Lucas Bustamante / Red tailed boa constrictor (Boa constrictor constrictor) juvenile, portrait, with tail wrapped round head, Cuayabeno, Sucumbios, Ecuador.

Ingo Arndt / Prairie Rattlesnake (Crotalus viridis viridis) in defensive posture, South Dakota

Chris Mattison,Chris Mattison / Rubber Boa (Charina bottae) in defensive posture, raising tail to mimic head. California, USA, November.

Daniel Heuclin / Great basin Gopher Snake / Bullsnake (Pituophis catenifer deserticola) head profile, controlled conditions, Joshua Tree National Monument, California USA

Sandesh Kadur / Large scaled pit viper (Trimeresurus macrolepis) head profile, water droplet below, Western Ghats, Southern India

Laurie Campbell / Male Adder (Vipera berus) basking on rock, Northumberland National Park, England, May

Pete Oxford / Eastern indigo snake (Drymarchon couperi) The Orianne Indigo Snake Preserve, Telfair County, Georgia, USA, threatened species, captive

John Cancalosi / Boa Constrictor (Boa constrictor) shedding skin from head. Guanacaste National Park, Costa Rican tropical rainforest.

John Cancalosi / Boa Constrictor (Boa constrictor) shedding skin from head. Guanacaste National Park, Costa Rican tropical rainforest.

Sven Zacek / Grass Snake (Natrix natrix) looking out from between wood slats. Estonia, Europe, June.

Klaus Echle / Black Viper / Adder (Vipera berus) head in profile. Black Forest, Germany, June.

Daniel Heuclin / White-lipped / Green tree viper (Cryptelytrops albolabris) captive, from SE Asia

Pete Oxford / Sipo Snake (Chironius exoletus) head against a white background. Captive. Endemic to Mindo Cloud Forest, Ecuador.

Juergen Freund / Researchers Guido and Katja Westhoff work in a mobile lab in the bush. To handle the deadly Common death adder (Acanthophis antarcticus) Guido puts the head and upper portion of the snake in a plastic...

Juergen Freund / Close-up of a Horned sea snake (Acalyptophis peronii) resting its head on its coils. Queensland, Australia, February

Danny Green / 2020VISION / Adder (Vipera berus) head portrait, Staffordshire, England, UK, April

Daniel Heuclin / Brown-banded Southern Water Snake (Nerodia fasciata) head in profile as it tastes the air with tongue. Controlled conditions. Lake Fausse-Pointe State Park, Louisiana, USA, November.

Solvin Zankl / Grass snake (Natrix natrix) head portrait flicking tongue

Bence Mate / Head portrait of Satiny Parrot snake (Leptophis depressirostris) swallowing frog, Hungary, Europe

Graham Eaton / Snake Pipefish (Entelurus aequoreus) head portrait in profile in weed, Cardigan Bay, Wales, May.

Rolf Nussbaumer / Western Cottonmouth snake (Agkistrodon piscivorus leucostoma) on lake flicking tongue. Fennessey Ranch, Refugio, Coastal Bend, Texas Coast, USA

Rolf Nussbaumer / Rough Green Snake (Opheodrys aestivus) head portrait, Refugio, Coastel Bend, Texas, USA

Rolf Nussbaumer / Head portrait of Gulf Coast Ribbon snake (Thamnophis proximus orarius) covered in duckweed and swimming, with tongue protruding, Fennessey Ranch, Refugio, Corpus Christi, Coastal Bend, Texas Coast, U...

Rolf Nussbaumer / Checkered Garter Snake (Thamnophis marcianus marcianus) coiled with tongue protruding. Fennessey Ranch, Refugio, Corpus Christi, Coastal Bend, Texas Coast, USA

Paul Hobson / Grass snake (Natrix natrix) swimming amongst duck weed, Oxfordshire, UK

Edwin Giesbers / Shed skin of grass snake {Natrix natrix} on lilypad, Netherlands.

