The big facts page

118 octopus facts, all checked

Every fact on this site, in one place, each linked to its source. Figures that can change carry the date we checked them (28 Oct 2026). Where sources disagree we give every figure: see when sources disagree.

Octopuses in general

1 There are roughly 300 species of octopus, and the number keeps changing as new species are discovered. Smithsonian Ocean: Octopuses, squids and relatives · checked 28 Oct 2026
2 Octopuses are molluscs: boneless invertebrates related to clams. Monterey Bay Aquarium: Giant Pacific octopus
3 Cephalopod, the group octopuses belong to, means ‘head foot’ in Greek, because the head connects straight to the arms. Smithsonian Ocean: Octopuses, squids and relatives
4 Octopuses have eight arms. Squid and cuttlefish have eight arms plus two longer tentacles for snatching prey. Smithsonian Ocean: Octopuses, squids and relatives
5 Most octopuses spend most of their time on the ocean floor, and most live alone in a den. Smithsonian Ocean: Octopuses, squids and relatives
6 Octopuses usually live no more than a year. The giant Pacific octopus is a long-lived exception, at about three to five years. Monterey Bay Aquarium: Giant Pacific octopus
7 Only the chambered nautiluses still have a shell on the outside. Over 10,000 nautiloid species once lived; today just seven remain. Smithsonian Ocean: Octopuses, squids and relatives
8 The largest cephalopod, the giant squid, is longer than a school bus. Like other squid it has eight arms plus two long feeding tentacles. Smithsonian Ocean: Octopuses, squids and relatives
9 Despite its name, the vampire squid is more closely related to octopuses than to squid. It’s harmless, eating drifting particles. Smithsonian Ocean: Octopuses, squids and relatives
10 Genetic studies show cuttlefish belong among the squids, not in a separate line of their own. Smithsonian Ocean: Octopuses, squids and relatives
11 The Humboldt squid is a fearsome predator that grabs prey with toothed sucker rings. Smithsonian Ocean: Octopuses, squids and relatives

