SCIENCE REPORTER, April 201028

Feature Article

THINK venom and you cannot help thinking ofsnakes. But there are innumerable other species ofanimals equally capable of spewing venom anddealing a lethal blow.

Originating from the Latin word Venenem meaningpoison, venom can be defined as a zootoxin or a variety ofpoisonous substance secreted by an animal, produced byspecialized glands and associated with spines, tooth or stings.It may primarily be used for killing prey or may be defensiveor may even function as a digestive fluid. The venom maycause localized skin inflammation or almost instant death.

But is there any difference between venomous andpoisonous animals? Or are they both the same? Well, whilevenomous animals deliver or inject venom into their preyeither while hunting or while defending themselves,poisonous animals are harmful when consumed or touched.Venom is generally produced in organs specialized for thepurpose whereas poison is generally distributed over alarger part of the body of organisms producing it.

Now let’s take a look at some of these venomousanimals that could be equally poisonous as snakes.

Fatal FishesVenomous fishes outnumber not only venomous snakes butalso other venomous vertebrates put together. There aremore than 1200 species of venomous fishes occupying almostall aquatic ecosystems. Such fishes possess venom-producing glands and have mechanisms like sharp spinesfor inflicting the venom. Generally used for defence againstpredators, venom produced by a fish is often referred to asan ichthyotoxin whereas poison in the fish body is knownas ichthyosarcotoxin.

Chondrichthyes or cartilaginous fishes (havingcartilaginous skeletons) have a highly specialized anddangerous integumentary venom delivery apparatus – thespine or sting. These deciduous spines have grooves for toxicsecretions from contiguous glands, producing agonizingwounds that may result in septicemia and even death.

The stinger of a stingray is razor sharp, barbed, orserrated cartilaginous spine that grows from the ray’s whip

like tail as a fingernail. On the underside of the spine aretwo grooves containing the venom secreting glandulartissue. The entire spine is covered with a thin layer of skincalled the integumentary sheath in which the venom isconcentrated. The venom causes necrosis and tissuebreakdown.

Its venom causes punctures, poisoning, severed arteriesand even death. Treatment is with scalding water, antibioticsand local anesthetics. The naturalist, conservationist andadventurer, Steve Irwin, better known as the “Crocodilehunter”, was mortally wounded on 4 September 2006 by astingray while diving off the north Queensland coast duringthe filming of a documentary called The Ocean’ s Deadliest. Agiant bull stingray pierced his heart with a poisonous barb.Keeping a respectful distance and wearing ballistic nylonvest could have prevented his death.

However dangerous the stingray may be, in the CaymanIslands there is a stingray city where divers can swim withlarge Bat rays and feed them by hand. The Baltimoreaquarium has a large stingray tank where they may beviewed from above or below.

A large number of bony fishes are also known to bevenomous. Catfishes can cause painful wounds. FreshwaterNoturus have venom glands on the pectoral spines. Marinestriped eel catfish Plotosus lineatus has highly venomousserrated spine on the first dorsal fin and each of the pectoralfins. These may be fatal.

Toadfishes like Thalassophryne maculosa and Opsanus tauare ugly short-bodied fish with dorsally placed eyes on head.The dorsal fins and opercular spines are hollow and caninject venom that causes intense pain. Similarly, lightcolored, brown spotted Weever fish of family Trachinidaefound in coastal waters of any temperate sea has a row ofspines along its back. It buries itself under the sand waitingfor its prey. Venom of the fish is as powerful as the venomof the rattlesnake. It destroys Red Blood Cells and paralysesnerves. Burning pain lasts from thirty minutes to an hour.This intense pain can cause unconsciousness and lead todrowning of the victim. Aspivenin is very effective intreating poisonous fish stings.

Surgeonfishes of the family Acanthuridae have verysharp scalpel like spines protruding from the junction oftheir body and tail. Inhabiting mainly Indo-Pacific and

Lethal, venomous vertebrates occupy an important niche in the ecosystem.Although their venom could even be fatal, some venoms have proved to be

very important as pharmacological and biomedical compounds.

