The Earth’s oceans are home to countless dangerous animals.
Octopuses are among the most scary-looking of all these underwater inhabitants.
Interestingly, these weird-looking tentacled monsters are not as dangerous as they appear.
In fact, only one species of octopus, the blue-ringed octopus, is venomous enough to cause considerable harm to humans that come in contact with it.
It has a bite that can kill a man in minutes.
However, there are several other venomous enigmas found under the sea.
In a recent study, it was found that virtually all octopus species had some amount of venom.
In this article, we’ll list 15 notable venomous octopus species with enough venom to cause harm to humans and other animals that cross their path.
15. Atlantic Pygmy Octopus
| Common name | Atlantic pygmy Octopus |
| Scientific Name | Octopus joubini |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 4.5 centimeters (1.8 inches) |
| Length | 9 centimeters (3.5 inches) |
| Weight | 30 grams (1.1 ounce) |
| Location | Waters of Australia and Tasmania |
As its common name suggests, Octopus joubini is a small octopus that inhabits the shallow waters of the Atlantic Ocean.
It is most commonly found in the tropical waters of the Gulf of Mexico and the Caribbean.
Despite the small size of this octopus (arms length of about nine centimeters (3.5 inches)), it is a prolific predator that preys specifically on shelled marine creatures such as clams and crustaceans.
This octopus has a strong radula that can drill holes into the hard shell of prey and inject the animal within with venomous saliva, paralyzing the prey.
The Atlantic pygmy octopus is generally shy and elusive, with a tendency to hide away in small crevices, empty clamshells, and empty cans under the water.
14. Day Octopus
| Common name | Day Octopus |
| Scientific Name | Octopus cyanea |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 16 centimeters (6.3 inches) |
| Length | Over 1 meter (3.3 feet) |
| Weight | 6 kilograms (13 pounds) |
| Location | Waters of Australia and Tasmania |
Octopus cyanea is also known as the big blue octopus, but it hardly retains this color for long.
Although camouflage is a common adaptation for octopuses, the day octopus is particularly adept at changing its color.
This octopus can also change the patterns or texture of its skin, helping it blend seamlessly within its environment.
Octopus cyanea changes color multiple times as it moves across the coral reef of the Pacific and Indian Oceans where it lives.
Another rare attribute of this octopus is its tendency to hunt during the day instead of at night, like most octopus species.
It kills prey by injecting them with toxic saliva before chomping down with its strong beaks.
A bite from this octopus may cause some discomfort and swelling, but it’s hardly problematic to humans.
13. Southern Sand Octopus
| Common name | Southern Sand Octopus |
| Scientific Name | Octopus kaurna |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 9 centimeters (3.5 inches) |
| Length | 42 centimeters (16 inches) |
| Weight | Unknown |
| Location | Waters of Australia and Tasmania |
Octopus kaurna is commonly referred to as the southern sand octopus because it tends to burrow into bottom sediments.
Unlike other octopus species that tend to bury themselves in shallow sediments to evade predators, the southern sand octopus creates a complex subsurface burrow where it can retract its entire body.
This species of octopus, native to southern Australia, has a venomous bite, which is effective against prey but not harmful to humans.
In fact, scientists are currently studying the venom of this cephalopod as a potential treatment for cancer and other chronic conditions.
12. Maori Octopus
| Common name | Maori octopus |
| Scientific Name | Macroctopus maorum |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 30 centimeters (11.8 inches) |
| Length | 1 meter (3.2 feet) |
| Weight | Up to 10 kilograms (22 pounds) |
| Location | Coast of New Zealand and Australia |
Macroctopus maorum, otherwise known as the Maori octopus, is one of the largest species of octopus native to New Zealand and Australia.
It is also one of the most aggressive octopus species.
The Maori octopus is known to attack other octopuses, including species larger than it in size.
The Maori octopus has a relatively mild venom that is effective against smaller animals but may not affect larger ones like humans.