Bodies and senses

12 Octopuses have three hearts. Two branchial hearts push used blood through the gills, and a systemic heart pumps the fresh, oxygen-rich blood around the body. Smithsonian Ocean: Octopuses, squids and relatives
13 The heart that pumps blood round the body stops beating while an octopus swims, which is why octopuses prefer crawling: swimming exhausts them. Shedd Aquarium: Eight strange and wonderful facts about octopuses
14 Their blood really is blue. It carries oxygen with a copper-based molecule called hemocyanin, while our blood uses iron. Smithsonian Ocean: Octopuses, squids and relatives
15 Copper-based hemocyanin carries oxygen better than our iron-based hemoglobin when the water is cold and low in oxygen. Shedd Aquarium: Eight strange and wonderful facts about octopuses
16 When an octopus’s blood loses its oxygen (when the animal dies, for example) it stops being blue and turns clear. Natural History Museum, London: Octopuses keep surprising us
17 Like us, octopuses have a closed circulatory system: their blood travels round the body inside vessels. National Aquarium: Otherworldly octopuses
18 Each of an octopus’s eight arms has its own ‘mini brain’, and each arm can taste, touch and move without direction from the centre. Natural History Museum, London: Octopuses keep surprising us
19 Counting the central brain and the eight arm ‘mini brains’, the Natural History Museum describes octopuses as having nine brains. Natural History Museum, London: Octopuses keep surprising us
20 The common octopus has around 500 million neurons, about as many as a dog. About two thirds of them are in its arms. Natural History Museum, London: Octopuses keep surprising us
21 The rest of the neurons are in a doughnut-shaped brain wrapped around the octopus’s oesophagus (food pipe). Natural History Museum, London: Octopuses keep surprising us
22 An octopus’s brain-to-body ratio is the largest of any invertebrate, and bigger than many vertebrates’ (though not mammals’). Natural History Museum, London: Octopuses keep surprising us
23 In a 2011 experiment, octopuses learned to steer a single arm through a maze to food, using their eyes: proof the central brain can take charge of an arm. Natural History Museum, London: Octopuses keep surprising us
24 An octopus’s arms carry more than 2,000 suckers, each able to move on its own. Shedd Aquarium: Eight strange and wonderful facts about octopuses
25 The suckers have chemical sensors, so they don’t just feel: they taste and smell too. Shedd Aquarium: Eight strange and wonderful facts about octopuses
26 Harvard scientists found a family of ‘chemotactile receptors’ in the suckers that let octopuses taste by touch. The receptors are found only in cephalopods (Cell, 2020). Harvard Molecular & Cellular Biology: How the octopus ‘tastes’ by touch
27 Each arm’s suckers work as the octopus version of both a tongue and hands. Harvard Molecular & Cellular Biology: How the octopus ‘tastes’ by touch
28 With no bones, an octopus can squeeze through any gap big enough for its beak, which is made of chitin. National Aquarium: Otherworldly octopuses
29 Octopuses eat with a sharp beak. Inside it, a tongue-like radula lined with tiny teeth can push food down or drill holes in shells. Smithsonian Ocean: Octopuses, squids and relatives
30 Octopuses can jet away by squirting water from the mantle through the funnel, but bottom-dwelling octopuses usually save jet propulsion for escapes and walk on their arms instead. Smithsonian Ocean: Octopuses, squids and relatives
31 A 2005 study found that the coconut octopus and the algae octopus can tiptoe backwards on just two arms. Smithsonian Ocean: Octopuses, squids and relatives
32 Colour changes come from thousands of pigment-filled cells called chromatophores. Muscles stretch each one open to show its red, brown or yellow pigment. Smithsonian Ocean: Octopuses, squids and relatives
