Giant Squid Eyes Are Basketball-Sized

In the deep ocean's inky blackness, survival often depends on detecting the slightest hint of danger. For the giant squid, its primary predator is the sperm whale. While a whale can use echolocation to find a squid, the squid has evolved a remarkable visual defense. As a massive whale swims, it disturbs microscopic, bioluminescent plankton, causing them to light up and create a faint, glowing trail in the water (Review). The squid's enormous eyes, the largest in the animal kingdom, are perfectly adapted to collect these few photons of light, acting as an early-warning system that can detect a predator from over 300 feet away.

This incredible size is a result of a deep-sea evolutionary arms race. Measuring up to 10 inches in diameter, the eyes are as large as a basketball or a dinner plate—proportionally much larger than the eyes of even the biggest blue whales. This investment in massive optics gives the squid a crucial head start to escape an approaching whale. For centuries, the giant squid was a creature of myth, known only from sailors' tales of the Kraken (Review) and the occasional carcass washed ashore. Modern science revealed that its legendary eyes are not for seeing in the dark, but for seeing the light created by movement within it.