Blue whale, worldwide, up to 30 m (100 ft) long The blue whale is a rorqual, a group of baleen whales that includes the Bryde's, humpback, fin, minke and sei whales. The largest living animal on Earth—probably the largest animal that has ever lived—the blue can grow up to 30 metres (100 feet) long and weigh 170 tonnes or more. However, this huge creature feeds mostly on krill, tiny kinds of shrimps only a few centimetres in length. A blue whale must eat enormous amounts of krill every day, so it usually lives in cold waters where there are plentiful supplies.
Blue whale mother and her calfThe blue whale spends its summers in the cold waters around the Arctic ice cap or Antarctica. It feeds on huge quantities of krill. To satisfy its huge appetite, it engulfs about 40 million of them each day. In winter, the blue whale heads for tropical, less food-rich waters, where it mates. Females give birth to a single calf once every two or three years.
A view inside a blue whale's mouth, where a mass of krill has been trapped behind the baleen plates—and will shortly be digested. Like all baleen whales, the blue whale has hundreds of baleen plates, each fringed with stiff hairs hanging from its upper jaw. It uses them as a kind of sieve, trapping the krill from great gulps of seawater.
Close to extinction
A fully grown blue whale's heart, the largest of any animal, is as heavy as a grand piano (around 400 pounds / 180 kilos). Its tongue weighs as much as a female African elephant.
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