33 Octopuses change texture as well as colour, by raising bumps on their skin called papillae. Smithsonian Ocean: Octopuses, squids and relatives
34 Cephalopods have only one type of light-receptor cell, so they are most likely colour-blind. But a recent study suggests their oddly shaped pupils might let some of them tell colours apart anyway. Nobody knows for sure yet. Smithsonian Ocean: Octopuses, squids and relatives
35 Almost all cephalopods have an ink sac that can release a sudden plume of dark ink, made from melanin and a thick mucus. Smithsonian Ocean: Octopuses, squids and relatives
36 Octopus ink isn’t just a smokescreen. It contains tyrosinase, which irritates a predator’s eyes and scrambles its senses of smell and taste. Smithsonian Magazine: Ten wild facts about octopuses
37 All octopuses are venomous, but only the blue-ringed octopuses are dangerous to people. Shedd Aquarium: Eight strange and wonderful facts about octopuses
38 A few shore-dwelling octopuses make short trips out of the water at low tide, but they can only last a few minutes before crawling back to the sea. Shedd Aquarium: Eight strange and wonderful facts about octopuses
39 The giant Pacific octopus’s shell has shrunk to two small plates where its head muscles anchor. Monterey Bay Aquarium: Giant Pacific octopus

Smarts and behaviour

40 Octopuses can untie knots, open jars and get into toddler-proof cases, and they are expert escape artists. Smithsonian Ocean: Octopuses, squids and relatives
41 There is growing evidence that octopuses have personalities: one may be shy, another curious and playful, another cranky. Smithsonian Ocean: Octopuses, squids and relatives
42 There is evidence that octopuses can recognise individual people, and have favourites. National Aquarium: Otherworldly octopuses
43 Britannica says the common octopus is thought to be the most intelligent of all invertebrates. Britannica: Octopus
44 In 2016 an octopus called Inky escaped from the National Aquarium of New Zealand in Napier. His tank lid had been left slightly open; he slid across the floor and down a 15 cm drain pipe that led to the sea. BBC News: Octopus makes great escape from New Zealand aquarium
45 Inky was a male common New Zealand octopus, and he made his escape during the night. National Geographic: Inky’s daring escape
46 Veined octopuses in Indonesia collect coconut-shell halves, stack them, carry them across the seafloor on stiffened arms and later hide inside: one of the first reports of tool use by an invertebrate. ScienceDaily, reporting Finn, Tregenza & Norman 2009, Current Biology
47 The mimic octopus can impersonate a banded sole (a poisonous flatfish), a lionfish and a banded sea snake, changing its shape, texture and movement to match. American Museum of Natural History: The talented mimic octopus
48 To play a sea snake, the mimic octopus hides six arms and stretches the other two out in opposite directions. American Museum of Natural History: The talented mimic octopus
49 The mimic octopus was discovered in 1998. It was the first animal known to switch between impersonating several different animals. American Museum of Natural History: The talented mimic octopus · checked 28 Oct 2026
50 The mimic octopus has its own copycat: the harlequin jawfish hides among its arms, matching their stripes. American Museum of Natural History: The talented mimic octopus
51 Most octopuses live alone, but gloomy octopuses gather in underwater ‘cities’ researchers nicknamed Octopolis and Octlantis. Smithsonian Ocean: Octopuses, squids and relatives
52 Octopus arms are so independent that, in one experiment, arms cut from a dead animal still jerked and curled up when pinched. Smithsonian Magazine: Ten wild facts about octopuses

