The reproductive pattern has a hard edge. A female blue-ringed octopus lays one clutch in her life. Counts center around fifty eggs, laid toward the end of autumn in the populations where this has been followed. She keeps the eggs under her arms and tends them for about six months. During that brooding she does not eat. When the eggs hatch, she dies.
That is semelparity, the one-time reproduction familiar from other octopuses, and it is as stark here as anywhere. The six months are not a figure of speech. Half a year of a one- or two-year life is spent as a guard that is slowly starving on purpose. The eggs are the entire future of that animal’s line, held in one basket, in one den, by one adult who will not get a second try.
The hatchlings do not stay to be parented. She is gone, and they go into the same shallow world as small versions of the hunter they will become. They carry, according to the research, toxin passed to them by the mother, so the eggs and the young are not a harmless stage. “Baby” is not a category that makes a blue-ringed octopus safe to handle. It is a smaller animal with the same general rules.
A brooding female in a shell is one of the easier animals to harm by accident. She will not flee in the ordinary way, because leaving is abandoning the clutch. Turning a shell over to admire it, in the right season and the right water, can be the end of fifty animals and of the mother who has already stopped feeding. Put the shell back the way you found it. Better, do not pick it up.