PUBLISHED September 10, 2010

WATCH: Blue Whales 101 Blue whales are the largest animals to have ever existed. Learn why they're larger than any land animal and why they were hunted for years.

close A blue whale's tongue alone can weigh as much as an elephant—its heart as much as an automobile. Photograph by Hiroya Minakuchi, Minden Pictures/Nat Geo Image Collection close Earth's largest animal, the blue whale can eat some 4 to 8 tons of krill per day. Photograph by Flip Nicklin, Nat Geo Image Collection close Tap images for captions

Common Name: Blue Whale Scientific Name: Balaenoptera musculus Type: Mammals Diet: Carnivore Average life span in Captivity: 80 to 90 years. Size: 82 to 105 feet Weight: Up to 200 tons Size relative to a bus IUCN Red List Status: close The IUCN Red List of Threatened Species is widely recognized as the most comprehensive, objective global approach for evaluating the conservation status of plant and animal species. lc Least Concern At relatively low risk of extinction nt Near Threatened Likely to become vulnerable in the near future vu Vulnerable At high risk of extinction in the wild en Endangered At very high risk of extinction in the wild cr Critically Endangered At extremely high risk of extinction in the wild ew Extinct in the Wild Survives only in captivity ex Extinct No surviving individuals in the wild or in captivity Data Deficient Not enough information available to make an assessment Not Evaluated No assessment has been made ? Endangered lc nt vu en cr ew ex least concern extinct Current Population Trend: Increasing arrow-up

What is the blue whale?

Blue whales are the largest animals ever known to have lived on Earth. These magnificent marine mammals rule the oceans at up to 100 feet long and upwards of 200 tons. Their tongues alone can weigh as much as an elephant. Their hearts, as much as an automobile.

Diet of krill

Blue whales reach these mind-boggling dimensions on a diet composed nearly exclusively of tiny shrimplike animals called krill. During certain times of the year, a single adult blue whale consumes about 4 tons of krill a day.

Blue whales are baleen whales, which means they have fringed plates of fingernail-like material, called baleen, attached to their upper jaws. The giant animals feed by first gulping an enormous mouthful of water, expanding the pleated skin on their throat and belly to take it in. Then the whale's massive tongue forces the water out through the thin, overlapping baleen plates. Thousands of krill are left behind—and then swallowed.

Coloring and appearance

Blue whales look true blue underwater, but on the surface their coloring is more a mottled blue-gray. Their underbellies take on a yellowish hue from the millions of microorganisms that take up residence in their skin. The blue whale has a broad, flat head and a long, tapered body that ends in wide, triangular flukes.

Vocalization and behavior

Blue whales live in all the world's oceans, except the Arctic, occasionally swimming in small groups but usually alone or in pairs. They often spend summers feeding in polar waters and undertake lengthy migrations towards the Equator as winter arrives.

These graceful swimmers cruise the ocean at more than five miles an hour, but accelerate to more than 20 miles an hour when they are agitated. Blue whales are among the loudest animals on the planet. They emit a series of pulses, groans, and moans, and it’s thought that, in good conditions, blue whales can hear each other up to 1,000 miles away. Scientists think they use these vocalizations not only to communicate, but, along with their excellent hearing, to sonar-navigate the lightless ocean depths.

Blue whale calves

Calves enter the world already ranking among the planet's largest creatures. After about a year inside its mother's womb, a baby blue whale emerges weighing up to 3 tons and stretching to 25 feet. It gorges on nothing but mother's milk and gains about 200 pounds every day for its first year.

Longevity

Blue whales are among Earth's longest-lived animals. Scientists have discovered that by counting the layers of a deceased whale's waxlike earplugs, they can get a close estimate of the animal's age. The oldest blue whale found using this method was determined to be around 110 years old. Average lifespan is estimated at around 80 to 90 years.

Conservation

Aggressive hunting in the 1900s by whalers seeking whale oil drove them to the brink of extinction. Between 1900 and the mid-1960s, some 360,000 blue whales were slaughtered. They finally came under protection with the 1966 International Whaling Commission, but they've managed only a minor recovery since then.

Blue whales have few predators but are known to fall victim to attacks by sharks and killer whales, and many are injured or die each year from impacts with large ships.