The species

53 The giant Pacific octopus is the largest octopus species. Monterey Bay Aquarium: Giant Pacific octopus
54 A female giant Pacific octopus has about 2,240 suckers; males have about 100 fewer. Monterey Bay Aquarium: Giant Pacific octopus
55 The giant Pacific octopus hatches from an egg the size of a grain of rice. The hatchling weighs 22 milligrams. Monterey Bay Aquarium: Giant Pacific octopus
56 The giant Pacific octopus lives in the North Pacific, from Korea and Japan to Canada, the US and Mexico, in water of 60°F (about 16°C) or colder, from tide pools to 1,500 m deep and more. Monterey Bay Aquarium: Giant Pacific octopus
57 Monterey Bay Aquarium: a full-grown giant Pacific octopus can weigh more than 50 pounds (23 kg). The heaviest on record weighed 200 pounds (91 kg) and measured nearly 20 feet (6 m) across. Monterey Bay Aquarium: Giant Pacific octopus · checked 28 Oct 2026
58 NOAA’s Kodiak lab: giant Pacific octopuses average 30–50 lbs and 6–8 feet long, and the largest recorded, caught in Alaska, weighed over 600 pounds. NOAA Fisheries: Inside the Kodiak Lab aquarium (giant Pacific octopus) · checked 28 Oct 2026
59 Britannica: the giant Pacific octopus may grow to 5.4 metres (18 feet) long, with an arm span of almost 9 metres. Britannica: Octopus · checked 28 Oct 2026
60 NOAA’s Kodiak lab says the giant Pacific octopus has the longest lifespan of any octopus species, 3 to 5 years. NOAA Fisheries: Inside the Kodiak Lab aquarium (giant Pacific octopus) · checked 28 Oct 2026
61 A female giant Pacific octopus lays an average of 50,000 eggs, which helps make the species naturally resilient. Monterey Bay Aquarium: Giant Pacific octopus
62 The Monterey Bay Aquarium says the giant Pacific octopus is not endangered. Monterey Bay Aquarium: Giant Pacific octopus · checked 28 Oct 2026
63 NOAA’s Kodiak lab cared for a giant Pacific octopus called Pi, released back into the wild in January 2021 at nearly 5 feet long. NOAA Fisheries: Inside the Kodiak Lab aquarium (giant Pacific octopus)
64 At least eight species of octopus live in Alaskan waters. NOAA Fisheries: Octopus research in Alaska
65 The common octopus (Octopus vulgaris) is the best-known octopus. It lives in tropical and temperate seas worldwide, hides in holes and crevices on rocky bottoms and feeds mainly on crabs. Britannica: Octopus
66 Britannica reports that the giant Pacific octopus can change colour in a tenth of a second. Britannica: Octopus
67 Britannica: the smallest octopus, Octopus arborescens, is about 5 cm (2 inches) long. Britannica: Octopus · checked 28 Oct 2026
68 Smithsonian Ocean: the smallest cephalopods, like the California lilliput octopus, could sit on the tip of your finger. Smithsonian Ocean: Octopuses, squids and relatives · checked 28 Oct 2026
69 The blue-ringed octopus isn’t one species but a whole genus, Hapalochlaena, all with glowing blue rings. Australian Institute of Marine Science: Blue-ringed octopus
70 Blue-ringed octopuses are small: 4 to 6 cm long, with arms 7 to 10 cm long. Australian Institute of Marine Science: Blue-ringed octopus
71 The blue rings usually only flash when the octopus feels threatened. Australian Institute of Marine Science: Blue-ringed octopus
72 Its venom is tetrodotoxin, made by bacteria that live in its salivary glands. Australian Institute of Marine Science: Blue-ringed octopus
73 Blue-ringed octopuses are shy and usually dart for cover when they meet people. They only bite if picked up, and the bite may not even be felt. Australian Museum: Blue-lined octopus
74 Australian Museum (southern blue-lined octopus page): blue-ringed octopuses have caused at least three human deaths and many near-deaths. Australian Museum: Southern blue-lined octopus · checked 28 Oct 2026
75 Australian Museum: there have been several deaths in Australia from the blue-lined octopus and its relatives. Australian Museum: Blue-lined octopus · checked 28 Oct 2026
76 Fast mouth-to-mouth rescue breathing has saved more than 10 documented bite victims. If you suspect a bite, get medical help immediately. Australian Museum: Southern blue-lined octopus · checked 28 Oct 2026
77 Victims can’t move or answer, but they stay fully conscious. Australian Museum: Southern blue-lined octopus
78 The mimic octopus was discovered off Sulawesi, Indonesia. Most sightings come from Indonesia, though it has been seen as far away as the Great Barrier Reef. National Geographic: Mimic octopus
79 The mimic octopus grows up to 24 inches (about 60 cm) long, arms included. National Geographic: Mimic octopus
80 Dumbo octopuses are deep-sea octopuses with two ear-like fins on the sides of the body, which they use to float and swim. Smithsonian Ocean: Octopuses, squids and relatives
81 The dumbo octopus has no ink sac. In the permanent dark of the deep sea there is little point. NOAA Ocean Exploration: Cephalopods
82 NOAA Ocean Exploration: the dumbo octopus is one of the deepest-living octopuses and has been found 4,000 metres deep. NOAA Ocean Exploration: Cephalopods · checked 28 Oct 2026
83 In 2019, cameras filmed a dumbo octopus (Grimpoteuthis) 6,957 metres down in the Java Trench, Indian Ocean: the deepest cephalopod ever reliably seen. Jamieson & Vecchione 2020, Marine Biology (peer-reviewed) · checked 28 Oct 2026
84 That sighting pushed the known depth limit for cephalopods down by 1,812 metres. Jamieson & Vecchione 2020, Marine Biology (peer-reviewed) · checked 28 Oct 2026
85 In 2016, scientists on NOAA’s Okeanos Explorer discovered a ghostly ‘Casper’ octopus about 4,000 metres down in the central Pacific. Smithsonian Ocean: Octopuses, squids and relatives · checked 28 Oct 2026
86 The paper nautilus, or argonaut, is actually an octopus. The female makes a paper-thin, shell-like egg case. Smithsonian Ocean: Octopuses, squids and relatives
87 The argonaut traps air in its papery case at the surface and dives until the squashed air bubble balances its weight. Smithsonian Ocean: Octopuses, squids and relatives
88 The day octopus (Octopus cyanea) can shape itself like algae or coral to hide from predators or stalk prey. Smithsonian Ocean: Octopuses, squids and relatives

