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Blue whales are the largest animals

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that have ever roamed the planet.

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They're at least two times as big as the biggest dinosaurs,

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"That's big!"

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the length of a basketball court,

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and as heavy as 40 African elephants.

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If that's not enough to make you marvel,

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here's something that will.

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They're grown to this enormous size

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by feeding exclusively on tiny shrimp-like creatures called krill

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that are no bigger than your little finger.

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In many ways, the sheer size of krill

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seems to have driven the evolution of the blue whale.

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See, krill are so small

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but are found in dense patches.

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For increased efficiency,

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blue whales have evolved

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to use a feeding strategy

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called lunge feeding.

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Basically, the whale accelerates towards a prey patch

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and opens its mouth wide.

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To increase the capacity, its mouth expands.

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The special, accordion-like blubber layer

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that extends from its snout to its belly button

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enables the whale to engulf large quantities

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of prey-laden water.

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With each giant gulp,

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the whale takes in 125% of its body weight

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in water and krill.

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The whale must then expel the water

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while retaining the yummy krill.

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To do this, it uses its baleen,

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the comb-like structure made of the same stuff

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our nails and hair are made of,

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and its tongue.

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It's pretty crazy that the blue whale's heart

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is as big as a small car,

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a child could crawl through its arteries,

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its tongue weighs as much as an elephant,

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but its esophagus is so small,

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the whale could choke on a loaf of bread.

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These whales are really not designed

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to feed on anything larger than krill.

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It's estimated that blue whales eat four tons of krill per day.

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Because of the incredible design,

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each dive provides the blue whale

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with 90 times as much energy as is used.

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Every mouthful of krill provides almost 480,000 calories,

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the same amount you get from eating 1,900 hamburgers.

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But, why are blue whales so big?

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Blue whales are considerably larger

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than the largest living land animal, the elephant.

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The heavier an animal is,

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the greater its relative surface area.

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As weight increases,

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there's a point at which the legs of that animal

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would simply collapse.

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That explains why elephants don't stand

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on the delicate legs of a horse.

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They need legs shaped like stout pedestals

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to hold their bodies up against gravity.

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In water, the situation is quite different.

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Buoyancy counteracts the gravitational pull on the body

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and their great bulk is therefore partially supported

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by the water.

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So, the ocean is a great place for species

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that want to grow bigger.

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The other secret to their size is their diet.

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By evolving such a huge mouth,

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the whale's have specialized to catch enormous quantities

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of highly abundant and nutritious prey,

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which provides the energy needed to grow so big.

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But, now maybe you're wondering

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why blue whales aren't any bigger?

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After all, the ocean sounds like nirvana

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for any growing beast.

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Well, while lunge feeding may have allowed blue whales

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to become the biggest animal

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to have ever roamed the planet,

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by enabling them to feed efficiently in dense prey patches,

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it isn't cost free.

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Scientists compared all the costs involved with lunge feeding

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to the energy gained from the krill they eat.

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What they found is that when the whale's body increases in size,

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the energy that body demands rises faster

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than the extra energy they get from their food.

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Feeding whales needs 15 times the energy required to remain still

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and 5 times more energy than used when swimming.

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Calculations show

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that the largest a lunge feeder can grow is 33 meters,

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pretty much blue whale size.

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Turns out blue whales have a lot to thank krill for:

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neat, evolutionary adaptations

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that would not have been possible if krill were not so small.

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It's incredible that these tiny creatures

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have allowed blue whales to really push the limits

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of size on our planet.

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Makes you wonder if that old adage,

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"You are what you eat,"

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really does apply in blue whale world.