Octopuses have fascinated both scientists and laypeople for a long time, and it seems they only become more intriguing with each discovery. They're incredibly intelligent, have three hearts, eject ink, have blue blood, grow new arms, are master disguisers, and fit into the tiniest of places. But one aspect of the octopus life cycle has perplexed scientists for decades. Why do mother octopuses starve themselves to death?
Female octopuses are energetic hunters during their lifetime, actively praying on crabs and other sea creatures unlucky enough to get too close. However, something peculiar happens once they lay their eggs. For the first three or so days, the mother octopus will continue to feed, although always close to her eggs. But as more days go by, she stops eating, starving herself to death. Alarmingly, some female octopuses even speed this process up, opting to slam themselves into nearby rocks or over-grooming their tentacles to the point of injury. As a result, the final days of a female octopus's life are painful, bleak, and joyless.
In 1977, researchers at Brandeis University in Massachusetts proved that this strange behavior would cease by removing the optic gland from female two-spot octopuses.1 The optic gland in octopuses functions similarly to the pituitary gland in other animals; it's responsible for hormone secretion and regulation.
When the gland, which sits between the octopus's eyes, is removed, the female octopus would continue feeding, abandon their eggs, and some even went on to mate again. This is particularly interesting because octopuses are semelparous animals, meaning they only reproduce once in their lifetime and then die shortly afterward.
More recent studies into the optic gland have managed to map precisely how the female octopus's behavior changes after they mate. Although further testing is needed, it appears that an influx of steroids and insulin-type hormones could be responsible for promoting maternal behavior and directing energy away from life-sustaining activities like eating.2
Despite decades of research into how this process takes place, one question remains. Why exactly have octopuses evolved to behave this way? Although there's no definitive answer, several theories exist.
The majority of octopus species practice cannibalism. Sexual cannibalism, where a female octopus eats the male during mating, has been well documented. However, in recent years, other types of cannibalism have been observed. For example, in Spain, divers managed to find an octopus den in which a male octopus was dining on an already dead, much smaller octopus.3
Their cannibalistic nature is also why octopuses are challenging to raise in captivity - they need separate tanks to ensure some don't end up becoming a meal.
The primary goal of evolution is to select traits that ensure organisms pass on their genes to the next generation. With this in mind, some scientists have theorized that perhaps female octopuses evolved this trait to ensure they didn't eat their young. But, of course, there would be no next generation of mother octopuses who ate their offspring.
In the wild, octopuses have short life spans, with some species only living around six months. In the 1977 study into optic gland removal, scientists proposed that maybe octopuses have a forced short lifespan to prevent their numbers from quickly getting out of hand. If the ecosystem becomes overpopulated with octopuses, there won't be enough food to go around.
While scientists aren't yet clear on the exact reason female octopuses starve themselves to death, it's clear that this behavior is pre-programmed and likely aids the survival of the species in some way.