The saliva of this octopus has a potent toxin that liquefies flesh and makes it easier for the octopus to digest.
A bite from this octopus may cause minor pain and swelling but are not typically life-threatening.
11. Caribbean Reef Octopus
| Common name | Caribbean reef octopus |
| Scientific Name | Octopus briareus |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 12 centimeters (4.7 inches) |
| Length | 60 centimeters (23 inches) |
| Weight | Up to 1.5 kilograms (3.3 pounds) |
| Location | Oceanic islands and the Pacific Ocean |
The Caribbean reef octopus is a specialized predator that traps prey by spreading its arm-like webbing to form a parachute.
Once caught, it uses its beak to tear prey apart.
The salivary papilla of this octopus can also inject venom into prey to paralyze them.
This venom is effective against small prey such as crabs, lobsters, shrimps, and various types of fish.
However, the venom is not strong enough to cause considerable damage to humans.
This octopus is found mainly in the open water and reefs of the oceanic islands and the Pacific Ocean.
10. California Two-Spot Octopus
| Common name | California two-spot octopus |
| Scientific Name | Octopus bimaculoides |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 17.5 centimeters (7 inches) |
| Length | 58 centimeters (23 inches) |
| Weight | Up to 1.5 kilograms (3.3 pounds) |
| Location | Pacific Ocean |
The California two-spot octopus (more commonly referred to as “bimac”) lives in the coastal waters of California and other parts of the Pacific Ocean.
The most distinctive feature of this octopus is the circular blue eyespots found on each side of its head.
The common name of this octopus refers to these two spots.
The main prey of the California two-spot octopus include snails, bivalves, limpets, and crustaceans, which they hunt through ambush and camouflage.
Once it catches prey in its tentacles, this octopus injects a toxic venom that affects the animal’s nervous system and paralyzes it.
However, the venom does not seem to have any adverse effect on larger predators and humans.
9. Common Octopus
| Common name | Common octopus |
| Scientific Name | Octopus vulgaris |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 25 centimeters (10 inches) |
| Length | 1 meter (3.3 feet) |
| Weight | 3–10 kilograms (6.6–22 pounds) |
| Location | Worldwide |
True to its name, the common octopus is quite common and well-known.
It is found in every ocean all over the world, including tropical, subtropical, and temperate waters.
Octopus vulgaris has an average mantle length of about 25 centimeters (10 inches), and its tentacles can grow to an average length of about one meter (3.3 feet).
Although more famous for its intelligence, the common octopus is a mean little creature.
It feeds by breaking into the shells of shelled animals with its strong beak and injecting them with a strong venom to subdue them.
Even members of their species are not excluded from their onslaught, and mating often ends in cannibalism for these octopuses.
8. Giant Pacific Octopus
| Common name | Giant Pacific octopus |
| Scientific Name | Enteroctopus dofleini |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 60 centimeters (2 feet) |
| Length | 6 meters (20 feet) |
| Weight | 10–71 kilograms (22–156 pounds) |
| Location | North Pacific Ocean |
The giant Pacific octopus has an average span of up to six meters (20 feet) and may weigh as much as 15 kilograms (33 pounds).
Each tentacle of this giant octopus can be up to 14 feet long, and they have numerous giant suckers that can lift weights of up to 16 kilograms (35 pounds) each.
It is considered the largest octopus species in the world.
Enteroctopus dofleini feeds on a diet of shrimp, crabs, snails, clams, and other shelled animals, but it may also eat fish, squid, and other soft-bodied prey.
This giant octopus is even large enough to prey on other octopuses.
In addition to using its massive suckers and muscular tentacles to grab prey, the giant octopus can also release toxic venom to incapacitate prey before devouring them.
As scary as the idea of a giant venomous octopus might sound, the venom of Enteroctopus dofleini isn’t strong enough to cause significant harm to humans.