Spewing Venom!SAGARIKA CHAUDHURI

SCIENCE REPORTER, April 2010 29

Feature Articlesometimes the Atlantic Ocean, these beautifully colored andcompressed bodied fishes are poisonous. Ciguaterapoisoning is reported on consumption of surgeonfishes.Similarly, Scorpionfishes also possess venomous spines. TheZebra Turky fish Dendrochirus zebra of Indian and westernPacific oceans has 13 venomous spines along its back asdefensive organs.

Then there are Antennata Lion fish that have venomousspines fatal to their prey, though not fatal to humans. But itcauses severe pain, headaches and vomiting. Clear finLionfish Pterois radiata or Tail bar Lionfish inhabiting theIndian and Western Pacific oceans has venomous spines.The Red Lionfish Pterois volitaus inhabiting Indian andWestern Pacific oceans also possess venomous spines.

Stonefishes are the most venomous fishes known. Venomfrom the Reef Stonefish Synanceia verrucosa causes severe painwith possible shock, paralysis and tissue death dependingon the depth of penetration. The ugly looking Red seastonefish Synanceia nana also has venomous dorsal spines.

The blood, liver, gut and gonads of Puffer fishes containa virulent toxin capable killing humans. On contamination,it produces severe gastric disorder. In spite of the toxicity,puffer fishes are a delicacy in Japan and are called Fugu.Porcupine fish, Cowfish, Boxfish, Tobies and Sunfish areequally toxic. These fishes ingest algae covered with bacteriaAlteromonas that is the source of the toxin. This toxinconcentrates in the liver and gonads inhibiting sodiumtransport thus affecting neuronal transmission in the CNSand also affects cardiac nerve conduction and contraction.

Coral reef fishes such as barracuda, grouper andsnapper cause a very common toxicity, known as Ciguatera.

C i g u a t e r ap o i s o n i n gresults from theeating of reeffish affectedwith ciguatoxin.Dinoflagellates(Gambierdiscust o x i c u s )colonizing thecoral beds areresponsible forthe ciguatoxin.The toxin first affects the coral grazing fish and then ispassed through the food chain to fish feeding on them likesnapper, grouper, and amber jack and finally human beings.The toxin is not affected either by cooking or freezing.Intense itching, joint and muscular pain, tingling of thelips, gastrointestinal complaints are some of the symptomsof the poisoning. Ciguatoxin acts on the sodium channelsthereby causing changes in the electrical potential andpermeability.

Some popular aquarium fishes like longhorn Cowfish(Lactoria comuta) or cube box fish Ostracion cubicus and thePacific box fish O. melegris release a toxin called ostracitoxininto the water if they are alarmed. Due to space limitationin aquarium, this toxin has deleterious effect on otherfishes. Twenty-one species of the genus Takifugu containtetradotoxin. Intestines, liver and ovaries of the tiger puffer,skin and internal organs of smooth puffers and gut andmuscles of the green puffers are very toxic.

1

Red Lion fish

2

3 4

1. Sting ray;

2. Antennata Lion fish;

3. Stone fish ;

4. Zebra Turkey fish

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Feature Article

Abhorrent AmphibiansPoison glands of amphibians are located in the dermis andopen to the surface through connecting ducts. They generallycontain stored secretions in the lumen, which are a widevariety of irritating as well as toxic compounds. These toxicsecretions are potentially harmful only if eaten or injected.Poison glands in amphibians behave primarily as chemicaldefence systems and their locations are such that predatorsare exposed to them.

The European salamander (Pleurodeles waltl) and twogenera of Asian salamanders Echinotriton and Tylotriton possessribs that pierce the body wall when attacked by predators.These ribs penetrate poison glands while emerging throughthe body wall and eventually carry poison drops at the tip. Thered eft salamander Notopthalmus viridesceus and red salamanderPseudodotriton ruber have skin toxins – the tetrodotoxin – whichis a potent neurotoxin. Predators who have once experiencedthis toxin refuse to attack an eft in future.

The large crested or warty Newt Triturus cristatus ofEurope if attacked discharges a venomous secretion from itsdorsal glands. Most of the toads and salamanders possesssmall poison glands aggregated together as a prominentswelling. These are parotid glands and are located on eachside of the head. The Natterjacks have similar glands on eachhind leg. The large and prominent dorsal warts of toads are

Toad fish

Clear fin lion fish

Striped eel cat fish

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Feature Article

perforated by a pore that leads to a prominent gland beneath,capable of ejecting poison. The exudate contains two otheractive toxins, bufotalin and bufogin. If swallowed these causenausea, respiratory and muscular impairment and digitalislike action on heart.

