The blue whale is not only the biggest animal in the world, it’s the biggest animal to have ever lived on this planet — and scientists have just cracked a big mystery about it.

The blue whale is truly massive: so big, in fact, that in the size department it even beats out ancient giants like the Argentinosaurus, the largest dinosaur that ever lived at 130 feet long and 100 tons. But there’s been one mystery that’s really bugged scientists for a long time: how does the blue whale maintain its enormous size eating such tiny things like krill exclusively? Scientists have found a rather surprising answer: blue whales have a very efficient way of eating, according to a Christian Science Monitor report.

Blue whales gobble up four tons of krill, which are tiny little shrimp-like creatures. They open up their giant mouths and suck up both the krill and many gallons of sea water, then they blast that sea water out using the baleen on their mouths, which filters it out and leaves nothing but that delicious krill behind for them to gulp down.

But a new study that was published in Science Magazine indicates that things are little more complicated than that, according to the Monitor report. After all, Elliott Haze, who is a National Oceanic and Atmospheric Administration (NOAA) ecologist said in a press release that even though scientists have always know that’s how whales eat, they always wondered if that was the whole story. Now, it turns out, it’s not: the whales are optimized their feeding behavior so that there isn’t any wasted effort.

Previous studies indicated that blue whales just open their mouths and suck in the krill when they get a bit peckish. But this new study suggests that it’s a bit more sophisticated than that.

There’s one technique that’s called “bubble netting,” which is when whales dive below a swarm of krill and sound bubbles up to displace them, making the krill easier to snag. But that’s not the only clever way these giant, lumbering beasts use to outsmart their prey. The scientists used digital acoustic recording tags in 55 blue whales off the coast of California to find another clever method to fill their bellies.

For one thing, krill patches can differ in density, so it’s not efficient for the whales to simply go for whatever krill they can spot. If they waste energy on a krill patch with a low density level, it’s not a net positive for the blue whale. So instead, blue whales simply lunge fewer times in each dive if they notice the krill isn’t that dense, which saves oxygen and therefore energy.

So it appears that blue whales can recognize the density of a krill patch and adjust their tactics accordingly: go all out if it’s a dense pack that will allow them to get big mouthfuls, and conserve energy if it’s going to be a smaller mouthful.

The next step for researchers is to figure out if this has something to do with migration patterns. Not all blue whales migrate; some stay in waters swarming with krill near Southern California, but others head out depending on what season it is.

Scientists aren’t sure how many blue whales there are in the world, but they are classified as endangered with between 10,000 and 25,000 blue whales in existence — about 5 percent of the total that were around before the whaling industry started thinning their ranks. The populations are only just now starting to recover due to whaling bans.

The blue whale typically grows to about 98 feet in length and weighs about 200 short tons, making it the largest extant animal and the heaviest in world history.

It is actually a long and slender beast, and it is usually bluish-grey in color, with a lighter underside. It has three subspecies that are distinct, with one occupying the North Atlantic and North Pacific, another in the Southern Ocean, and a third — called the pygmy blue whale — in the Indian and South Pacific oceans. There is some debate over whether there is another subspecies that resides in the Indian Ocean.

At the beginning of the 20th century, the blue whales flourished thanks to the fact that because of its tremendous size, it has virtually no predators. However, the arrival of whalers caused them to be hunted almost to extinction before the international community got involved to protect them in the 1960s. Since then, their numbers have been recovering slowly, but they are still considered endangered. At one point, the Antarctic hosted the largest population of blue whales with a whopping 239,000 individuals. Today, groups number just a couple thousand each. However, there is good news, with the blue whale population off the coast of California almost back to pre-hunting levels.

The mating season for a blue whale begins in the late autumn and tends to continue through the winter. Scientists don’t know much about their mating behavior or where they go to breed.

The life cycle for a female typically involves a birth once ever couple years or so at the start of winter. It has a gestation period of 10 to 12 months, with the calf usually weighing about 3 tons and coming in at a bout 23 feet in length. They are quite thirsty, drinking up to 150 gallons of their mother’s milk every day. After six months, the calf is considered weaned, and has at that point doubled in length. By five to 10 years of age, the whale is sexually mature and can begin mating.

Blue whales live quite a long time, with scientists estimating that they live for at least 80 years. It’s tough to say for sure, however, because records don’t go back to the whaling era, so there may be more time that needs to pass before scientists can say for certain what their age can be. The longest scientists have ever studied an individual whale was 34 years.

The blue whale actually does have a natural predator: the orca. Killer whales are known to sometimes attack blue whales, with about 25 percent of all mature blue whales bearing scars from killer whale attacks. Scientists aren’t sure how often it results in a death.