Edwin Giesbers / Grass snake {Natrix natrix} coiled, the Netherlands

Edwin Giesbers / Copperhead snake {Agkistrodon contortrix} captive, from USA

Edwin Giesbers / Canebrake Rattlesnake {Crotalus horridus atricaudatus} captive;

Edwin Giesbers / Eastern green mamba {Dendroaspis angusticeps} head portrait, captive, from East Africa;

Edwin Giesbers / Eastern green mamba {Dendroaspis angusticeps} strike pose, captive, from East Africa

Wild Wonders of Europe / Ziegler / Balkan whip snake (Hierophis gemonensis) head portrait, The Peloponnese, Greece, May 2009

Andy Sands / Female Adder {Vipera berus} close up of head of snake, Sussex, England

Tony Phelps / Boomslang snake {Dispholidus ypus} male head raised, Western Cape, South Africa

Mary McDonald / Gaboon viper head close-up {Bitis gabonica} captive

Tim Fitzharris / Common Garter Snake (Thamnophis sirtalis) with extended tongue, very common snake, North America

Pete Oxford / Emerald Tree Boa (Corallus caninus) showing thermoreceptors between the labial scales, Amazon, Ecuador

Michael & Patricia Fogden / Common Egg-eating Snake (Dasypeltis scabra) swallowing egg from another animal's nest, savannah, South Africa

Michael & Patricia Fogden / Common Egg-eating Snake (Dasypeltis scabra) swallowing egg, Africa

Claus Meyer / Parrot Snake (Leptophis ahaetulla) with mouth open in defense display, Caatinga ecosystem, Brazil

Michael & Patricia Fogden / Russell's Viper (Daboia russelii) being milked for venom, Madras India

Michael & Patricia Fogden / Eyelash Viper (Bothriechis schlegelii) showing loreal pits for detecting heat, rainforest, Costa Rica

Michael & Patricia Fogden / Bushmaster (Lachesis muta) baby hatching from egg, lowland rainforest on Atlantic slope of Costa Rica

Heidi & Hans-Juergen Koch / Dione Rat Snake (Elaphe dione) beginning to shed its skin, native to Europe and Asia

Heidi & Hans-Juergen Koch / Colubrid Snake (Elaphe sp) two making initial contact, using tongue (Nasovomeral sense) to identify friend, enemy, or prey

Larry Minden / Red Rattlesnake (Crotalus ruber) coiled on ground, Baja California, Mexico

Larry Minden / Red Rattlesnake (Crotalus ruber) with tongue extended, Baja California, Mexico

Mike Wilkes / Head of Grass Snake in grass (Natrix natrix) UK

Andrew Cooper / Grass Snake head, England

Morley Read / Parrot snake (Leptophis ahaetulla), with a fly on its head, enters its mouth, Amazon rainforest, Orellana Province, Ecuador. (non-ex)

Peter Lewis / Snakes head fritillary (Fritillaria meleagris) flowering with Dandelions in meadow Cricklade, Wiltshire, England, UK, April.

David Hall / Crocodile snake eel (Brachysomophis henshawi), head sticking out of gravel. Pantar, Alor Archipelago, Indonesia.

David Hall / Many-eyed snake eel (Ophichthus polyophthalmus), head peering out of burrow. Pantar, Alor Archipelago, Indonesia; November, 2006.

Robert Valentic / Dahl's whip snake (Platyceps najadum) with head up, ready to strike. Kardamyli, Peloponnese, Greece. August.

Fabio Pupin / Meadow viper, (Vipera ursinii), close-up of head, Italy, July . Non-ex.

Gary Bell/ Oceanwide / Black-finned Snake Eel (Ophichthus melanochir) buried in sand, Great Barrier Reef, Queensland, Australia

Heather Angel / Snake's head fritillary (Fritillaria meleagris), view into flower with linear green nectaries. In cultivation, Surrey, England, UK. April.

Jeff Foott / Pacific Rattlesnake (Crotalus oreganus) in defensive posture, Carrizo Plain National Monument, California

Shane Gross / Head portrait of a Shaws seasnake (Lapemis curtus) underwater near Malapascua, Philippines.

Paul Hobson / Parrot snake (Leptophis ahaetulla) head, looking at camera. Costa Rica.

Donald M. Jones / Western Rattlesnake (Crotalus viridis) flicking tongue, Montana

Donald M. Jones / Western Rattlesnake (Crotalus viridis) in defensive posture, North America

Agustin Esmoris / South American Hognose Snake (Xenodon dorbignyi) flicking tongue, Buenos Aires, Argentina

Agustin Esmoris / South American Hognose Snake (Xenodon dorbignyi) flicking tongue, Buenos Aires, Argentina

Mike Read / Snakeshead fritillary (Fritillaria meleagris) growing in garden lawn. Corfe Mullen, Dorset, England, UK. April.

Ingo Arndt / Rhino Rat Snake (Rhynchophis boulengeri), native to Asia

David Fleetham / Freckled snake eel (Callechelys lutea) head poking out of sand with rest of body buried. Hawaii.

