“In the wild, octopuses can hide in shells, human discards such as beer bottles, crevices, and under rocks. They do not find the ‘ideal’ home in terms of characteristics such as volume and aperture area, but instead modify shelter by clearing out sand and rubble, detaching algal fronds, and bringing rocks to block the aperture. Many octopus species are likely limited in the wild by the availability of shelter.” (p. 20)
Mather, M. & Scheel, D. (2014). Behavior. In J. Iglesias, L. Fuentes, & R. Villanueva (Eds.) Cephalopod culture (p. 17-39). New York: Springer.