly venomous snake is one of the lanceheads
(Bothrops), with its territory extending as far as Tierra del Fuego.
In the northern hemisphere, the situation is more complicated from a geographical point
of view. The northerly limitation on territory in Europe and Asia, which affects the common
viper (Vipera berus), is defined by the Arctic Circle. The creature also does not live in the far
northern regions of Norway, Sweden, Finland and Russia, but can occasionally appear in the
polar circle. Its home range continues throughout Asia, and ends below the 60th parallel north
of Sakhalin Island. To the west, this species does not inhabit Ireland, Iceland and Greenland.
In North America, the territory of venomous snakes approximately follows the 50th parallel,
which is the US and Canadian border, where they can be found practically only in the vicinity
of the Great Lakes and on certain islands around eastern Canada.
Within the colder parts of the territory, venomous snakes cannot be found on the Cape
Verde Islands, the Canary Islands, the Balearic Islands, or in Corsica, Sardinia, Malta, Crete
and on other Greek islands. In terms of Central America, they do not occur on any Caribbean
island except Tobago, Trinidad, Saint Lucia and Martinique, where venomous snakes do
reside; see Figure 3.
As already mentioned, sea snakes inhabit neither the Atlantic Ocean nor the
Mediterranean Sea, but occur in the Indian and Pacific Ocean. Most of them dwell in the
waters that stretch between the Gulf of Persia and Indo-Chinese and Australian regions. Some
extend over the Pacific Ocean as far as the US coast.
Regarding elevation, most snakes inhabit localities below 2,000-2,500 meters above sea
level; but even here there are some exceptions. For example, the common viper (Vipera
berus) may ascend to 3,000 meters above sea level in the Alps and Scandinavian mountains,
and the central plateau dusky rattlesnake (Crotalus triseriatus) of Central America is able to
live as high up as 4,400 meters above sea level. The Himalayan pit viper (Gloydius
himalayanus), a dweller of forests, holds the record for altitude, as 3,000 - 4,000 meters is
usual for it, but this snake has even been discovered at a height of 5,300 meters, at the very
edge of a glacial zone.
Although venomous snakes have adapted to living in nearly any habitat globally,
particular groups of these snakes prefer specific types of landscapes. For example, Viperinae
snakes favor quite dry and open ground, often wooded areas in sub-mountainous and
mountainous ranges with sand or stony substrates. With some exceptions, the Gabon and
rhinoceros vipers avoid dense forested enclaves with restricted sunlight. However, Atheris,
one of the Viperinae genera, has specialized in hunting and dwelling in trees and bushes.
Crotalinae snakes have similar requirements concerning landscape: they reside in
savannahs, sparse woodland and thickets in the sub-mountains and mountains of America and
Asia. However, there are exceptions to the rule in this group as well. Several lancehead
(Bothrops) and Asian pit viper (Trimeresurus) species are frequent inhabitants of forests and
their surroundings, while some species of the Agkistrodon genus prefer proximity to water.
Unlike the viperids (Viperidae), most elapid (Elapidae) species seem to consider ideal
habitats to be damp or dense tropical forests, or at the very least the environs of such, as do a
number of Asian cobra species of Naja and Ophiophagus genera, as well as coral snakes of
the Micrurus genus.
However, African cobras and mambas largely inhabit localities of grass savannahs in
addition to shrubby and sparse bush environments, with cobras living a terrestrial life and
mambas as tree dwellers. Similar dry or even partial desert locations are resided in by some
Australian coral snakes, too.
Sea snakes that once again belong to the group of elapid snakes (Elapidae) largely prefer
salt water; they are less common in brackish waters and rare in fresh waters.
The Atractaspididae snakes family members lead an intriguing way of life - they inhabit
tunnels and dens underground, where they also hunt.
Boigas, venomous colubrids, are chiefly tree or shrub dwellers, while damp and forested
enclaves prevail as far as Natricinae snakes are concerned.
ETHOLOGY BASIS,HUNTING, ATTACKS AND DEFENSE
When hunting, venomous snakes use solely their venom apparatus. A snakebite thereby
means immediate or delayed paralysis, immobilization and eventual death to prey. Therefore,
the venom mechanism and toxins are tailored to the type of hunting and intended prey.
