Crotalinae
Pit vipers range in size from the hump-nosed viper, Hypnale hypnale, which grows to around 30–45 centimetres (12–18 in), to the South American bushmaster, Lachesis muta, which grows to 3.65 metres (12.0 ft). This is the longest venomous snake in the New World. Some pit vipers are arboreal (they live in trees), some are terrestrial, and one species is semi-aquatic: the cottonmouth, Agkistrodon piscivorus.