Invertebrates
Colossal Squid
Mesonychoteuthis hamiltoni · also called colossal squid, Antarctic squid
The colossal squid is the largest invertebrate on the planet by weight — a half-tonne Antarctic predator with dinner-plate eyes and rotating hooks on its arms. It is also almost entirely a mystery: nearly everything known about it has been reconstructed from the parts left in sperm-whale stomachs.
Overview
The colossal squid lives in the deep Southern Ocean around Antarctica, mostly 1,000–2,000 metres down, ranging north toward the southern tips of the continents. It is thought to be a slow, ambush predator — hanging in the water, conserving energy in the cold, and seizing large fish such as Antarctic toothfish and other squid that come within reach. One estimate suggests an adult needs only about 30 grams of food a day.
The largest invertebrate
The giant squid is longer, thanks to its stretched feeding tentacles, but the colossal squid is far bulkier — a large one is estimated at around 10 metres and up to 500 kilograms, making it the heaviest invertebrate known.
Eyes and hooks
Its eyes are about 27 centimetres across — the largest of any animal, with a built-in light organ. They appear to be tuned to spotting the faint glow of an approaching sperm whale from over 100 metres in the dark. Its arms and the club ends of its two long tentacles carry swivelling, three-pointed hooks — unusual among big squid — that leave scars on whale skin.
Known from the dead
For most of its history the colossal squid was known only from beaks and fragments in sperm-whale stomachs and the occasional whole animal on a toothfish longline. A near-complete ~495 kg specimen is on display at Te Papa in New Zealand. In 2025 a young colossal squid was filmed alive in the deep sea for the first time; a large adult has still never been seen in its habitat.
Status
The colossal squid is listed as Least Concern. Its true abundance is unknown, but it is considered common in the Southern Ocean, judging by how regularly its remains appear in the animals that eat it.
Colossal Squid: common questions
What is the difference between the colossal squid and the giant squid?
They are different animals in different families. The giant squid (Architeuthis) is longer — its two feeding tentacles can stretch its total length to 12 or 13 metres — but it is relatively slender and lighter, maybe up to 275 kilograms. The colossal squid (Mesonychoteuthis) has a shorter, much bulkier body and heavier arms, and estimates put a large one at around 10 metres and up to 500 kilograms, so it is the heavier of the two and the largest invertebrate by mass. The colossal squid also lives only in the Southern Ocean, has swivelling hooks rather than just suckers with toothed rings, and has even larger eyes.
Why does it have such enormous eyes?
Its eyes are roughly 27 centimetres across, larger than any other animal's known, living or extinct. Research suggests this is specifically an adaptation for detecting sperm whales. In the deep, dark Southern Ocean, a hunting sperm whale disturbs bioluminescent plankton and creates a faint glow around itself as it moves. An eye that big can pick up that dim, large-scale glow from over 100 metres away — far enough for the squid to react and try to evade — whereas a smaller eye would only see the whale once it was too close. Beyond a certain size, bigger eyes stop helping with small nearby targets and only help with large distant ones, and avoiding whales fits that exactly.
Has a living colossal squid ever been seen?
Only rarely and briefly. For most of its history the species was known almost entirely from beaks and body parts recovered from the stomachs of sperm whales and from Antarctic toothfish longlines, which occasionally haul up a whole animal. A few nearly intact specimens have been landed by fishing vessels, one of which (about 495 kg) is displayed at the Museum of New Zealand Te Papa. In 2025, an expedition filmed a young colossal squid alive in the deep sea for the first time. A large adult has still never been observed alive in its habitat.
Is the colossal squid dangerous to humans?
In practical terms, no — it lives at depths and in a region where people essentially never go, and there is no record of one harming a person. It is undoubtedly capable of inflicting serious wounds with its beak and rotating hooks, as the scars on sperm whales attest, and a large individual is far bigger and stronger than a human. But encounters are limited to dead or dying animals brought up by deep fishing gear. The "giant squid attacking ships" of legend refers to no real documented event with either giant or colossal squid.