Daniel Heuclin / Asp viper (Vipera aspis) with head held in hand, and mouth open to show venomous fangs. France, Europe. Controlled conditions.

Daniel Heuclin / Asp viper (Vipera aspis) captured, and having chip inserted, by a researcher. France, Europe.

Michael D. Kern / African bush viper (Atheris squamigera) captive, from Africa

Michael D. Kern / Usambara bush viper (Atheris cerataphora) captive, from Tanzania

Michael D. Kern / Beautiful Pit Viper (Trimeresurus venustus) body held up in coils, captive, from Asia

Michael D. Kern / Usambara bush viper (Atheris cerataphora) captive, from Tanzania

Michael D. Kern / African bush viper (Atheris squamigera)

Michael D. Kern / Eyelash viper (Bothriechis / Bothrops supraciliaris) captive, from South america

Michael D. Kern / Mangrove viper (Cryptelytrops purpureomaculatus) captive, from Asia

Michael D. Kern / Guatemalan palm viper (Bothriechis aurifer) captive, from South America

Michael D. Kern / Two Stejneger's bamboo pitviper (Trimeresurus / viridovipera stejnegeri) captive from Asia

Michael D. Kern / Eyelash viper (Bothriechis / Bothrops schlegelii) captive, from Central and South America

Michael D. Kern / Eyelash viper (Bothriechis / Bothrops schlegelii) captive, from Central and South America

Michael D. Kern / Rhinoceros viper (Bitis nasicornis) captive, from Africa

Michael D. Kern / Rhinoceros viper (Bitis nasicornis) captive, from Africa

Michael D. Kern / Temple / Wagler's pit viper (Tropidolaemus wagleri) captive, from Asia

Michael D. Kern / Lataste's viper (Vipera latastei gaditana) captive, from SW Europe

Michael D. Kern / Egyptian saw scaled viper (Echis pyramidum) captive, from N Africa

Michael D. Kern / Vogel's pit viper (Viridovipera / Trimeresurus vogeli) captive, from SE Asia

Michael D. Kern / Desert horned viper (Cerastes cerastes) captive, from N Africa and Middle East

Michael D. Kern / Lansbergi pitviper (Porthidium lansbergii rozei) captive, from Central and South America

Michael D. Kern / Gaboon viper (Bitis gabonica) captive, from Africa

Michael D. Kern / Gaboon viper (Bitis gabonica) showing cryptic markings, captive, from Africa

Michael D. Kern / Gaboon viper (Bitis gabonica) showing cryptic markings, captive, from Africa

Michael D. Kern / Gaboon viper (Bitis gabonica) with tongue exposed, captive, from Africa

Michael D. Kern / McMahons desert viper (Eristicophis macmahoni) sinking into sand, captive, from Asia

Michael D. Kern / McMahons desert viper (Eristicophis macmahoni) sinking into sand, captive, from Asia

Michael D. Kern / Olmecan pit viper (Atropoides olmec) captive, from central America

Michael D. Kern / Wagler's / Temple pit viper (Tropidolaemus subannulatus) captive, from Asia

Michael D. Kern / Wagler's / Temple pit viper (Tropidolaemus subannulatus) captive, from Asia

Michael D. Kern / Mangrove pitviper (Cryptelytrops purpureomaculatus) captive, from Asia

Michael D. Kern / Eyelash palm viper (Bothriechis / Bothrops schlegelii) captive, from Central and South America

Michael D. Kern / Usambara bush viper (Viperatheris ceratophora) captive, from Tanzania

Michael D. Kern / African / Variable bush viper (Atheris squamiger) captive, from Africa

Michael D. Kern / Temple / Wagler's pit viper (Tropidolaemus subannulatus) captive, from Asia

Michael D. Kern / Radde's / Armenian mountain viper (Vipera raddei) captive, from Middle east and Armenia

Michael D. Kern / Banded pit viper (Cryptelytrops fasciatus) captive, from Asia

Michael D. Kern / Elegant pitviper (Protobothrops elegans) captive, from Japan

Michael D. Kern / Temple pit viper (Tropidolaemus subannulatus) captive, from SE Asia

Michael D. Kern / Temple pit viper (Tropidolaemus subannulatus) captive, showing forked tongue, from se Asia

James Christensen / Eyelash Viper (Bothriechis schlegelii) juvenile on mossy tree, Mindo, Ecuador

James Christensen / Eyelash Viper (Bothriechis schlegelii) juvenile on mossy tree, Mindo, Ecuador

James Christensen / Eyelash Viper (Bothriechis schlegelii) juvenile on mossy tree, Mindo, Ecuador

Murray Cooper / Rainforest Hognose Viper (Porthidium nasutum) coiled on tree trunk, Ecuador

Richard Herrmann / Southern Pacific Rattlesnake (Crotalus viridis helleri) in defensive position, Poway, California

Pete Oxford / Eastern Diamondback Rattlesnake (Crotalus adamanteus) showing 'blue eye' indicating animal is about to molt, Little St. Simon's Island, Georgia

Pete Oxford / Eastern Diamondback Rattlesnake (Crotalus adamanteus) showing 'blue eye' indicating animal is about to molt, Little St. Simon's Island, Georgia

Pete Oxford / Eastern Diamondback Rattlesnake (Crotalus adamanteus) with extended tongue, Little St. Simon's Island, Georgia

