[4] Humboldt squid typically reach a mantle length of 1.5 m (4 ft 11 in), making the species the largest member of its family.

[5][6] Like other members of the subfamily Ommastrephinae, they possess chromatophores which enable them to quickly change body coloration, known as 'metachrosis’ which is the rapid flash of their skin from red to white.

In Chile, Claude Gay, another French naturalist, obtained some specimens and sent them to the Muséum national d'Histoire naturelle in Paris, where it was determined that the species did not belong with Loligo either.

[15] They notably rapidly flash red and white when captured, earning them the nickname diablo rojo (meaning 'red devil') among local fishermen in Baja California, Mexico.

[22] Electronic tagging has shown Humboldt squid undergo diel vertical migrations, which bring them closer to the surface from dusk to dawn.

[24][25] The Humboldt squid lives at depths of 200 to 700 m (660 to 2,300 ft) in the eastern Pacific (Notably in Chile and Peru), ranging from Tierra del Fuego north to California.

[28] Humboldt squid are generally found in the warm Pacific waters off the Mexican coast; studies published in the early 2000s indicated an increase in northern migration.

Similar trends have been shown off the coasts of Washington, Oregon, and even Alaska, although no year-round Humboldt squid populations are in these locations.

[31] The squid uses its barbed tentacle suckers to grab its prey and slices and tears the victim's flesh with its beak and radula.

Upon reaching striking distance, they open their eight swimming and grasping arms, and extend two long tentacles covered in sharp hooks, grabbing their prey and pulling it back toward a parrot-like beak, which can easily cause serious lacerations to human flesh.

These two longer tentacles can reach full length, grab prey, and retract so fast that almost the entire event happens in one frame of a normal-speed video camera.

Each of the squid's suckers is ringed with sharp teeth, and the beak can tear flesh, although they are believed to lack the jaw strength to crack heavy bone.

[21][33] An investigation of the stomach contents of over 2,000 squid caught outside of the Exclusive Economic Zone off the coasts of Chile found that cannibalism was likely the most important source of food.

[13][41] Jigging involves constantly jerking the line up and down to simulate prey; a reel with an elliptical or oval-shaped hub helps with this.

[14] Compared to other types of seafood, Humboldt squid is inexpensive in Pacific South America, retailing around US$0.30/kg in Peru, and about US$2.00/kg in Chile, in the early 2010s.

[14] In Peru, the practice of making ceviche from cheap squid began in the poorer parts of Lima when the meat became available in the 1990s, and has since spread to Cuzco.

[32] Some scientists claim the only reports of aggression toward humans have occurred when reflective diving gear or flashing lights have been present as a provocation.

Roger Uzun, a veteran scuba diver and amateur underwater videographer who swam with a swarm of the animals for about 20 minutes, said they seemed to be more curious than aggressive.

A 2008 study predicted that ocean acidification will lower the Humboldt squid's metabolic rate by 31% and activity levels by 45% by the end of the 21st century.

It also predicted that the squid wouldn't be able to spend as much of the day in deeper and colder waters, as a larger proportion of the ocean would fall into the oxygen minimum zone.

The episode was about blue whales, but the presenters interviewed fishermen who talked about the exploding diablo rojo population in the Sea of Cortez and human attacks, and showed a squid trying to take a bite of a protectively clad forearm.

[56] In the British Fishing Impossible, mail-clad divers plan to capture a Humboldt squid by hand in the Pacific Ocean, but are prevented from doing so due to bad weather.

[57] In BBC Earth's Blue Planet II the squid's cannibalistic pack hunting was captured on film for the first time.