Snakes are scaly, legless reptiles without any external ear and movable eyelids. The entire length of the body is flexible.

Snakes are among the most dangerous venom possessing animals. However, all types are not poisonous. Out of the more than 2,500 species of snakes, something more than 300 species are only poisonous. Again not all of them, are dangerous to human beings.

Zoologically, snakes belong to the class Reptilia, order squamata and sub-order serpentes (snakes). They have several superfamilies, families, subfamilies and tribes.

Snakes are of various sizes, morphology, colours and habits. They have some peculiarities in their sense organs, food habit, activities, body temperature, reproduction and behaviour.

Sense organs of snakes –

1. Vision – Snakes have eyes without eyelids. Elapidae family has circular pupils and viperidae, mostly vertically elongated pupils. Vision is most effective for moving’objects and a static object may not stimulate the visual capacity of a snake.

Touch sensation is quite effective in snakes except in some rough thick-scaled snakes which may not feel light touch.

Hearing capacity of snakes is doubtful. They have no external ear. Though they have middle ear, there is no definite proof that snakes can hear.

Smell – The two small nostrils function well and snakes have a strong smell sensation.

Vibration – Though snakes may not hear sounds, they can recognise moving objects from the vibration of the ground.

Jacobson’s sense organ – Snakes have some special sensitive cells in the palate called Jacobson’s organ. The flicking forked tongue of the snake carry stimuli from the air which when touches the palate, helps the snake to know the presence of a thing in the area.

Sense related to temperature variation – In pit vipers there is a pit or depression on each side of the head in between the eye and the nostril. These are sensitive to any temperature variation in the area in contrast with the environmental temperature. Thus, pit vipers can recognise and locate any animal or anything having a temperature different than the environment. Pythons also have pits with similar function at the ends of the lips, though less sensitive than pits of the vipers.

Jacobson’s organ, pits and vibration of the ground help the snakes to move freely and safely during the night hours.

Food habit – Most of the snakes are carnivorous. They eat insects, toads, lizards, rodents, chicks and even other snakes. Pythons eat even larger animals like small goats or lambs. They swallow the whole animal without chewing. The shape of their jaws allow swallowing of comparatively bigger preys. Depending on the type of the snake and the size of the meal, a snake may take food even once in a week or a month only. During hibernation period, snakes refrain from taking any food as they refrain from doing any other exercise.

Activities – Snakes cease to be active for some time during the winter when they go in hibernation. During this period their metabolic activities are extremely low and they remain dormant in all senses. Their body temperature also falls.

Body temperature – Snakes cannot generate heat and their body temperature varies with the environmental temperature. During hibernation in winter, in cold zones their body temperature falls markedly and they survive a body temperature as low as 4°C. They die if the body temperature comes down to 0°C. Between this range some of them survive, some die. On the other hand, if during hibernation environmental temperature goes up, then the snake may die due to starvation, after the stored food of the body is exhausted due to increased metabolism.

Reproduction – Most of the elapidae lay eggs and most of the viperidae give birth to new ones. Eggs are layed in protected places. But, except king cobra and a few others, snakes do not take any care of the eggs. Eggs are hatched with the help of natural atmospheric temperature. King cobra builds nest to lay eggs and sits on the eggs protecting them and also helping them to hatch out by generating some heat by shivering its body. The vipers keep their eggs in the oviducts till they are hatched. There is exchange of respiratory gases (oxygen and carbon di-oxide) between the snakes body fluid and eggs through the thin layer covering the eggs. The young ones, after hatching out of the eggs or birth from the mother’ body, are ready to fight, bite (venomous) and search out their food with equal efficiency like adults. They reach the age of reproduction by 3 – 5 years.

Difference between Cobra and Viper
Features Cobra Viper
Head Smaller and slender, covered with large scale Larger, triangular and covered mostly with smaller scales.
Pupils Circular Vertical, slit-like
Neck  Not prominent Narrow prominent neck
Tail Less tapering More tapering
Fangs Shorter and grooved Longer and channelled
Other teeth Present in the upper jaw Absent
Reproduction Oviparous, by laying eggs which hatch externally Viviparous, gives birth to young ones. Eggs are hatched inside the body of the mother
Venom Mostly neurotoxic  Mostly haemotoxic.

