Snakes are remarkable animals, successful on land, in the sea, in forests, in grasslands, in lakes, and in deserts.
Despite their sinister reputation, snakes are almost always more scared of you than you are of them. Most snakes do not act aggressive toward humans without provocation. Snakes are meat eaters and they catch prey that includes insects, birds, small
mammals, and other reptiles, sometimes including other snakes. Only about 400 of 3,000 snake species worldwide are venomous. About 25 species of venomous snakes are found in North America.
Many snakes kill their prey by constriction. In constriction, a snake suffocates its prey by tightening its hold around the chest, preventing breathing or causing direct cardiac arrest. Snakes do not kill by crushing prey. Some snakes grab prey with their teeth and then swallow it whole.
Snakes are cold-blooded. Thus, they are unable to increase their body temperature and stay active when it is cold outside. They are most active at 25-32 C (77-90 F).
Poisonous snakes inject venom using modified salivary glands. During envenomation (the bite that injects venom or poison), the venom passes from
the venom gland through a duct into the snake’s fangs, and finally into its prey.
Not all bites lead to envenomation. Snakes can regulate whether to release venom and how much to release.
“Dry Bites” (a bite where no venom is injected) occur in between 25%-50% of snake bites.
This variation is species specific with approximately 25% of pit-viper bites being “dry” and up to 50% of coral snake bites. Snake venom is a combination of numerous substances with varying effects.
In simple terms, these proteins can be divided into
1. Cytotoxins cause local tissue damage.
2. Hemotoxins cause internal bleeding .
3. Neurotoxins affect the nervous system .
4. Cardiotoxins act directly on the heart.
The number of bites and fatalities varies markedly
by geographic region. Reporting of snakebites is not
mandatory in many areas of the world, making it
difficult to determine the number of bites. Many
articles are based on population models with
multiple assumptions leading to a wide range of
Snakebites are more common in tropical regions
and in areas that are primarily agricultural. In these
areas, large numbers of people coexist with
numerous snakes. Very few deaths occur per year
from snakebites in the United States.
Venomous Snakes Most Dangerous to Humans:
Two major families of snakes account for most
venomous snakes dangerous to humans.
1. The elapid family includes:
– The cobras ( Naja and other genera) of Asia and
– The mambas ( Dendroaspis) of Africa;
– The kraits ( Bungarus) of Asia;
-The coral snakes ( Micrurus ) of the Americas; and
– The Australian elapids, which include the coastal
taipan (Oxyuranus scutellatus ), tiger snakes ( Notechis), king brown snake ( Pseudechis australis ), and death adders (Acanthophis).
Highly venomous sea snakes are closely related to
the Australian elapids.
2. The viper family includes:
– The rattlesnakes ( Crotalus) (Western diamondback rattlesnake and timber rattlesnake), moccasins ( Agkistrodon), and lance-headed vipers (Bothrops ) of the Americas;
– The saw-scaled vipers ( Echis ) of Asia and Africa;
– The Russell’s viper ( Daboia russellii) of Asia; and
– The puff adder (Bitis arietans) and Gaboon viper
( Bitis gabonica ) of Africa.
Bites by venomous snakes result in a wide range of
effects. They range from simple puncture wounds
to life-threatening illness and death. The findings
following a venomous snakebite can be misleading.
A victim can have no initial significant symptoms,
and then suddenly develop breathing difficulty and
go into shock.
NOTE: Serious venom effects can be delayed for hours. A victim who initially appears well could still become quite sick. All victims possibly bitten by a venomous snake should seek medical care without delay. The faster the patient is treated appropriately for a poisonous snakebite, the better the prognosis.
Signs and symptoms of snakebites can be broken
into a few major categories:
– Local effects: These are the effects on the local skin and tissue surrounding the bite area.
Bites by vipers and some cobras (Naja and other genera) are painful and tender. They can be severely swollen and can bleed and blister.
Some cobra venoms can also kill the tissue around the site of the bite.
– Bleeding: Bites by vipers and some Australian
elapids can cause changes in the victim’s
hematologic system causing bleeding. this bleeding
can be localized or diffuse. Internal organs can be
involved. A victim may bleed from the bite site or
bleed spontaneously from the mouth or old wounds.
Unchecked bleeding can cause shock or even
– Nervous system effects: The effect on the nervous system can be experienced locally close to the bite area or affect the nervous system directly. Venom from elapids and sea snakes can affect the nervous system directly. Cobra (Naja and other genera) and mamba (Dendroaspis ) venom can act particularly quickly by stopping the breathing muscles, resulting in death without treatment. Initially, victims may have vision problems, speaking and breathing trouble, and numbness close to or distant to the bite site.
– Muscle death: Venom from Russell’s vipers (Daboia russellii), sea snakes, and some Australian elapids can directly cause muscle death in multiple areas of the body. There can be local effect of muscle death (necrosis), or distant muscle involvement ( rhabdomyolysis). The debris from dead muscle cells can clog the kidneys, which try to filter out the proteins. This can lead to kidney failure.
– Eyes: Spitting cobras and ringhals (cobralike
snakes from Africa) can actually eject their venom
quite accurately into the eyes of their victims,
resulting in direct eye pain and damage.
Snakebite Self-Care at Home:
Common sense, hopefully, will guide a person’s
efforts if they are bitten by a snake or are witness
to someone else being bitten. Even a bite from a
nonvenomous snake requires excellent wound care.
The patient needs a tetanus booster if he or she
has not had one within 5 years. Wash the wound
with large amounts of soap and water. Inspect the
wound for broken teeth or dirt.
Take the following measures:
– Prevent a second bite or a second victim. Do
not try to catch the snake as this can lead to
additional victims or bites. Snakes can continue
to bite and inject venom with successive bites
until they run out of venom.
– Identify or be able to describe the snake, but only if
it can be done without significant risk for a second
bite or a second victim.
– Safely and rapidly transport the victim to an
emergency medical facility. Individuals should provide emergency medical care within the limits of their training.
– Remove constricting items on the victim, such as
rings or other jewelry, which could cut off blood
flow if the bite area swells.
– If a person has been bitten by a dangerous elapid
(for example, sea krait [a type of sea snake], black
and yellow sea snake) and has no major local
wound effects, a pressure immobilizer may be
A number of old first aid techniques have fallen out
of favor. Medical research supports the following
– Do NOT cut and suck. Cutting into the bite site can
damage underlying organs, increase the risk of
infection, and sucking on the bite site does not
result in venom removal. But herbalists in Nigeria often suck it and the venom is reduced.
– Do NOT use ice. Ice does not deactivate the venom and can cause frostbite .
– Do NOT use electric shocks. The shocks are not
effective and could cause burns or electrical
problems to the heart.
– Do NOT use alcohol. Alcohol may deaden the
pain, but it also makes the local blood vessels
bigger, which can increase venom absorption.
– Do NOT use tourniquets or constriction bands.
These have not been proven effective, may cause
increased tissue damage, and could cost the victim
Medical Author: Jerry R. Balentine, DO, FACEP
Medical Editor: Charles Patrick Davis, MD, PhD
Blogger: Nazeer Mukhtar RHIT, LHRO (In view)