Octopuses which belong to invertebrates or animals lacking a backbone are known to have uncanny intelligence and supernatural abilities to change body color and restore their limbs. However, they often die of bizarre behavior that seems to destroy themselves after their first breeding.

“What causes this mysterious behavior of octopuses is related to changes in steroid hormone secretion, and octopuses work as a system that destroys themselves after breeding,” Dr. Jang Wang of the University of Chicago said in a thesis published in the scientific journal Current Biology. Researchers who analyze California’s two-spot octopuses bred in the laboratory found: Female octopuses were actively going around and hunting for food before mating, but their behavior changed after laying eggs. Sitting in a pile of eggs, they did the act of supplying oxygen and were very wary of access from other animals. After three or four days, they almost stopped their short feeding activities to eat crabs passing around the eggs and began focusing only on caring for their eggs. In around 10 days since then, these female octopuses gradually lost their physical strength. 

By the time baby octopuses hatched from eggs, mother octopuses were approaching death. They became very tired and weak, and the time they left from the eggs was getting longer. The researchers said, “The octopus, which lost its pale skin color and elasticity, cut off its legs as if urging the process of death.”

Why do octopuses act like this? Researchers said that there are two most plausible hypotheses. One is a hypothesis that they happened to have a system of preventing themselves from threatening their own species’ survival due to their excruciatingly strong predatory tendencies among their peers. The other one is that they wanted to prevent a few number of octopuses excessively grown from preying on young octopuses.  

Praising the study, Roger T. Hanlon, senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts told, “This is an elegant and original study that addresses a longstanding question in the reproduction and programmed deaths of most octopuses.”  The action of destroying themselves by octopuses is bizarre as animals like them which have large brains tend to live longer.

Dr. Jo Seon-mi at the Marine Biodiversity Institute of Korea has been conducting basic research about it, including brain structure of octopuses. She said, “It is an interesting study that has found the behavioral mechanism of mother octopuses dying while caring for eggs from a steroid hormone perspective.” There are many hypotheses from scientists about the phenomenon that octopuses die of self-harm after laying eggs.