Colorado river toads and cave toads have bufotoxins intheir skin secretions. These are psychoactive and are used asrecreational drugs. The poison dart frogs of the new worldtropics have large numbers of cutaneous alkaloids. SouthAmerican Indians use the toxins of some of these frogs topoison the tips of the blowgun darts used for hunting.Batrachotoxin, a unique alkaloid found in Phyllobates, is apotent neurotoxin. About 1900 micrograms of batrachotoxinis available from a single frog. Less than 200 micrograms is alethal dose for a human if it enters the body through a cut. Itprevents the closing of sodium channels in nerve and musclecells, leading to irreversible depolarization producing cardiacarrhythmia, fibrillation and cardiac failure.

Frog toxin isolated from another poison dart frogEpipedobates tricolor contains an anesthetic that acts as apainkiller 200 times more potent than morphine. This makesit of tremendous interest as a potential drug lead.

Rancorous ReptilesHollow fangs connected with poison glands are found invenomous lizards. The beaded lizard and the Gila monsterare the only venomous lizards with an overt venomdelivery system.

The beaded lizard is found in the Pacific Drainages fromsouthern Sonora to southwestern Guatemala and two Atlanticdrainages from central Chiapas to Southeastern Guatemala.Its venom glands are modified salivary glands located in theanimal’s lower jaw. Each gland is with a separate duct thatleads to the base of its grooved teeth. This lizard hangs on toits victim and chews so that the venomous saliva enters thewound. Although the jaw grip is strong, the unsocketed teethof the animal come out from their bases.

Their venom is a weak hemotoxin and consists of L-amino acid oxidase, hyaluronidase, phospholipase A,serotonin and highly active kallikreins that releasevasoactive kinins. The venom contains no enzymes thatsignificantly affect coagulation. Although human deaths arerare, the venom can cause respiratory failure. Excruciatingpain that may last for 24 hours, swelling of the affected part,rapid fall in blood pressure are other effects of the bite. Inother smaller mammals such as rats the bite may causeseveral cardiac anomalies, hypothermia, edema and internalhemorrhages. The compounds found in the venomous salivaare said to have pharmacological value in diabetes,Alzheimer’s disease and even HIV.

Gila monster (Heloderma suspectum) is the inhabitant ofthe deserts of southwestern USA and northwestern Mexico.Venom is produced in modified salivary glands of the lowerjaws of the Gila monster quite unlike that of snakes wherevenom is produced in the upper jaws. The Gila monsterlacks the musculature to forcibly inject the venom; insteadthe venom is propelled from the gland to the tooth. Bychewing, the capillary action brings the venom out of thetooth and into the victim. While biting the animal flips overpossibly to aid the flow of venom. Since victims of this animalare always helpless prey, it is thought that Gila monster’svenom evolved for defensive rather than for hunting.

The venom of Gila monster is neurotoxic and as toxicas the western diamond back rattlesnake. This monster canbite in quick succession and can hold on ferociously. Thoughnot fatal tohumans it cancause excruciatingpain, edema andw e a k n e s sassociated with fallin blood pressure.

More than adozen peptidesand proteins havebeen isolated fromthe Gila monster’sv e n o m .Hyaluronidase ,s e r o t o n i n ,phospholipase A2and severalkallikrein likeglycoproteins areresponsible for thepain and edemacaused by the bite.Four potentiallylethal toxins arealso isolated fromthe venom.

Venomous SnakesRecent DNA analysis suggests that the closest relatives ofsnakes are iguanas and the two venomous lizards. Venomoussnakes and lizards shared a common ancestor 200 millionyears ago. Considered the most dreadful of all animals thatcohabit our planet, 750 species are venomous out of 3000 ormore species of existing snakes. About 250 species areregarded as dangerous to humans and only 50 or so are

Mexican Beaded lizard (top) and Gila Monster (above)

From Left: Blow fish ; Puffer fish; Poison dart frogs- Epipedobates tricolor; Dendrobates azureus; Dendrobates tinctorius

SCIENCE REPORTER, April 201032

Feature Articlepotentially lethal. Though recent findings reveal that morethan 2000 species of snakes possess venom and all snakesmay be venomous to a certain extent even if the venom issmaller in quantity and is delivered through sharp teethrather than fangs. There are over 270 species of snakes inIndia out of which about 60 are venomous.