Behaviour – Most snakes are docile in nature. When annoyed or disturbed, they make a hissing sound as a threat. When attacked or cornered or angry, they bite. King cobra is by nature to an extent aggressive and pursue its enemy.

Snakes are found all over the world except in Greenland, Ireland and Newzealand.

Features of poisonous snakes – Poisonous snakes are of various sizes and colours. The most important feature is that, they have fangs, one each on either side of the upper gum, which are either hollow or grooved. These are actually the biting teeth of the snakes, and are connected with salivary glands possessing venom. Ordinarily, they remain folded but during biting they become vertical. Tail of poisonous snakes are usually compressed and stouter. Their ventral scales are larger, each pass across the whole of the breadth of the ventral surface. Head scales are usually small or large as in pit vipers with pits in between eye and nose on each side. The scales may be large with the third labial scale touching the eye and nose margins or with 4 infra-labial scales, the fourth being the largest. Most of them are usually nocturnal in habit.

Snake venom:

The bite of a poisonous snake inject venom or toxic substances in the tissue, at the site of bite. Venom is secreted by special glands near the upper jaw of the snakes which are akin to human parotid glands. During the process of bite, the glands are pressed and the venom is squeezed and channelled through the grooves or channels of the fangs.

Banded KraitFreshly secreted venom is transparent and pale. On storing and exposure to light, it becomes yellowish and opaque. Venom in winter is thicker than venom secreted in summer. But venom is more toxic during summer than during winter (Deoras, P. J. of Haffkine Institute, Bombay).

Venoms are proteinous in nature most of which are glycopolypeptides and are enzymatic in their actions. A good number of these have been chemically identified from various snakes and each variety of snake contains some of them. Some of these toxic substances are neurotoxic, some haemotoxic and some act on some other tissues. The constituents of different snake venoms are – Neurotoxin, haemolysin, proteolysin, fibrino lysin, cholinesterase, coagulase, cardiotoxin, nucleotidase, hyaluronidase, phospholipase-A etc. The Cobra varieties primarily possess neurotoxic agents and viper varieties primarily possess haemotoxic agents.

ActioCommon Kraitn of venoms

Locally, there is irritation and ecchymosis at the site of the bite. Systemic action may start as early as within 10 minutes. There is increased catecholamines in the circulation. There is depression of spinal cord and medulla. Some of the venoms inhibit blood coagulability, others cause intravascular clotting of blood by thrombokinase and calcium-like action or directly changing fibrinogen to fibrin. In some venom, there is heparinase which causes clotting by destroying heparin. However, fibrinolysin present in the venom, breaks down fibrin and causes lysis of the clot. Blood fibrinogen is grossly reduced. Haemolysin and phospholipase-A cause haemolysis. Human and dog red cells are more susceptible than cow or goat red cells.

Bradykinin like action and loss of fluid through the damaged endothelium result in the fall of blood pressure. Cobra venom however causes rise of blood pressure by vaso-constriction.

Respiratory paralysis is due to curare-like action and also due to action on the central nervous system. 3rd, 4th and 6th cranial nerves are affected serially, 9th and 10th nerves are affected later.

Absorption – Absorption cannot occur through unbroken skin or mucus membrane. Absorption from subcutaneous injection is quite rapid.

Fatal dose and amount injected in one bite –
Snakes Fatal dose Quantity injected in one bite
Cobra 15 mg More than 200 mg
King Cobra 12 mg About 100 mg
Common Krait 1mg More than 5 mg
Banded Krait 10 mg More than 40 mg
Russell Viper 40 mg About 70 mg
Green pit Viper 100 mg About 15 mg

Fatal period –

For cobra varieties -1/2 hr. to 24 hrs.

For viper varieties -1 to 3,4 days.

