A blue poison frog (Dendrobates azureus) sits on a branch in the zoo of Zurich, March 22,2006. The blue colour of this South-American frog serves as a warning to would-be predators, its skin is covered with glands that secrete alkaloid poisons capable of paralyzing and even killing predators. With the destruction of its rainforest habitat the blue poison frog has become one of the most threatened of all poison dart frogs. REUTERS/Siggi Bucher