A venomous snake uses modified saliva as the venom,which is usually delivered through highly specialized teethsuch as hollow fangs. In contrast non-venomous specieseither constrict their prey or simply overpower them withtheir jaws.

There are four families of venomous snakes:� Atractaspididae comprising burrowing asps, mole

vipers, stiletto snakes found in Africa and Middle Eastand comprise fang-less (aglyphous), rear fanged(opisthoglyphous), fixed fanged (proteroglyphous) andviper-like (solenoglyphous) species.

� Colubridae comprising mostly harmless snakes, butsome have toxic saliva and at least five species includingthe Boomslang have caused human fatalities. A fewgroups of the genus Boiga can produce medicallysignificant bites. In venom producing colubrids thefangs are situated in the back of the mouth.

� Elapidae or elapids are the family of venomous snakesfound in the tropical and sub tropical regions aroundthe world including the Indian Ocean and Pacific. Thereare more than 60 genera and 230 species comprisingCobras, Coral snakes, Kraits, Mambas, Sea snakes, SeaKraits and Australian elapids. They possess hollow andfixed fangs to inject venom.

� Viperidae or vipers comprise pit vipers (with heatsensing pits) as rattlesnakes and moccasins and suchtrue or pitless vipers as puff adders.

Out of a number of venomous snakes in India the mostfamous are the Big Four: Saw scaled viper, Russell’s viper,Krait and the Indian Cobra.

Saw scaled viper (Echis carinatus) has highly virulenthemotoxic venom and it produces a sharp sizzling soundby rubbing the body sides together. Russell’s Vper (Daboisrusselii) is a large snake with large triangular head and largefangs producing a low rasping sound by rubbing its scalestogether. The Krait (Bungarus caeruleus) has bold stripedpatterns of alternating black and light colored area. Theirneurotoxic venom is 16 times stronger than cobra venom.Indian Cobra or Spectacled Cobra (Naja naja) is the mostfamous of the big four. Its venom contains a powerfulpostsynaptic neurotoxin. King cobra (Ophiophagus hannah)is anther famous snake that can discharge venom equal to10 lethal doses to a man in one bite.

Venom is highly modified saliva that is produced byspecial glands. Like all salivary secretions venom is a pre-digestant that initiates the breakdown of food into solublecompounds allowing for proper digestion. It is a complexmixture of proteins such as neurotoxins, hemotoxins,cytotoxins, bungarotoxins and enzymes meant originallyfor digestion of the prey. The stronger these digestive juices,the more powerful the venom. Almost all snake venomcontains hyaluronidase an enzyme that ensures rapiddiffusion of the venom.

These prey-immobilizing substances in snakes arecomposed of approximately 90% proteins. Some of theenzymes present in snake venom are phosphodiesterasesinterfering with the prey’s cardiac system, mainly to lowerthe blood pressure; cholinesterase inhibitor making preyto loose muscle control; and hyalorunidase, increasing tissuepermeability to increase the rate of absorption of enzymesinto the prey’s tissue.

A. Saw scaled Viper

B. Krait

C. Binocellate or common Cobra

D. Snake charming

E. Cobra in captivity

A

E

D B C

SCIENCE REPORTER, April 2010 33

Venom of Cobras and Coral snakes also has neurotoxinsor nerve toxins that attack the victim’s central nervoussystem and brain. This may result in heart failure, breathingdifficulties or even total respiratory paralysis. The venomof the viper is hemotoxic or a blood toxin that affects theheart, cardiovascular system and muscle tissue resulting inexcessive scurrying and gangrene. This may lead toamputation of the affected area. The toxin destroys the tissueand blood cells ultimately killing the prey. The venom ofkrait acts both as neurotoxin and hemotoxin. Primarysymptoms like severe abdominal pain, dribbling of salivaetc. occur. Death results from asphyxia through paralysis ofthe respiratory centre.