Signs and symptoms – With cobra bite local pain is less, with less local reaction and swelling. Two fang marks are present which ooze less. The area gradually becomes bluish. There are malaise, drowsiness, nausea, vomiting, flushing of face. Pulse is initially normal which is later depressed and irregular. Blood pressure may remain unaffected. Muscles of the extremities become weak. Paralysis ensues in the lower limbs first, which ascends gradually affecting the respiratory muscles including the diaphragm. Respiration becomes difficult. With paralysis of muscles of neck there is drooping of head. There is difficulty in swallowing and articulation of speech. There are frothing from the mouth, drooping of lower lip and eye lids. The vision becomes blurred with loss of accommodation reflex. Death is due to respiratory failure.

With krait bite, the signs symptoms are less rapid. There is no nausea and frothing but drowsiness is more.

With viper bite there is more local reaction with more local pain and oozing. Local necrosis is extensive, which may lead to gangrene. The pulse is weak and irregular. Blood pressure falls with signs of collapse. There is bleeding from nose and in urine. Death occurs due to circulatory failure in the early phase and due to haemorrhagic and haemolytic complications at the later phase.

Treatment – 1. Two tourniquets are to be applied on the limb, proximal to the site of bite. 2. Multiple incisions are given over the bite marks, depth of the incisions being not less than 2/3rd of the measurement between the two fangmarks (bite marks). After the incisions are given, as much venom (with local tissue fluid) as possible is squeezed out or sucked out by a sucker or by mouth. 3. If suction is of not much help then the local tissue around the site of bite may be infiltrated with injection of 2 ml. of weak potassium permanganate solution or 2.5% solution of hypochlorite of lime or 3 ml. of polyvalent antivenene or antivenom serum. 4. After the first hour, each of the tourniquets used should be released alternately for 10 – 15 seconds at an interval of 10 – 15 minutes. 5. Polyvalent anti-snake-venom serum (prepared in Haffkine’s Institute, Bombay, by injecting horses with snake venom of both cobra and viper variety) is given intravenously in the dose of 20 ml. prepared freshly by dissolving the powdered serum in distilled water. Half of the initial dose is repeated at every 2 hours interval, if necessary. Before injecting the dose of the serum, it should be tested for sensitivity of the patient. 6. If antisnake venom serum is not available or if the patient is very sensitive to it then, polyvalent antivenene (a drug prepared at Kasauli) may be used as a substitute. Cortisone, adrenaline, anti-histamine and nikethamide may be used as supportive treatment. 8. If antivenom serum or antivenene is not readily available then, the limb may be kept dipped in water at 10 – 15°C. 9. Complications should be treated accordingly.

Postmortem findings – The site of bite is swollen and bluish with oozing of reddish fluid from the bite-punctures, which are usually two in number. When death occurs after a day or two, effects of necrosis may predominate with gangrenous change in some. The non-gangrenous lesions on dissection show tissue oedema with ecchymosis. These local findings are more common in viper bite cases. In cobra bite, there are some oedema and ecchymosis but necrosis and gangrenous change is uncommon. In cobra bite, there may be evidence of frothy discharge from the mouth. Internally, in case of cobra bite, pulmonary oedema is a comparatively common finding. In case of viper bite, haemorrhage in the organs and in the undersurface of serous or mucus coverings are common. Intra-vascular clotting with microscopic damage of the endothelium is also common in viper bite. Urine in urinary bladder shows presence of haemo¬globin and albumin in these cases. Micros-copically, the lymph node sacs show presence of R.B.C. and phagocytes.

Medicolegal aspects – Snake bite deaths are almost exclusively accidental, occurring mostly in agricultural fields, gardens and in village roads and fields. Snake charmers occasionally are the victims of accidental snake bite. Occasionally suicidal cases are recorded in snake charmers. Death may occur due to circulatory collapse, out of fear even in non-venomous snake bite. Snakes cannot bite outside the radius of the length of its erected body part. A snake does not bite if a person does not move his body parts, and stands still. Shoes protect feet successfully from snake bites.


Cantheride is locally irritant and also a nephrotoxic agent. It is an insect, also known as spanish fly. It is about 1.5 cm long, shining greenish in appearance.

Active Principle – Cantheridin.

Both crushed cantheride and cantheridin are toxic.

Uses – As counter irritant and in other medicinal preparations.

