Diving With Octopuses: How to Find Their Dens, Read Their Behavior, and Watch Without Disturbing Them

Most divers remember their first octopus. It might have been a pair of eyes watching from a crack in the reef, or a patch of "rock" that suddenly changed color and slid away across the sand. Octopuses live in every ocean, from tropical reefs to cold kelp forests, yet they are easy to swim past because they are built not to be noticed. Once you learn what an octopus den looks like and when these animals come out, you will start finding them on dives where you never saw one before.

This guide covers how octopuses work, the species recreational divers are most likely to meet, how to find a den, how to read an octopus's body language, and how to watch and photograph one without causing it stress.

What Makes an Octopus Different

Octopuses are cephalopods, the group of mollusks that also includes squid, cuttlefish, and the nautilus. About 300 octopus species have been described. They have no internal or external shell; the only hard part of the body is a parrot-like beak at the center of the arms. That is why an octopus can squeeze through a gap only slightly larger than its beak, and why a den entrance can look far too small for the animal living inside it.

A few other traits are worth knowing before you go looking:

• Three hearts and blue blood. Two hearts pump blood through the gills and a third pumps it to the rest of the body. Their blood uses a copper-based protein, hemocyanin, to carry oxygen, which gives it a blue color.
• A distributed nervous system. An octopus has roughly 500 million neurons, and about two-thirds of them are in the arms rather than the central brain. Each arm can explore and respond to what it touches with a good deal of independence.
• Suckers that taste. The suckers carry chemical receptors, so an octopus probing a crevice is effectively tasting what it touches. This is how it finds crabs and shellfish hidden out of sight.
• Short lives. Many species live only a year or two. The giant Pacific octopus lives longer, often three to five years. Most octopuses breed once at the end of life. The female guards and cleans her eggs, usually without eating, and dies soon after they hatch.

That brooding period can be remarkable. Researchers from the Monterey Bay Aquarium Research Institute watched a deep-sea octopus, Graneledone boreopacifica, guard a single clutch of eggs for 53 months, the longest brooding period recorded for any animal.

Camouflage: Why Octopuses Are So Hard to Spot

An octopus can change color, pattern, and even skin texture in a fraction of a second. Its skin holds thousands of chromatophores, small elastic sacs of pigment that muscles stretch open or squeeze shut under direct control of the nervous system. Beneath them, reflective cells called iridophores and leucophores add shimmer and white tones. Small muscles can also raise bumps and spikes called papillae, turning smooth skin into something that looks like algae-covered rock or coral.

Most octopuses are thought to have only one type of visual pigment, which would make them colorblind in the usual sense, yet they still blend closely into their surroundings. How they manage it is an open research question, and one more reason they reward patient observation.

For divers, this means you will rarely find an octopus by scanning for its shape. You find it by reading the reef for signs that one lives there.

How to Find an Octopus on a Dive

Look for the Midden

The single best clue is a midden: a small pile of empty shells and crab parts outside a hole. Octopuses carry prey back to the den, eat, and push the leftovers out the door. Fresh clam and snail shells, crab carapaces, and claws heaped beside a crevice are a strong sign that someone is home. On sandy or muddy bottoms, look for a hole with shells, stones, or debris pulled across the entrance like a door.

Search the Right Habitat

Octopuses need shelter. Check rock piles, ledges, coral heads with deep cracks, jetties, pier pilings, and the edges of reef where it meets sand. At muck diving sites, they also move into discarded bottles, cans, and shells. Scan slowly and look for things that seem slightly out of place: an eye with a horizontal, bar-shaped pupil, the curl of an arm tip, or a patch of rock with a texture that doesn't quite match its neighbors.

Time Your Dive

Many species hunt at dusk and at night and spend the day tucked into their dens. A dusk dive or a slow night dive is often the most productive way to see octopuses out in the open, crawling across the bottom and hunting. A few species break this rule. The day octopus (Octopus cyanea) of the Indo-Pacific and Hawaii does much of its hunting in daylight, often trailed by fish waiting to grab prey it flushes out.

Use a Narrow-Beam Light

A focused handheld light is the most useful tool for octopus spotting, even on a bright day. It lets you look deep into cracks and under ledges without flooding the whole area with light, and it brings back the reds and oranges that water absorbs at depth. Aim the soft edge of the beam at the animal, not the bright center, and move it off the octopus once you have had a look. Our guide on how to choose a dive light explains lumens and beam angle in more detail. The BigBlue 1300 Lumen Narrow Beam is well suited to this kind of searching.

On dusk and night dives, carry a second light in case your primary fails. A compact, narrow-beam backup such as the SeaLife Sea Dragon Mini 900S clips to your BCD and doubles as a focus light when you want to check a crack without lighting up your buddy. You can compare more options in our dive lights collection.

Octopus Species Divers Commonly See

Caribbean Reef Octopus

The Caribbean reef octopus (Octopus briareus) is found from Florida through the Caribbean. It is mostly nocturnal and is a common sight on night dives, often in a blue-green color with reddish-brown mottling. It tends to hunt by spreading its arms and the web between them over a coral head or rock, trapping prey underneath.

Day Octopus

The day octopus (Octopus cyanea), known in Hawaii as he'e, ranges across the Indo-Pacific and the Red Sea. Because it hunts in daylight, it is one of the easiest octopuses to watch in action. Researchers filming this species in the Red Sea have documented it hunting in mixed groups with goatfish and groupers, with the octopus occasionally punching a fish out of the way.

California Two-Spot Octopus

Southern California divers often meet the California two-spot octopus (Octopus bimaculoides), named for the blue, ring-like eyespots below each eye. It lives in rocky reefs and kelp forest habitat. Our guide to California's kelp forests covers more of what lives on these reefs.

