Biology/Natural History: The 3rd right arm of the male of this species has a large hectocotylus, about 1/5 the length of the arm (photo). The hectocotylus is used in transferring the male's spermatophore, or package of sperm, which may be up to a meter long, to the female. The hectocotylus may be left within the mantle of the female during the process. Eggs, which look like small whitish grapes, are laid throughout the year but mainly in the winter. When the female has eggs she attaches them to the roof of a cave and guards them until they hatch (5-7 months). She may lay 35,000 to 70,000 eggs in a single clutch. Hatching is mainly in early spring, and the young are pelagic for one to several months before settling. The young are sometime seen swimming near the surface. Lifespan is thought to be 4-5 years. Prey include crustaceans (shrimp and crabs), mollusks (scallops, clams, abalones, moon snails, small octopus), and fish (rockfish, flatfish, sculpins). The octopus are often captured in crab traps, where they are trying (successfully) to steal the crabs. Females can be cannibalistic. The Seattle Aquarium recently observed an octopus catching the spiny dogfish Squalus acanthias, and in 2005 we found the picked-clean skeleton of a dogfish on the shellheap outside an octopus den (photo). The species accumulates a large pile of shells and crab carapaces outside the den, which is usually under a boulder or in a rocky crevice. They quickly kill crabs by rasping a tiny hole (1 mm or less in diameter) through the carapace (photo), probably with their radula, then presumably injecting poison, perhaps with their beak. Several species may be attracted to their shell pile (midden), including Pycnopodia helianthoides and the snail Amphissa columbiana. Predators include seals, sea otters, dogfish sharks, lingcod, and man. Parasites include the mesozoans Dicyemenna abreida and Conocyema deca, which live in the kidney.
This octopus is said to be capable of inflicting a painful bite but I have never seen anyone bitten, even when wrestling them off the rocks. They seem much less ready to bite than is O. rubescens.