Andrew Snyder / Rainbow boa (Epicrates cenchria showing iridescence on head, Iwokrama, Guyana.

Tony Wu / Snake eel (Ophisurus macrorhynchos) waiting to ambush prey, head poking out of sand. Sue, Wakayama Prefecture, Kansai, Honshu, Japan. February.

Adrian Davies / Snakeshead fritillary (Fritillaria meleagris), rare double white variety. Beech Hill, Berkshire, England, UK. April.

Jen Guyton / Mopane snake (Hemirhagerrhis nototaenia), from the Greater Gorongosa Ecosystem, Mozambique. Here, the snake shows its defensive tail display -- the contrastingly colored orange tail is held up to dist...

Daniel Heuclin / Royal python (Python regius) female with ticks on the side of her head, incubating eggs, Togo. Controlled conditions

Daniel Heuclin / Calabar burrowing boa snake (Calabaria reinhardtii) in defensive ball, captive, occurs equatorial rain forest of West and central Africa. Head and tail are very similar

Daniel Heuclin / Calabar burrowing boa snake (Calabaria reinhardtii) in defensive ball, captive, occurs equatorial rain forest of West and central Africa. Head and tail are very similar

Daniel Heuclin / Calabar burrowing boa snake (Calabaria reinhardtii) in defensive ball, captive, occurs equatorial rain forest of West and central Africa. Head and tail are very similar

Daniel Heuclin / Calabar burrowing boa snake (Calabaria reinhardtii) in defensive ball, captive, occurs equatorial rain forest of West and central Africa. Head and tail are very similar

Daniel Heuclin / Calabar burrowing boa snake (Calabaria reinhardtii) in defensive ball, captive, occurs equatorial rain forest of West and central Africa. Head and tail are very similar

Lucas Bustamante / Ecuadorian toadhead (Bothrocophias campbelli) with Mosquito (Culicidae) feeding on its head, Mindo, Pichincha, Ecuador.

Lucas Bustamante / Black Mamba (Dendroaspis polylepis) lifting up head, Moremi Game Reserve, Botswana.

Paul Bertner / Snake (Lamprophiidae), Ranomafana National Park, Madagascar

Paul Bertner / Blunthead Slug Snake (Aplopeltura boa) flicking tongue, Bukit Barisan Selatan National Park, Sumatra, Indonesia

Paul Bertner / Big-eyed Bamboo Viper (Trimeresurus macrops), Virachey National Park, Cambodia

Paul Bertner / Oriental Whip Snake (Ahaetulla prasina) flicking tongue, Cuc Phuong National Park, Vietnam

Paul Bertner / Oriental Whip Snake (Ahaetulla prasina), Mount Isarog National Park, Philippines

Paul Bertner / Green-striped Vine Snake (Philodryas argentea), Yasuni National Park, Ecuador

Chris Mattison / Snakeshead Fritillary (Fritillaria meleagris) Monmouthshire, Wales, UK. March.

Thomas Marent / Aruba Rattlesnake (Crotalus durissus) fangs, native to South America

Javier Aznar / Sahara Sand Viper (Cerastes vipera) waiting to ambush prey at night, half buried under sand with only the head visible, Western Sahara Desert.

Javier Aznar / Sahara Sand Viper (Cerastes vipera) waiting to ambush prey at night, half buried under sand with only the head visible, Western Sahara Desert.

Ann & Steve Toon / Wildlife Trust volunteers surveying Snakeshead fritillary (Fritillaria meleagris) flowers. Iffley Meadow, Oxford. April.

Ann & Steve Toon / Snakeshead fritillary (Fritillaria meleagris) flower, Iffley Meadow, Oxford, April

Ann & Steve Toon / Snakeshead fritillaries (Fritillaria meleagris) in Iffley Meadow, Oxford. April.

Yashpal Rathore / King cobra (Ophiophagus Hannah) with head raised, Agumbe, Karnataka, India. Venomous species.

Loic Poidevin / Snake's head fritillary (Fritillaria meleagris) flowering in marsh, Audubon Reserve, West France, France, March

Mark Carwardine / Santa Catalina Rattlesnake (Crotalus catalinensis) flicking tongue, Santa Catalina Island, Baja California, Mexico

Pascal Kobeh / Bonapart's / Napoleon snake eel (Ophichthus bonaparti) head sticking out of sand, Sulu Sea, Philippines