Some of the Atractaspididae snakes, more specifically, burrowing asps (Atractaspis),
which hunt for rodents in narrow tunnels underground, can slightly open their mouths by
releasing the lower jaw and lash out with their long fangs by shifting the head aside and
moving backward. A similar method is also used in defense; when gripped behind its head,
the snake can stab with its fangs, employing side movements of its head and jaws.
The venomous arboreal colubrids Thelotornis and Dispholidus, which principally hunt
birds and chameleons, possess rear fangs and toxins effective enough for birds. The rear
position of their fangs poses some limitation for these snakes in that their prey has to be rather
small, as the angle of the open mouth does not always allow for larger animals to be bitten
successfully. Nonetheless, they are efficient predators with good motional skills and eyesight,
essential qualities for this style of hunting. The effective toxins kill prey in a very short time
due to hunted animals being held in the snake’s mouth, this is in addition to frequently being
grasped by the creature’s coiled body. If prey is let go of too soon, it could escape to beyond
the snake’s reach. Considering the position of the fangs in the rear part of the upper jaw,
envenoming a human via a defensive bite would be technically too complicated for most
representatives of the Colubridae family. With this in mind, boigas are the most dangerous
snakes, with their fangs placed in the middle of their upper jaw.
Elapid snakes (Elapidae) are mostly terrestrial animals that hunt small mammals, frogs,
lizards and other reptiles, although this family does includes marine piscivorous snakes.
These representatives excel in terms of motional skills and are able to paralyze prey very
swiftly owing to their venom, which contains effective neurotoxins. Most of them hold their
prey in their mouths, pumping venom into the animal by repeatedly clasping their jaws -
much like chewing - as venom discharge is not controlled by the muscles of the venomous
gland. In coral snakes, cobras for instance, the speed of movement over solid surfaces and
that of potential attack should be paid heed to by snake keepers and hunters. When in danger,
a large cobra is capable of performing an assault over a distance of several meters in just
fractions of a second. However, the speed and aggressiveness of the mamba (Dendroaspis) is
often overstated. Even though mambas are probably the quickest snakes - the velocity and
level of threat involved is described in the snake morphology chapter - popular belief of their
pace is based on myth. While it is true that a bite from a mamba proves mortal without
treatment due to the content of neurotoxins, it is still not ranked highly in snake envenoming
epidemiology in its home territories. When snake collecting in south-east Senegal, only four
black mamba (Dendroaspis polylepis) individuals were captured out of total 1,280 snakes.
Considering the fact this snake is not very rare, a possible explanation may be timely escape
from the area under survey. Much like other snakes, mambas are not keen on making contact
with humans, and intentional attacks on people are not listed amongst their behavioral traits.
Any possible case of a mamba approaching a man might be explained as inquisitive behavior.
They will attack only if sensing a threat, just like any other snake, although the swiftness of
this action can exceed the response of humans.
Marine coral snakes - sea snakes and sea kraits - are hunters of small fish largely in the
vicinity of coral reefs. They may often follow or pursue divers, occasionally with even close
physical contact taking place in form of twining around legs. Nonetheless, occurrences of
snakebite are rare, in fact, their fangs are so small they are incapable of penetrating a
neoprene diving suit, and defensive biting is not typical of these snakes. Moreover, there are
instances on record of children playing with sea snakes washed up on beaches, but no child
has been bitten. It is more usual for fishermen to come into contact with sea snakes, although
such individuals are at risk of snakebite to some extent anyway.
The viperid family (Viperidae), an advanced snake taxon in terms of evolution, can hunt
prey by swift and sometimes repeated bites using erected fangs. They do not hold prey in
their mouths as the bitten animal is subsequently pursued. Viperids’ venom is a complex of
toxins and enzymes affecting a number of vital systems, meaning death to their prey even if
the attack is rather unsuccessful. The biting of humans by viperids, namely vipers (Viperinae)
is nothing rare in the wild. The higher rate of incidence is caused by the lesser speed of the
viper. While elapid snakes (Elapidae) can mostly escape from humans very quickly, vipers do
so much slower, whilst some species, like the Bitis genus, show little enthusiasm to get away.