7. Poison Ocellate Octopus
| Common name | Poison ocellate octopus |
| Scientific Name | Amphioctopus mototi |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 10 centimeters (4 inches) |
| Length | 50 centimeters (20 inches) |
| Weight | Unknown |
| Location | South Pacific |
The dramatic name of this octopus is enough to tell you how potentially lethal this creature is.
Amphioctopus mototi is sometimes referred to as ‘fe’e mototi’ by locals on the Rapa Island of the South Pacific, where it is quite common.
Some people also refer to it directly as the “poison octopus.”
Despite the fear-inducing name, the poison octopus’ venom is mainly reserved for prey.
It is a formidable predator that preys on shellfish and hermit crabs by drilling into their shell and injecting venomous saliva that paralyzes their prey, making it easier to extract them from their shell.
This octopus is a natural orange-brown color but will start flashing maroon stripes over a white background when it feels threatened to warn off potential predators.
6. Coconut Octopus
| Common name | Coconut octopus |
| Scientific Name | Amphioctopus marginatus |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 8 centimeters (3 inches) |
| Length | 15 centimeters (6 inches) |
| Weight | 200–400 grams (7–14 ounces) |
| Location | Western Pacific Ocean |
Amphioctopus marginatus got its common name from its bizarre habit of carrying half of a coconut shell around.
This octopus species uses the coconut shell as a sort of make-shit shell when it needs to evade predators while it walks around on two legs.
It sometimes looks like a floating coconut as it moves around in the warm tropical waters of the Western Pacific Ocean where it lives.
Although it is not considered dangerous to humans, this octopus species is known to be capable of delivering a painful bite and can inject venom.
Amphioctopus feeds on shrimp, crabs, clams, and other small marine animals.
5. The Mimic Octopus
| Common name | The mimic octopus |
| Scientific Name | Thaumoctopus mimicus |
| Venom level | Not enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 5.8 centimeters (2.2 inches) |
| Length | 60 centimeters (2 feet) |
| Weight | 2.3–9.1 kilograms (5–20 pounds) |
| Location | Indo-Pacific Ocean |
The mimic octopus (Thaumoctopus mimicus) isn’t any more dangerous to humans than other octopus species.
The venom of this Indo-Pacific cephalopod can’t cause significant damage to humans or protect it against large predators in its habitat.
To protect itself against predators, the mimic octopus relies on its ability to take on the shape and form of other animals.
So, in addition to being mildly venomous, this octopus deserves a spot on this list for its ability to look more venomous than it really is.
Although several other animals use mimicry to evade predators, most of them can only mimic one animal.
Thaumoctopus mimicus is a shape-shifting octopus that can take on the form of several animals and do so rapidly if necessary.
4. Seven-Arm Octopus
| Common name | Seven-arm octopus |
| Scientific Name | Haliphron atlanticus |
| Venom level | Enough to kill a man (jellyfish sting) |
| Diet | Carnivorous |
| Mantle length | 0.69 meters (2.3 feet), a total length of 2.90 meters (9.5 feet) |
| Length | 2.90 meters (9.5 feet) |
| Weight | 75 kilograms (165 pounds) |
| Location | Atlantic Ocean |
Contrary to what its name might suggest, the seven-arm octopus has eight tentacles like other octopus species.
This octopus species was given this name due to a unique modification in one of its tentacles, which forms a specialized organ used for fertilization in males, known as the hectocotylus.
The seven-arm octopus is the second-largest octopus species in the world.
Like many other octopuses, Haliphron atlanticus has a mild venom that can hardly harm humans.
What makes this octopus particularly dangerous is its symbiotic relationship with some species of jellyfish.
The poisonous stingers of the jellyfish often found in association with the seven-arm octopus provide an extra layer of defense that’s even more toxic than its own venom.
