According to National Geographic, the common octopus preys on crabs, crayfish and molluscs. Bottom-dwelling octopuses feed mainly on polychaete worms, crabs, whelks and clams. Open-ocean octopuses subsist on prawns, fish and other cephalopods. The giant Pacific octopus feeds on shrimp, clams, lobsters and fish, and even larger prey, such as sharks and birds.
Octopuses hunt at night and usually inject their pray with a paralysing saliva before using their sharp beak to dismember them into small pieces. To access the meat of shelled creatures, octopuses sometimes drill a hole into the shell and inject a secretion through the hole before extracting the mollusc's soft body. Sometimes the shells can be pried open using force.
Octopuses are known for their intelligence and problem-solving skills, and it is believed they are the smartest of all invertebrates, according to About.com. They have unique defense mechanisms, with the most frequently used being their ability to hide with camouflage. This allows an octopus to match the colors, patterns and textures of its surroundings. Octopuses also have the ability to squirt a thick cloud of ink, and escape very quickly using jet-like propulsion. Because they have soft, boneless bodies, octopuses are able to manipulate themselves to fit into very small crevices and cracks.