This can expose such snakes to direct contact with humans much more often. Attacking prey
and defensive attacks in viperids follow certain rules and procedures, see chapter 1.3
Morphology of snakes. The anatomical configuration of the venom mechanism, as well as the
ability to differentiate between predation and defense is discernable in viperids by a high rate
of so-called dry bites - those where venom is not released - and mere warnings of a strike as a
deterrent.
To put off an enemy, snakes employ the most basic sound they can emit - a hiss - despite
not being able to hear. In addition, saw-scaled vipers (Echis) and rattlesnakes (Crotalus) have
another method of warning by sound. When threatened, the Echis viper emits a crisp or
strident (sharp) sound by rubbing together coils of its body, which is covered in thick ridged
scales. The use of the rattle on the tail of rattlesnakes (Crotalus) serves the same purpose. The
speculation that this is a passive form of audible defense to deter herds of running animals in
an open plain should not be ruled out. Other forms of deterrence include visibly enlarging the
body. This is performed by cobras by erecting and typically extending the ribs in the front
part of the body to form a hood, whereas the Gabon viper (Bitis gabonica) inflates its neck.
Another example is the opening of the mouth to display the different color inside, which
could function so as to make the creature more visible and simulate an attack. For instance, as
the names suggest, the inner part of mouth of the western cottonmouth (Agkistrodon
piscivorus leucostoma) is white, and in the black mamba (Dendroaspis polylepis) it is black.
The speed and behavior of venomous snakes relates to the safe distance one can stand
from them as well as estimating the potential of attack. The swifter the snake is when moving
and performing an attack, added to which the physically larger the creature, the greater the
distance that must be kept for safety’s sake. In cobras and mambas, this can be up to several
meters depending on the size of the snake. Considering the 4-meter black mamba
(Dendroaspis polylepis) or the king cobra (Ophiophagus hannah) of 5 meters, these snakes, if
ideally positioned, are able to carry out a surprise attack over a distance of nearly two meters
without any prior movement. Compared to the species above, the lesser Vipera and Cerastes
genera, or even the rapid saw-scaled vipers (Echis), prove incapable of placing a bite at a
distance of over 50 cm. Such a short distance can be considered safe with the ‘lazy’ Gabon
viper as well, in spite of its size, unless it is poised in a threatening position. However, the
information above definitely cannot not be applied to the large and short-tempered Crotalus
and Bothrops genera, which are capable of a flying attack of over 1 meter from a point of
attack, despite their mighty bodies.
When determining a distance to be kept from a snake, the poise of the creature is crucial.
A safe distance from a snake that is lying outstretched, escaping or quietly resting is sure to
be reduced and any attack is less probable, unlike in the case of a viper coiled up with its head
elevated and ready to strike, a rattlesnake that has formed the typical coil at the front part of
its body or an erect cobra threatening to attack.
When kept in a terrarium, an attacking snake protects itself and its limited territory. In
fact, keeping any form of safe distance is practically impossible. The apparent calm of the
hidden snake should not be mistakenly relied upon, and placing one’s hands inside the
terrarium in the presence of the snake is likely to wind up in a bite.
Another form of defense employed by snakes and animals alike is that of protective
coloring. Spotting the black mamba or a Trimeresurus snake in tree branches, the Gabon
viper in fallen leaves or the Levantine viper (Vipera lebetina) in stony and sandy
environments is sure to require a lot of attention.
In addition, certain snakes, the ringhals (Hemachatus hemachatus) for instance, feature
an ability to play dead, known as thanatosis, when the snake lies on its back, exposing its
lighter underside, coiling up and opening its mouth. The snake’s mouth hangs free in order to
resemble bleeding. This puts potential aggressors off due to gathering carrion, although even
snakes in this position can prove dangerous to hunters or curious individuals, as they can,
nevertheless, bite.
Naturally, escape is the snake’s principal and initial form of defense and, as mentioned
earlier, when walking around normally, one would hard pushed to actually see a snake even if
the area is rife with them. After all, snakes do not crave attention.
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