Image credit: Fir0002/Flagstaffotos, Wikimedia Commons // CC BY-NC

Since ancient times, philosophers and naturalists have puzzled over this deep-sea enigma. There’s plenty we still don’t know about giant squid, but we’ve learned quite a lot—especially over the past 20 years. 

1. Giant Squid Have Eyes the Size of Frisbees.

Image credit: Smithsonian Institution, Wikimedia Commons // Public Domain

A staggering 10.5 inches across, a squid’s eyeballs lack the jelly-like substance that gives ours shape. Instead, they’re filled with water, which leaks out once the invertebrate dies. Its eyes “collapse… [like a] plastic bag”, according to biologist Dan-Eric Nilsson.

2. Females are Bigger than Males.

On average, females are around twice the size of (and around 10 feet longer than) their potential mates.   

3. Their Suckers Can Leave Ugly Battle Scars.  

Giant squid have to be wary around sperm whales; the marine mammals gobble them up en masse. While under attack, the squid often retaliate by inflicting large, circular wounds, courtesy of the serrated rings around each sucker.

4. Forty-Three Feet or So Seems to Be the Giant Squid’s Maximum Length.

At least, that’s what the available evidence tells us. Reports of 60- and 70-footers have never been verified scientifically.

5. Instead of a Proper Tongue, They Use a “Radula.”

This organ rests inside their beaks and is covered with seven rows of denticles—sharp, toothy, backwards-pointing protrusions. 

6. There’s Just One Known Species.

Until recently, many thought that there might be several varieties out there, but a genetic analysis performed in 2013 said otherwise: Architeuthis dux, researchers found, is the only species of this genus, as revealed by a comparison of 43 specimens from various seas and oceans. The giant squid gene pool seems abnormally shallow—all 43 subjects were pretty much indistinguishable in this regard. “It’s completely bizarre,” geneticist Thomas Gilbert said. “How can something be global but have so little variation?”

7. Their Tentacles Can Regenerate.

One giant squid corpse found in Canada in 1968 had a partially regenerated tentacle. According to a study of the specimen, "The regenerated club differed in length and width, and in the size and pattern of suckers, when compared with the normal tentacular arm." Many cephalopods besides squid are capable of this feat, including octopuses (and, yes, “octopuses” is a perfectly-acceptable plural, as are “octopi” and “octopodes”).

8. An Estimated 4.3 to 131 Million Get Eaten by Sperm Whales Each Year.

The squid regularly show up inside sperm whale stomachs and, not too long ago, a female was even seen carrying one around in her jaws. Approximately 360,000 of these mammals patrol our oceans. So, if every sperm whale on earth devoured an average of one giant squid per month, that means 4.3 million would be offed annually.

But some experts think this figure is way too low. Every single day, male whales put away 300 to 400 squid of various species, while females consume an outrageous 700 to 800 squid. Should Architeuthis represent even 1 percent of their diet, then the beasts eat 3.6 million daily. That’s 131 million squid killed annually.

9. This Cephalopod May Have Helped Give Rise to Sea Serpent Legends.

In one of Moby Dick’s more memorable chapters, an Architeuthis slithers towards Captain Ahab’s ship. Apparently, Herman Melville wasn’t a fan—he described the squid as a “vast, pulpy mass” complete with “innumerable long arms radiating from its centre, curling and twisting like a nest of anacondas.” Unflattering, right? But Melville wasn't alone. Many believe that this predator’s writhing, snake-like limbs have long inspired sea serpent yarns.

10. Twenty Thousand Leagues Under the Sea Grossly Overestimates the Giant Squid’s Usual Weight.

Jules Verne’s 1869 masterpiece remains impressive beyond all measure. After all, his novel predicted the invention of both scuba tanks and taser guns. But there are still a few gaffes to be found, particularly during the book’s most iconic scene. When hordes of giant squid attack, the narrator—a French professor named Pierre Arronax—estimates that each one must weigh “between four and five thousand pounds.” But as far as modern scientists can tell, the heaviest animals weigh around a ton—although most are less than 1000 pounds

11. Like All Squids, They’ve Got Three Hearts.

A median heart pumps oxygenated blood throughout the body, which it receives from two smaller ones that pump blood through the gills

12. Architeuthis Penises Are About a Yard Long.

Nobody has ever documented a pair of giant squid getting busy. But biologists suspect that males use their sex organs like syringes, injecting sperm into a female’s skin, where she stores the cells until her eggs need fertilizing. When that happens, the mom-to-be pulls them out of storage (though we’re not sure how).

13. The First Giant Squid Photo Ever Shot was Taken Inside of a Bathroom.

Image credit: Wikimedia Commons

In 1873, Newfoundland preacher Moses Harvey acquired a dead Architeuthis which he laid out over his shower curtain and preserved for posterity. He’d purchased this specimen for just $10 from a few local fishermen who’d ensnared it with their nets while out in Logy Bay.

14. Giant Squid Might Be Cannibals.

Bits and pieces of one Architeuthis showed up in one cadaver's stomach. But this doesn’t necessarily prove that giant squid dine on one another—some scientists speculate that the individual in question may have accidentally swallowed a few parts of itself somehow.

15. The Smithsonian Has Two On Display.

You can see them in the National Museum of Natural History’s Sant Ocean Hall. The pair represents both sexes—here’s a quick look at their 25-foot female (it was probably 36 feet while alive):

16. Their Brains are Donut-Shaped.

But that’s not the weird part. What’s truly bizarre (at least from our mammal-centric perspective) is the fact that its esophagus passes through the hole in the middle of its brain. Giant squids have to be really careful while swallowing, because if a given meal isn’t broken down into small enough pieces first, it can rub against the brain and cause damage.

17. Before 2004, Nobody Had Ever Snapped any Pictures of a Live One …

History was made by residents of the Ogasawara Islands (located 600 miles south of Japan) on September 30, 2004. Using a line baited with shrimp, zoologist Tsunemi Kubodera and whale-watcher Kyochi Mori attracted an Architeuthis about 2950 feet beneath their vessel. Five hundred still images were then snapped by a submerged camera before the squid took off—leaving behind an 18-foot severed tentacle.

18. … And The World’s First Giant Squid Video Didn’t Arrive Until 2006.

Kubodera would top himself that year when his crew videotaped a young female as they dragged her up to the surface. “We believe this is the first time anyone has successfully filmed a giant squid that was alive,” he said. “Now that we know where to find them, we think we can be more successful at studying them in the future.” Sadly, Kubodera’s prize died during the ordeal.

19. Jellyfish Help Architeuthis Hunt.

They say the enemy of your enemy is your friend. Certain jellyfish possess a dazzling talent called bioluminescence, which means that they can light themselves up and illuminate the ocean’s inky depths. Predators like giant squid eat many of the fish that hunt jellyfish. So, if a bioluminescent jelly finds itself under attack, it can issue a cry for help by flashing a distress signal, in the hopes that it might attract an even larger carnivore and scare off its assailant.

In 2012, an oceanographic team would capitalize on this display. After rigging a deep-sea camera with a lure built to resemble a brightly-lit jellyfish, Dr. Edie Widder and her colleagues filmed some majestic Architeuthis footage, as she explains in her terrific TED talk:

20. It’s Not the Only Monster-Sized Squid Out There.

Meet Mesonychoteuthis hamiltoni, better known as the colossal squid. Though Architeuthis probably exceeds it length-wise, this animal is heavier on average, has even bigger eyeballs, and wields swiveling hooks on its tentacles. Needless to say, this isn't a creature you’d want to mess with.