Silke Arndt / Western rattlesnake (Crotalus viridis viridis), threat display, South Dakota, USA, September.

John Cancalosi / Western diamondback rattlesnake (Crotalus atrox), defensive rattling, Arizona, USA, April.

John Cancalosi / Group of gravid female Timber rattlesnakes (Crotalus horridus) basking before giving birth, Pennsylvania, USA, July.

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

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

Pete Oxford / Osborne's Lancehead (Bothrops osbornei) juvenile showing differently colored tail tip used for caudal luring, native to South America

Pete Oxford / Fer-de-lance (Bothrops asper), native to South America

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