Fatal dose – Crushed cantheride – 1.5 gm., Cantheridin – 30 mgm.

Fatal period – 12 – 24 hrs.

Action – Locally irritant, Remotely – nephro¬toxic.

Signs and symptoms – External application causes burning pain, redness and vesiculation. When ingested – Burning pain in throat and abdomen, vomiting, scanty urination, haematuria, albuminuria, painful swelling of penis, blood tinged mucus stool, straining during motion, C.V.S. collapse, renal failure, convulsion, coma, death.

Treatment – Restriction of fat by mouth as fat dissolves cantheridin and helps absorption, Demulcent drink, stomach wash, plenty water, and symptomatic treatment.

Postmortem findings – Signs of irritation in mouth oesophagus, stomach. StomachE swollen, soft haemorrhagic, contains shining greenish particles of exoskeleton of the insect. Kidneys congested swollen with haemorrhage in pelvis and calices. Urinary bladder contains reddish (for blood) urine with haemorrhagic areas on mucous membranes. Haemorrhage under epicardium and endocardium. Lungs – congested, subplueral haemorrhagic spots.

Circumstances of poisoning – 1. Counter irritant preparation in home may be taken accidentally. Suicide is rare. Homicidal use is far more rare. Used as an abortifacient agent. Used to increase libido in males.


SCORPION VENOMThe end part of the tail of a scorpion has two poison glands and a sting. An agitated scorpion presses its sting onto the body of the victim injecting the venom and sometime leaves the broken tip of the sting in the tissue.

The venom is proteinous substance and is haemotoxic and neurotoxic in action.

Signs and symptoms – Locally, there is pain and oedema. Systemic effects appear within 15 g 30 minutes. There are anxiety, sweating, salivation and nasal secretion. Pulse is slow and B. P. is raised. Muscular fasciculation and convulsion may occur. Also, there may be pulmonary oedema, cardiac arrhythmia and myocardial infarction, particularly of the papillary muscles.

Treatment – A tourniquet is applied proximal to the site of sting. Multiple punctures or incisions to squeeze out or suck out the venom is useful. The broken sting is taken out if left at the site. Specific antivenin, if available, should be injected, both for systemic action and local infiltration. Calcium gluconate is given I. V. for reducing local pain and oedema. Barbiturate or chlorpromazine is help-ful to counter convulsion and sedate the patient. Atropine sulphate prevents pulmonary oedema.

Postmortem findings – Fatality is common in children. The affected site is swollen. The sting may be present at the site. On dissection the surrounding tissue, may show some degree of ecchymosis. Infarction of myocardium and pulmonary oedema may be noticed in some cases.


The sting of bees injects histamine, cardiotoxin and phospholipase-A. Venoms of wasps and hornets contain histamine, serotonin, curare-like substance and kinin.

Stinging by these insects causes local pain and oedema. Systemic effects of the venoms are seen in multiple stingings when death also may occur with signs of collapse with sweating, fall of blood pressure. There may be nausea and bronchospasm.

Treatment – Epinephrin HCL – 0.3 mg S.C., Ca-gluconate 1-2 gm IV, Glycocorticoids I.M., Artificial respiration, O2 inhalation, and Antihistaminic cream locally.


RED ANTSBite by red (fire) ants causes injection of an alkaloid, solenopsin-A. It has haemolytic and phytotoxic actions. At the site of bite there is urticarial lesion followed by pustulation. There may be raised blood pressure, retrosternal pain and respiratory difficulty.

Treatment – Adrenaline & antihistaminic drugs.


They secrete phenol, quinone and cyanogen from the base of their feet which may produce ulcer.


Black spider (Black widow spider) bite is toxic. There is pain at the site of bite. After half an hour or more there are cramps at the site of bite which extend upwards. There may be nausea and vomiting and the B.P. may be raised. Action on the C. N.S. and at the nerve endings of the diaphragm, may cause respiratory problem.

Treatment – Sedatives, Ca-gluconate, combination of Neostigmine and Atropine (0.5 mg each) and Curariform drug.


Bite causes injection of haemolysin and norepinephrine.