3. Southern Blue-Ringed Octopus
| Common name | Southern blue-ringed octopus |
| Scientific Name | Hapalochlaena maculosa |
| Venom level | Enough to kill a man |
| Diet | Carnivorous |
| Mantle length | 5.7 centimeters (2.2 inches) |
| Length | 7 to 10 centimeters |
| Weight | 28 grams (0.062 pounds) |
| Location | Pacific and Indian Ocean |
Hapalochlaena maculosa (more commonly known as the blue-ringed octopus) is one of the smallest octopus species in the world.
Ironically, it happens to be one of the most dangerous octopuses, too, and arguably one of the most venomous animals ever discovered.
The average length of this octopus is about 12 to 20 centimeters (5 to 8 inches) — smaller than the size of some of the biggest spider species.
Despite its small size, the powerful neurotoxin (tetrodotoxin) that this octopus carries can kill a human in mere minutes.
Fortunately, the blue-ringed octopus is docile and rarely attacks humans.
In fact, it’ll pulse its beautiful blue rings as a warning if it ever feels threatened.
This octopus is found in the shallow waters of the Pacific and Indian Oceans, where it hides itself in rock crevices.
2. Blanket octopus
| Common name | Blanket octopus |
| Scientific Name | Tremoctopus |
| Venom level | Enough to kill a man (jellyfish sting) |
| Diet | Carnivorous |
| Mantle length | 18–25 centimeters (7.1–9.8 inches) |
| Length | 2 meters (6.6 feet) |
| Weight | Up to 10 kilograms (22 pounds) in female species |
| Location | Indo-West Pacific Ocean |
The blanket octopus (Tremoctopus) is not venomous in itself but deserves a top spot on this list because of the ingenuity of its defensive strategy.
This octopus is one of the few animal species immune to the venom of the Portuguese man o’ war, a dangerous jellyfish whose sting has been known to kill humans.
The blanket octopus takes “bizarre” even further by ripping off the tentacles of the jellyfish and carrying them with it to stab prey and predators.
The Tremoctopus intimidates predators by stretching out its arms to create a blanket-like silhouette that makes it look bigger than it really is.
Females are generally bigger (up to two meters (6.6 feet) in length), while males are less than an inch long.
1. Greater Blue-Ringed Octopus
| Common name | Greater blue-ringed octopus |
| Scientific Name | Hapalochlaena lunulata |
| Venom level | Lethal (enough to kill a man) |
| Diet | Carnivorous |
| Mantle length | 3–5 centimeters (1.2–2 inches) |
| Length | 12–15 centimeters (4.7–5.9 inches) |
| Weight | 80 grams (0.2 pounds) |
| Location | Indo-West Pacific Ocean |
As the name suggests, the greater blue-ringed octopus is a slightly bigger close cousin of the regular blue-ringed octopus.
It is still generally small compared to other octopuses, with an average diameter of seven to eight millimeters.
The greater blue-ringed octopus has venom glands connected to its salivary glands and beak.
This gland produces the venom tetrodotoxin (TTX), one of the world’s most dangerous toxins.
Only two milligrams of this toxin is enough to kill a man in mere minutes.
Even worse, the greater blue-ringed octopus delivers a painless sting, so people who get bitten may not know until it’s too late.
The flashes of iridescent rings is a warning signal that’s best heeded by humans and predators.
Sources:
- https://oceanfauna.com/coconut-octopus/
- https://en.wikipedia.org/wiki/Blue-ringed_octopus
- https://www.americanoceans.org/facts/are-giant-pacific-octopus-venomous/
- https://animaldiversity.org/accounts/Octopus_bimaculatus/#42C08A51-7BE8-11E2-83AC-002500F14F28
- https://octonation.com/caribbean-reef-octopus-facts/#:~:text=They%20use%20their%20beaks%20and,helping%20to%20paralyze%20their%20prey.
- https://octonation.com/octopedia/southern-sand-octopus/
- https://www.islandventure.com/octopus/
- https://en.wikipedia.org/wiki/Seven-arm_octopus
- https://en.wikipedia.org/wiki/Mimic_octopus
