What Do Giant Pacific Octopuses Eat? Crabs, Clams and Dens

What is on the menu?

The giant Pacific octopus is a generalist predator: it eats almost any animal it can catch and overpower. Studies of food remains in different parts of its range show that the mix varies from place to place, but two groups usually dominate.

• Crabs: often the most important prey near rocky reefs. The red rock crab is a favorite in Puget Sound, and many other crabs are taken where they are common.
• Clams and other bivalves: clams, cockles, mussels and scallops, especially where the seabed has sand or mud for digging.
• Snails and abalone: taken from rocks and kelp.
• Shrimp and lobster-like crustaceans: smaller but frequent prey.
• Fish: caught mostly when they rest on the bottom or shelter in crevices.
• Squid and octopuses: including smaller giant Pacific octopuses.

Where the seabed is soft and full of clams, octopuses often choose dens in the sediment nearby; where crabs are plentiful, they tend to den among rocks. In other words, the octopus’s home is partly chosen around its food.

Surprising prey: sharks and seabirds

Giant Pacific octopuses occasionally take animals that seem far too big or too fast for them. In aquariums they have caught and eaten spiny dogfish, small sharks up to about 1.2 m (4 ft) long, that shared their tanks. The remains of spiny dogfish have also been found in middens outside wild dens, which suggests that wild octopuses catch them too.

In 2012 an amateur photographer recorded a wild giant Pacific octopus seizing a gull and pulling it underwater. Events like this are rare, but they show that the octopus will try almost anything within its size range.

How does a giant Pacific octopus hunt?

A giant Pacific octopus usually leaves its den at night or in the early hours, though it can forage by day. It hunts with its eyes, which are sharp, and with its arms, whose suckers carry thousands of chemical receptors. An octopus can literally taste a crab hiding in a crack before it sees it.

It uses several techniques:

• Probing: it pushes its arm tips into crevices, under rocks and into the sediment, grabbing anything edible it touches.
• Pouncing: it leaps on prey and spreads its arms and web over it like a net, trapping the animal underneath.
• Stalking and ambush: it creeps toward prey while camouflaged, changing color and skin texture to blend with the bottom, then strikes.
• Digging: it uses its arms and jets of water to excavate buried clams.

Captured prey is held by the suckers and brought to the mouth, at the center of the arms, where a hard beak bites through flesh and shell.

How does it open shells?

Hard shells are no great obstacle. An octopus has three main ways to reach the meat inside:

1. Pulling: strong suckers on several arms grip both halves of a clam or mussel and pull until the muscle holding the shell shut gives way.
2. Breaking: the beak, made of tough chitin, can chip or crack thinner shells and crab claws.
3. Drilling: the octopus grinds a tiny hole through the shell, using its radula, a ribbon of minute teeth, and the salivary papilla, a small toothed organ near the beak. It then injects saliva containing toxins and enzymes that paralyze the prey and loosen the flesh.

Drill holes are small and neat, so scientists can tell from an empty shell whether an octopus drilled it. Octopuses seem to switch between methods depending on the prey and on how hard it is to pull open.

Dens and middens: how divers find octopuses

After hunting, the octopus usually carries its catch back to its den and eats there, out of sight of predators such as harbor seals and sea otters. The leftovers are pushed out of the entrance and pile up as a midden, a heap of crab carapaces, claws, clam shells and snail shells.

Middens are the easiest way to spot a den. Divers in British Columbia and Washington look for a fresh pile of shells at the base of a boulder or the mouth of a dark hole; if the shells are clean and recent, an octopus is probably at home. Scientists sort and identify the shells in middens to study diet without disturbing the animals, though remains of soft-bodied prey, such as fish, are underrepresented because little is left over.

How do young octopuses and mothers eat?

A giant Pacific octopus hatches about the size of a grain of rice and spends its first one to three months drifting in the plankton. At this stage it eats tiny animals, such as the larvae of crabs and other small crustaceans. Once it settles on the seabed it switches to small crabs, shrimp and bivalves, and its prey grows with it.

Growth is fast: the octopus gains close to 1 percent of its body weight every day and can reach tens of kilograms in a few years, as explained in how big is a giant Pacific octopus? Because it is cold-blooded, much of the food it eats goes straight into growth rather than into keeping warm.

The one time a giant Pacific octopus stops eating is at the end of its life. A brooding female guards her eggs for about five to seven months without leaving to hunt, living off her own body until she dies around the time they hatch. Males also lose their appetite after mating.

Does diet differ from other octopuses?

The basic diet of crabs and clams is shared by most shallow-water octopuses. The common octopus of Europe also eats crabs, clams and mussels, drills shells and builds middens. The giant Pacific octopus differs mainly in scale: its size lets it tackle larger crabs, bigger clams and occasionally sharks and seabirds that smaller octopuses could never subdue. Its intelligence also helps. Octopuses learn which prey is easiest to open and remember good hunting areas, a topic covered in how smart are octopuses?