There is painful ulceration at the site of bite. Some may develop nausea, vomiting, fever, haematuria, albuminuria and arthralgia.

Treatment – Symptomatic.


These are big land lizards. Two varieties, e.g. Arizona and Mexican gila monsters have been studied in some length. They are known to carry poison and inject the same in bites. Both upper jaw and lower jaw teeth possess grooves to channel the poison. Their average sizes vary around 15″ – 20″. Gila monsters are also available in Bangladesh and northern part of West Bengal where they are commonly termed a ‘Gui-saap’. They are larger than the American variety, and are believed to possess venom in their saliva. There has been no authentic study in details.


Salamanders have deadly poisonous glands on different parts of the body. They may be on the dorsal aspect along the midline or may be in rows in that area. ‘Parotid’ poisonous glands are situated in clusters in both sides of head in European earth salamanders. In some, the poisonous glands are distributed all around the body surface. The poison can be spilled out of the glands up to a few inches. The active principles in the venom are alkaloidal in nature. The different alkaloids are samandarone, samandarine, O-acetyl-samandarine, samandari- dine, samandanine, samandenone, samanine, cycloneosamandione, cycloneosamandaridine.

The alkaloids are poisonous to all vertebrates. Externally, contact with the venom causes burning sensation of eyes and mouth. When in circulation, there are restlessness, weak respiration, irregular pulse, convulsion which continues for a few minutes followed by relaxation and stronger convulsion. The B.P. is raised, pupils are dilated. There are loss of reflexes and paralysis of limbs. Action is on the C.N.S., particularly the spinal cord. Death occurs due to respiratory failure.

On postmortem examination, the organs are congested. There is haemorrhage in organs, particularly lungs and spinal cord.


Toads and frogs have two types of glands on their body surface. The mucus glands are smaller and shallower, distributed all around and their secretion is thin which lubricates the surface to make it easy to slip out when caught. The granular glands are larger in size and their secretion is thick and creamy. These glands are more defined in their locations. The two parotid glands situated behind the orbital crests or over the shoulders are the largest of the granular variety. Smaller granular glands may be present at other sites, like, near the fingers or toes.

Secretion of these glands are poisonous. But a toad or a frog does not liberate venom by itself. This is liberated due to wrong handling or manouvering of the animal. The active principles available in toads and frogs are many, e.g. serotonin, N-methyl-serotonin, butenine, dehydro-bufotenine, bufotenidine, bufothionine, bufo-viridine, leptodactyline, peptides like bradykinin, histamine, steroidal alkaloids, bufogenins, bufotoxins etc.

Tick Paralysis – Occurs due to bite by the tick Rhipicephalus Sanguineus.


Among the venomous aquatic animals, some are vertebrates and some are invertebrates. Among the vertebrates, sea snakes and venomous fishes (icthioacanthotoxic fishes) are mentionable. Poisonous fishes are described in this chapter in short. Among the invertebrates, there are, shells, mussels, squids, crustaceans, jelly fish. Poisoning due to aquatic animals may occur by way of biting (sea snakes) stinging (spines of various venomous fishes), surface contact (jelly fish) and consumption as food (shells, mussels, squids and crustacians).


Stingray – The sting is located in the dorsal aspect of the tail either near the base of the tail or at some place in its length. The venom is originated in the ventrolateral glandular tissue and the adjacent cuneiform area. The sting or the spine has furrows.

The venom of the stingray fish causes vasoconstriction in large dose and vasodilatation followed by vasoconstriction in small doSe. It also inhibits auricular and ventricular contractions and dilatation.

Signs and symptoms – There is intense, sharp, shooting, spasmodic or throbbing pair; at the site. The area is swollen and there may be some degree necrosis of the marginal tissue. There may be nausea, vomiting, faintness, vertigo, diarrhoea, sweating, fall of blood pressure (due to ordinary mild dose injection), arrhythmia and muscular paralysis (spastic or flaccid).

Poisoning occurs usually in divers.

Horn Sharks – There are two dorsal spines at the anterior margins of the two dorsal fins. The spines are grooved anteriorly. Near the base of the spines, there are glandular cells. Venom production is of holocrine type.