The most potent venom is produced by those snakesthat feed on fast-moving prey. Many venomous snakes haveprey-specialised venom. The venom of some marinehydrophis (elapids) is among the most toxic in the world.The reason is that these snakes consume reef fish that wouldelude them if the venom did not act rapidly. The Australianinland taipan, the black mamba and the king cobra areconsidered to be the most venomous. But they are rare andnot very aggressive and so they kill few people. Asiaticcobras, Russel’s vipers and saw-scaled vipers have less toxicvenom, but kill about 100,000 people a year.

Poisonous BirdsA few poisonous birds are also known. They do not producevenom themselves but acquire poisons from their diet.These toxins probably serve the birds as chemical defense,either against ecto parasites or against predators such assnakes, raptors or humans. Birds of the genus Pitohuibelonging to the family Pachycephalidae, endemic to NewGuinea, have brightly coloured skin and feathers whichcontain powerful neurotoxin alkaloids of the batrachotoxingroup. This toxin is a neurotoxin called homobatrachotoxinthat causes numbness and tingling in those touching thebird. The poison is acquired by eating the choresine beetle.It is probably the same beetle that is the source of lethalbatrachotoxin in poison dart frogs.

Some species of these Pitohui birds are Hooded Pitohui(Pitohui dichrous); Variable Pitohui (Pitohui kirhocephalus);Blue capped Ifrita (Ifrita kowaldi), and Rufous or little Shrikethrush (Colluricincla megarhyncha).

Malicious MammalsA very few mammals also produce venom either to kill orto disable prey to defend themselves. Venom delivery is arare phenomenon in the class Mammalia and the reasonaccording to scientists is that modern and smart mammals

Feature Article

Platypus; Solenodon and Great long nosed ArmadilloH. pitohui (left)

Rufous Shrike Thrush rather use tooth or claw than venom,which takes longer time to disable prey.Some such mammals are:

Platypus or the Duckbill (Ornithorhynchusanatinus) is endemic to western Australia andTasmania. Males have sharp, movable, fang-like half-inch-long spur on the inner side of the ankle of the hind limbs.This is connected with a small crural gland having poisonousalbuminous secretion, capable of killing a rabbit in 90 seconds.This venom if injected causes severe pain in humans. Thoughnot lethal, it is so excruciating that the victim may beincapacitated. Oedema develops around the wound, whichspreads throughout the affected limbs. Of the four majortoxins present in its venom, three cause lowering of bloodpressure, pain and increasing blood flow around the wound.It is powerful enough to seriously impair the victim.

The males of Spiny anteater (Tachyglossus = Echidna)possess the poison spur on the leg supplied by a pea-sizedgland. Similarly, Short-tailed shrew (Blarina brevicauda),Southern short-tailed shrew (Blarina carolinensis), Elliot’s short-tailed shrew (Blarina hylophaga), Northern short-tailed shrew(B. brevicauda) and Eurasian water shrew (Neomys fodieus)deliver a venomous bite that can immobilize larger animals.

Solenodon is the only living mammal species that isable to inject venom through specially modified teeth justlike snake. Solenodons are often referred to as living fossilsas they constitute an ancient mammal lineage. There aretwo species of Solenodons—Haitian Solenodon (Solenodonparadoxus) and Cuban Solenodon (Solenodon cubanus). TheseSolenodons look like large shrews and their venom isdelivered from modified salivary glands via grooves intheir second lower incisors.

Slow Loris – Sunda Loris (Nycticebus coucang), Bengalslow Loris (N. bengalensis) and Pygmy slow Loris (N. pygmeus)secrete toxins used for covering their babies in order toprotect them from predators. Toxins are secreted from glandssituated inside their elbows.

Striped skunk (Mephitis mephitis) and American skunk(Conepatus leuconotus) can eject a strong foul-smellingnoxious fluid from glands situated near their anus. This cancause irritation and even temporary blindness in the eyes.

Some of the other venomous mammals are Striped Polecat (Ictonyx sriatus), which excretes a strong foul-smellingodour; Sunda pangolin (Manis javanica) or the Scaly anteater,which emits a noxious smelling fluid, and Great Long nosedArmadillo, which has spurs on hind legs that can inflictdamage to humans.

Dr. Sagarika Chaudhuri is Reader in Zoology, Sree Chaitanya College, Habra,West Bengal. Address: G-3, Staff Quarters, Jadavpur University, Kolkata-700032; Email: sagarikachaudhuri@yahoo.com.