This 1,000-Pound Colossus Has The Largest Eyes In The Animal Kingdom

We know more about our solar system—celestial bodies and the vacuous expanses between them—than we do about the oceans on our planet. Despite centuries of study, we’ve barely scratched the surface, with close to 95% of these watery depths yet unexplored by humans. Their secrets continue to unfurl.

Case in point: The colossal squid, Mesonychoteuthis hamiltoni, is so rare that as of August 2024, we still haven’t managed to capture clear footage of an adult alive in its natural habitat, despite remarkable advancements in camera technology and dedicated efforts like the KOLOSSAL project.

For the longest time, its more famous cousin the giant squid, Architeuthis dux, was believed to be the largest of its kind. That is, until 1925, when the first specimen of colossal squid was described based on two tentacles found inside a whale’s stomach. In fact, a lot of the information we know about it has only been gleaned through parts discovered in the stomach of its primary predator, the sperm whale.

The Colossal Squid Is A Product Of ‘Abyssal Gigantism’

You may have heard of the phenomenon of island gigantism, where isolated species grow to immense sizes. Abyssal gigantism is a similar concept, but it occurs in the deep sea.

The deep sea essentially functions like an island, according to a September 2006 article published in the Journal of Biogeography. In both environments, food is scarce, leading to unique evolutionary pressures.

In the abyss, small-bodied species can evolve to become significantly larger, as larger body sizes can be advantageous in the following ways:

• Larger bodies can increase the potential for energy storage. This is crucial in a habitat where food is hard to come by.
• Additionally, larger size might help these species survive longer in the cold, dark depths of the ocean, where biological processes are slower.

The colossal squid, with its massive body, is a prime example of how abyssal gigantism allows deep-sea creatures to thrive in extreme conditions​.

These giants have a lifespan of around 40 years, and they are built like an underwater tank, too. They can grow up to 46 feet in length and weigh as much as 1,091 pounds, earning themselves the status of the largest invertebrate on the planet. Unlike most squids, which have slender, streamlined bodies, these stocky titans of the ocean possess a robust, muscular mantle—an outer covering that provides a sturdy body structure. This might help them withstand the immense pressures of their deep-water environment.

The Largest Eyes On The Planet—Documented Diameter Up To 11 Inches

Though the colossal squid’s eye size is sometimes exaggerated in popular media, it does possess the largest documented eyes of any known animal on the planet.

“Giant and colossal squid share the pelagic depths with a number of large vertebrates whose eyes are just a fraction of the size of those of the squid. This strongly indicates that giant and colossal squid use their eyes for a purpose not shared by other animals,” the authors of an April 2012 report published in Current Biology explain.

The largest colossal squid ever captured (as of 2012), an adult specimen from New Zealand, had eyes with a diameter of 11 inches. This colossal creature holds the record for the largest eyes in the natural world, with diameters close to the theoretical maximum for both colossal and giant squids.

For context, the fish with the largest eyes is the swordfish (Xiphias gladius), which can have eyes up to 9 cm (3.5 inches) in diameter. This is almost three times smaller than the colossal squid’s eyes. The large eyes of the swordfish help it hunt in the deep ocean’s dimly lit environments.

So What Is The ‘Other Purpose’ Of The Colossal Squid’s Giant Eyes?

The colossal squid’s giant eyes are primarily adapted for detecting large predators, particularly sperm whales, in the deep sea. And unlike other sea creatures that might use their eyes to spot food or mates, the colossal squid’s massive eyes are specifically tuned to detect bioluminescence—the faint light produced by tiny organisms disturbed by a large moving predator.

In the deep, dark waters where the colossal squid lives, this bioluminescence can act as a warning signal, allowing the squid to detect an approaching sperm whale from a significant distance (up to 120 meters).

This ability is crucial for the colossal squid’s survival—detecting bioluminescence from afar gives these behemoths the necessary time to prepare an evasive response to the predator. So the purpose of the colossal squid’s giant eyes is not just for general vision, but specifically for predator detection in the deep ocean, where survival often depends on the ability to see and react to these subtle visual cues.

As we approach the 100th anniversary of its discovery, efforts like the KOLOSSAL project and other research initiatives are intensifying to unravel the many mysteries surrounding the colossal squid. These efforts aim to learn more about its biology, behavior and the role it plays in the deep-sea ecosystem.

Does the existence of this colossal creature make you feel small? Or does it ignite a deeper connection to the mysteries of the natural world? Take this test to explore how your perspective aligns with the wonders of our planet: Connectedness To Nature Scale