Signs and symptoms – There is immediate intense stabbing pain after stinging with swelling and redness of the affected part. Death may occur due to shock.

Catfish – A catfish has three stings, one dorsal in front of the anterior dorsal fin and two pectoral stings one in each side in front of pectoral fins. The venomous glands are axillary glands for the pectoral sting and glandular structures situated at the anterolateral and posterolateral margins at the base of the dorsal sting.

The venom of the catfish consists both neurotoxic and haemotoxic agents.

Signs and symptoms – Catfish stinging causes intense pain which may lead to primary shock resulting in death in a few cases. Respiratory distress is a common feature. The wound may get secondary infection and may take long time to heal.


Zebra-fish and stone-fish have 13 dorsal spines, 3 anal spines and 2 pelvic spines, with associated venom glands.

Scorpion-fish proper has 12 dorsal spines, 3 anal spines and 2 pelvic spines with associated venom glands.

Venoms of scorpion-fishes consist of neurotoxic, haemotoxic and cardiotoxic agents.

Signs and symptoms – There is pain at the injured site which is most intense with stone-fish stinging. The area becomes bluish with a surrounding red zone and is swollen and warm. There may be nausea, vomiting, nervous disturbances, convulsion, delirium, fever, pain in the joints, respiratory distress and cardiac failure. There may be lymphadenitis and lymphangitis. Death may occur.


In toad-fish there are 2 dorsal spines and 2 opercular spines with associated venom glands.

Signs and symptoms – Local pain with swelling, redness and warming of the affected area.


They have 5-7 dorsal {spines and 2 opercular spines with associated venom glands. The venom stimulates sensory motor cortex and ‘ is also cardiotoxic. There is also paralytic effect on respiratory muscles.

There is extreme pain at the site of stinging where gradually tingling and numbness develop. The area is first ischemic which gradually becomes red and swollen, which may persist for over a week. There are headache, nausea, vomiting, chill, fever, palpitation, bradycardia, heart block, respiratory distress, ankylosis, convulsions and delirium. In some cases, there may be aphonia and psychic depression. Death may occur. Ankylosis, peripheral neuritis and muscular atrophy are complications.

Treatment in cases of stinging by venomous fish

1. To relieve pain, analgesic is given.
2. Symptomatic treatment.
3. Steps to prevent secondary infection.
4. To attenuate the venom, hot compression with magnesium sulphate solution or plain hot water is helpful.
5. Antihistaminic cream locally, reduces reaction.


Poisoning occurs either by surface contact or when used as food.

By surface contact –

Here poisoning occurs due to injection of the venom by stinging cells of the invertebrate.

1. Jelly fish like Portuguese Man of War, Sea Anemone, Sea nettle, Sea Wasp, Sea Blubber and living Coral have long tentacles which have stinging cells which inject venom when come in contact with the skin. The venom contains 5-hydroxytryptamine and urocanyl- choline.
2. Molluscs or mussels, like conch shells, squid and octopus have highly developed venom apparatus which can cause punctures on the skin and then inject venom.
3. Sea urchins have venomous spines covering their body surface.
4. Bristle worm (stings with bristle).
5. Blood worm bites and injects toxic substance.

Signs and symptoms due to stinging or biting by poisonous invertebrates.

There is local reaction with pain, swelling and redness. In some cases there are nausea, vomiting, muscular cramps, paralysis, convulsion, collapse, respiratory distress and death.

Treatment – 1. Washing the part with mineral oil or alcohol or alkaline solution. 2. Use of pain killer. 3. Symptomatic treatment.

Poisoning due to eating of poisonous aquatic animals-

Consumption of California mussel, which eat planktons having deadly toxins, may cause sensory and motor disturbances like paresthesia, tingling, numbness, muscular weakness and paralysis.

Consumption of some shells, shrimps and crabs may cause chronic arsenic poisoning.

Consumption of puffer fish causes tetrodotoxin poisoning, leading to vomiting, retching, lethargy, muscular weakness, low B. P. and respiratory depression.

Treatment – Symptomatic.