Pete Oxford / Eastern Diamondback Rattlesnake (Crotalus adamanteus) showing rattle, Little St. Simon's Island, Georgia

Pete Oxford / Eastern Diamondback Rattlesnake (Crotalus adamanteus) coiled in leaf litter, Little St. Simon's Island, Georgia

Luciano Candisani / Aruba Rattlesnake (Crotalus durissus) in scrub habitat, Jalapao State Park, Jalapao, Brazil

James Brickell / Gaboon viper (Bitis gabonica) camouflaged against leaf litter, Mpumalanga, South Africa

Dietmar Nill / Sand viper (Vipera ammodytes) Germany

Edwin Giesbers / Rhinoceros viper / adder {Bitis nasicornis} close up of eye, captive, from Africa;

Edwin Giesbers / Asp viper {Vipera aspis} captive, from southern europe

Edwin Giesbers / Horned viper {Cerastes cerastes} head portrait, captive, from Africa

Edwin Giesbers / Rhinoceros viper / adder {Bitis nasicornis} skin detail, captive, from Africa

Edwin Giesbers / Horned viper {Cerastes cerastes} moving through sand, captive, from Africa

Edwin Giesbers / Horned viper {Cerastes cerastes} camouflaged in sand, captive, from Africa

Edwin Giesbers / Rhinoceros viper / adder {Bitis nasicornis} skin detail, captive, from Africa

Edwin Giesbers / Rhinoceros Viper / adder {Bitis nasicornis} skin patterns, captive, from Africa

Edwin Giesbers / Gaboon viper {Bitis gabonica} head portrait, captive, from Eastern and Central Africa;

Edwin Giesbers / Sand / European Horned Viper {Vipera ammodytes} captive, from eastern Europe, Europe's most dangerous snake;

Edwin Giesbers / Gaboon viper {Bitis gabonica} skin detail, captive, from Eastern and Central Africa;

Edwin Giesbers / Gaboon viper {Bitis gabonica} head portrait, captive, from Eastern and Central Africa;

Edwin Giesbers / Gaboon viper {Bitis gabonica} close up of eyes, captive, from Eastern and Central Africa;

Edwin Giesbers / Gaboon viper {Bitis gabonica} head portrait, captive, from Eastern and Central Africa;

Edwin Giesbers / Jumping Viper {Atropoides / Bothrops nummifer} head detail, Captive, from Central America

Edwin Giesbers / Lowland Swamp Viper {Proatheris superciliaris} captive, from swampy grasslands of SE Africa;

Edwin Giesbers / Rhinoceros viper / adder {Bitis nasicornis} showing camouflage nature of skin pattern, captive, from Africa

Edwin Giesbers / Rhinoceros viper / adder {Bitis nasicornis} captive, from Africa

Edwin Giesbers / Rhinoceros viper / adder {Bitis nasicornis} head portrait, captive, from Africa

Chien Lee / Borneo Keeled Pit Viper (Tropidolaemus subannulatus) with extended tongue, Kubah National Park, Borneo, Malaysia

Wild Wonders of Europe / Maitland / Black veined white butterfly (Aporia crataegi) feeding on Viper's bugloss (Echium vulgare) Lagadin region, Lake Ohrid, Galicica National Park, Macedonia, June 2009

Claudio Contreras / Rainforest hognose pitviper (Porthidium nasutum) Montes Azules Biosphere Reserve, Lacandon Rainforest, Mexico, September

Claudio Contreras / Rainforest hognose pitviper (Porthidium nasutum) Montes Azules Biosphere Reserve, Lacandon Rainforest, Mexico, September

Albert Lleal / Western Diamondback Rattlesnake (Crotalus atrox) albino smelling the air with his tongue, native to North America

Albert Lleal / Western Diamondback Rattlesnake (Crotalus atrox) retracting and repositioning fangs, native to North America

Stephen Dalton / Rhinoceros viper {Bitis nasicornis} close up showing head and horns

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra), Tapichalaca Reserve, Ecuador

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra) on bromeliad, Tapichalaca Reserve, Ecuador

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra) profile showing heat-sensing pit organ, Tapichalaca Reserve, Ecuador

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra) coiled on a bromeliad, Tapichalaca Reserve, Ecuador

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra) coiled in the center of a bromeliad, Tapichalaca Reserve, Ecuador

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra) with extended tongue, Tapichalaca Reserve, Ecuador

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra) with extended tongue, Tapichalaca Reserve, Ecuador

Nigel Marven / Orsinii's viper (Vipera ursinii) on rock with flowers, Albarz Mountains, Iran, vulnerable species

Wild Wonders of Europe / Wothe / Viper's bugloss (Echium vulgare) in flower, East Slovakia, Europe, June 2008

Wild Wonders of Europe / Wothe / Viper's bugloss (Echium vulgare) in flower, East Slovakia, Europe, June 2008

James Christensen / Ecuadorian Toad-headed Pit-viper (Bothrocophias campbelli), Andes, Ecuador

James Christensen / Ecuadorian Toad-headed Pit-viper (Bothrocophias campbelli), Andes, Ecuador

James Christensen / Ecuadorian Toad-headed Pit-viper (Bothrocophias campbelli), Andes, Ecuador

James Christensen / Ecuadorian Toad-headed Pit-viper (Bothrocophias campbelli), Andes, Ecuador

James Christensen / Ecuadorian Toad-headed Pit-viper (Bothrocophias campbelli), Andes, Ecuador