John Cancalosi / Female Timber rattlesnake (Crotalus horridus) at nest site with newborn young, Pennsylvania, USA, September.

Tony Phelps / Puff adder (Bitis arietans) moving into ambush position under a bush, DeHoop Nature Reserve, Western Cape, South Africa, January.

Daniel Heuclin / Sunda island pitviper (Trimeresurus insularis) in tree, Komodo Island.

Bence Mate / Western diamond-backed rattlesnake (Crotalus atrox) Texas, USA, April.

Ingo Arndt / Prairie rattlesnake (Crotalus viridis viridis), threat display, South Dakota, USA September. Sequence 1 of 3

Bruno D'Amicis / Sand viper (Cerastes vipera) sidewinding on sand dunes. Grand Erg Oriental, Kebili Governorate. Tunisia.

Alex Hyde / Adder (Vipera berus) basking amongst bracken fronds. Peak District National Park, Derbyshire, UK. April.

Daniel Heuclin / Western diamondback rattlesnake (Crotalus atrox) tasting air, in habitat, Arizona, USA, October. Controlled conditions

Juergen Freund / Banded sea kraits (Laticauda colubrina) around the roots of mangrove tree, split level. Mali Island, Macuata Province, Fiji, South Pacific.

Chris Mattison / Sidewinder (Crotalus cerstastes) in sand dunes, Anza-Borrego Desert State Park, California, USA, May.

Daniel Heuclin / Mojave rattlesnake (Crotalus scutulatus) Mojave desert, California, June.

Daniel Heuclin / Rhinoceros viper (Bitis nasicornis), from Central Africa, captive, July.