Giant Pacific Octopus

The giant Pacific octopus (Enteroctopus dofleini) lives in the cold North Pacific, from California to Alaska and across to Japan. Adults commonly weigh around 15 kg (33 lb), and the largest have arm spans of about 4 m (14 ft). Puget Sound and British Columbia are among the most reliable places to dive with them. After a legal harvest at a popular West Seattle dive site drew public backlash in 2012, Washington prohibited recreational harvest of giant Pacific octopus at seven well-known Puget Sound dive sites starting in 2013, so that divers have a better chance to see them.

Mimic, Wonderpus, and Coconut Octopuses

Muck diving destinations such as the Lembeh Strait in Indonesia and Anilao in the Philippines are known for unusual species. The mimic octopus (Thaumoctopus mimicus), first scientifically documented off Sulawesi in 1998, can impersonate lionfish, flatfish, and sea snakes. The wonderpus (Wunderpus photogenicus) is a long-armed, white-striped relative formally described in 2006. The coconut octopus (Amphioctopus marginatus) gathers coconut and clam shell halves and carries them across the sand for later use as shelter, behavior that researchers described as tool use in 2009.

Blue-Ringed Octopuses: Look, Never Touch

Blue-ringed octopuses (genus Hapalochlaena) live in tide pools and shallow reefs across the western Pacific and Indian Ocean, from Japan to Australia. They are small, often no larger than a golf ball in body size, and display bright blue rings when alarmed. Their saliva contains tetrodotoxin, a nerve toxin that can cause paralysis and respiratory failure. There is no antivenom; treatment is supportive, including rescue breathing until medical help takes over. Bites are rare and almost always happen when someone picks one up. For more on animals that should be observed and never handled, see our guide to marine life divers should never touch.

Reading Octopus Body Language

An octopus's skin is a running display of how it feels about you. Learning a few signals helps you know when to stay and when to back off.

• Calm and curious: The octopus stays in or near its den, watches you, and may reach an arm tip toward you or your light. Color shifts are slow and match the background. This is a good time to hold still and let it decide how close to come.
• Uneasy: It pulls deeper into the den, flattens its body, or goes very pale or very dark. Rapid color flickering or waves of dark color passing over the body often signal agitation. Give it more space.
• Stressed or threatened: It jets away, inks, or spreads its arms and web wide to look larger. Ink is made of melanin and can form either a cloud or a dense blob, called a pseudomorph, that acts as a decoy while the octopus escapes. If an octopus inks at you, you were too close or moving too fast. End the encounter and move on.

Octopus Etiquette: How to Watch Without Disturbing

An octopus that feels safe will often come out and investigate on its own, which is a far better encounter than anything you can force. These habits protect the animal and improve what you see.

• Never pull an octopus from its den or block the entrance. The den is its main defense against predators. Hover outside and let it stay in control of whether it comes out.
• Don't touch, chase, or herd it. If an octopus reaches out and touches you, stay still and let it explore, then let it withdraw on its own terms. Don't grab back, and don't follow one that is moving away.
• Don't feed octopuses. Feeding changes their natural behavior and can draw them into the open where predators find them.
• Keep lights brief and indirect. Use the edge of your beam, take your look or your shots, and then move the light away. On night dives, some divers switch to a red light for longer observation, since many marine animals appear to react less to red light.
• Stay off the bottom. Den sites are often silty or surrounded by fragile life. Hover with neutral buoyancy and use a frog kick. If you keep sinking toward the sand, our scuba weighting guide can help, and our low-impact diving tips cover reef-safe technique.
• Leave brooding females alone. If you see strings of small, teardrop-shaped eggs hanging from the ceiling of a den, the female is guarding her last clutch. Look briefly, keep lights off her, and move on.
• Know local rules. Octopus harvest is regulated differently from place to place, and some dive sites and marine parks prohibit it entirely. Check the regulations for wherever you dive.

Photographing Octopuses

Octopuses make excellent photo subjects because they often stay in one spot and respond to a patient diver. Get low and shoot at eye level rather than down from above; the eye is the focal point of the image. Approach slowly, take a few frames, then back off and wait. A relaxed octopus often comes partway out of its den after a minute or two, which will give you a better picture than pushing closer. Place your light slightly off to the side of the lens to cut down on backscatter; our backscatter and strobe positioning guide walks through the angles.

A simple setup works well for octopus photography. The SeaLife Micro 3.0 Pro Dual Beam Set combines a sealed camera with a light that switches between a wide flood for shooting, a tight spot for searching dens, and red LEDs for night dives when you want to observe without bright white light.

For exposure settings, see our manual mode camera settings guide, and browse compacts, housings, and lights in our underwater cameras collection.

Share Your Sightings

Your octopus photos can help researchers. Uploading them to iNaturalist with the date, depth, and location adds to records of where species live and how their ranges change, and the community can often help confirm an ID. In Puget Sound, the Seattle Aquarium has organized an annual octopus survey with volunteer divers for more than two decades. Our guide to becoming a citizen science diver lists other programs worth joining.

Octopus Spotting Checklist

• Search rock piles, ledges, coral cracks, pilings, and reef edges.
• Look for middens: piles of shells and crab parts outside a hole.
• Plan a dusk or night dive for most species.
• Carry a narrow-beam primary light and a backup.
• Use the edge of the beam and keep light time short.
• Hover neutrally and stay off the bottom.
• Never pull an octopus from its den, block it in, or feed it.
• Back off at the first sign of stress: rapid color changes, flattening, or ink.
• Never touch a blue-ringed octopus.
• Log your sighting with location, depth, and date.

Octopuses reward the same habits that make you a better diver everywhere: slow movement, good buoyancy, a light in hand, and the patience to let an animal come to you.