The blue whale is the largest animal ever known, reaching substantially greater mass than any known dinosaur or other living species.
Blue whales are baleen whales, meaning they filter food from seawater rather than catching prey with teeth. Their main food is krill, which they engulf in huge mouthfuls of water and strain through overlapping baleen plates. During feeding, a blue whale can consume several tonnes of krill in a day.
The species occurs in oceans worldwide, although populations are divided into regional groups. Its long, streamlined body is usually blue-gray, often with lighter mottling. Despite its size, the blue whale feeds on tiny crustaceans rather than large fish or marine mammals.
Commercial whaling greatly reduced blue whale numbers during the twentieth century. International protection stopped most hunting, but the species remains endangered, with recovery varying among populations. A common mix-up is calling the whale shark the largest animal: the whale shark is the largest fish, while the blue whale is the largest animal overall.