Life cycle

89 For most cephalopods, mating is a once-in-a-lifetime event: both male and female die shortly afterwards. Smithsonian Ocean: Octopuses, squids and relatives
90 The male uses a specially modified arm, the hectocotylus, to pass packets of sperm to the female. Britannica: Octopus
91 The mother stops eating and spends her time fanning the eggs with water to keep them clean and guarding them from predators. Smithsonian Ocean: Octopuses, squids and relatives
92 Octopuses typically breed once and then die. In most shallow-water species the mother tends her eggs for 1 to 3 months. Robison et al. 2014, PLOS ONE (peer-reviewed)
93 Female blue-ringed octopuses care for their eggs until they hatch, and usually die once the job is done. Australian Institute of Marine Science: Blue-ringed octopus
94 A deep-sea octopus, Graneledone boreopacifica, brooded her eggs for 53 months (May 2007 to September 2011) at 1,397 m in Monterey Canyon: the longest egg-brooding period known for any animal. Robison et al. 2014, PLOS ONE (peer-reviewed) · checked 28 Oct 2026
95 Scientists counted the empty egg capsules afterwards and estimate she was guarding between 155 and 165 eggs. Robison et al. 2014, PLOS ONE (peer-reviewed)
96 The previous record for octopus brooding was 14 months, for Bathypolypus arcticus in the lab. Robison et al. 2014, PLOS ONE (peer-reviewed) · checked 28 Oct 2026
97 The very long development time is most likely a response to the cold of the deep sea. Smithsonian Ocean: Octopuses, squids and relatives
98 MBARI researchers dived to the brooding mother 18 times over four and a half years, and found her in the same place every time, recognisable by her scars. MBARI: Deep-sea octopus broods eggs for over four years
99 A giant Pacific octopus lives alone until the very end of its life, when it seeks out a mate, reproduces and dies soon after. Monterey Bay Aquarium: Giant Pacific octopus
100 Giant Pacific octopus hatchlings are just over a quarter of an inch long, with about 14 suckers on each arm, and drift in surface waters eating plankton. Monterey Bay Aquarium: Giant Pacific octopus
101 In all that time the researchers never saw her leave her eggs or eat anything, not even small crabs and shrimp that wandered past. MBARI: Deep-sea octopus broods eggs for over four years

Where they live

102 With luck and sharp eyes, you might spot a giant Pacific octopus in a tide pool. Monterey Bay Aquarium: Giant Pacific octopus
103 There is no fishery aimed at octopus in Alaska, but giant Pacific octopuses are caught by accident in trawl, longline and pot fisheries, and NOAA monitors that catch. NOAA Fisheries: Octopus research in Alaska

Food and predators

104 A telltale sign of an octopus den is a pile of empty crab shells on a rocky bottom. Smithsonian Ocean: Octopuses, squids and relatives
105 Giant Pacific octopuses eat mostly crabs, clams and other molluscs. Monterey Bay Aquarium: Giant Pacific octopus
106 To break into a shell, an octopus pulls it apart, bites it open or drills it: saliva softens the shell and the radula scrapes the softened bit away. Monterey Bay Aquarium: Giant Pacific octopus
107 In many cephalopods, not just the blue-ringed octopus, a salivary gland produces a paralysing venom. Smithsonian Ocean: Octopuses, squids and relatives
108 In 1899 a Plymouth newspaper complained that common octopuses had become so abundant they had ‘quite ruined the fisheries’, eating crabs, lobsters and oysters. Smithsonian Ocean: Octopuses, squids and relatives
109 Sperm whales and seals eat octopuses and squid: scientists find their tough beaks in the whales’ and seals’ stomachs. Smithsonian Ocean: Octopuses, squids and relatives
110 Moray eels eat octopuses arm by arm, and dolphins toss octopuses against the water’s surface to stun them before eating. Smithsonian Ocean: Octopuses, squids and relatives

History and words

111 The oldest known octopus relative lived about 330 million years ago, long before the dinosaurs. Its fossil, from Montana, has ten limbs. Smithsonian Magazine: Ten wild facts about octopuses · checked 28 Oct 2026
112 Before that find, the oldest octopus fossil was Pohlsepia mazonensis, about 296 million years old, described as looking like a flattened ‘cow patty’. Smithsonian Magazine: Ten wild facts about octopuses
113 People have been fascinated by cephalopods for a long time: Aristotle wrote about them often, around 350 BC. Smithsonian Ocean: Octopuses, squids and relatives
114 Octopuses inspired sea monsters, from the Kraken of Nordic legend to the Caribbean’s Lusca. Smithsonian Magazine: Ten wild facts about octopuses
115 ‘Octopus’ comes from the Greek for ‘eight foot’. Smithsonian Magazine: Ten wild facts about octopuses
116 Merriam-Webster lists three plurals: octopuses, octopi and octopodes. Octopuses is now the most common. Merriam-Webster: octopus
117 ‘Octopi’ is the oldest plural, made on the mistaken idea that the word was Latin. It is really Greek, which is where ‘octopodes’ comes from. Merriam-Webster: octopus
118 The first known use of the word octopus in English was in 1759. Merriam-Webster: octopus