Octopuses Use Venom for Safe Sex, Biologists Reveal

Humans are not the only species who practice ‘safe sex’, although this means something quite different for one species of octopus.

Marine biologists from Australia have revealed that male-blue lined octopuses (Hapalochlaena fasciata) deliver a precise venomous bite to females before mating.

And why? Because the females of the species tend to be twice the size of the males—and prone to eating their lovers if given a chance.

“Envenomating the females renders them immobile, enabling the males to mate successfully,” the researchers explained in their paper.

The venom used by the blue-lined octopus is “tetrodotoxin”—perhaps most famously known as the deadly poison found in pufferfish, whose meat is considered a delicacy but which can kill if not prepared properly.

Tetrodotoxin is capable of paralyzing prey, and in laboratory mating experiments the researchers observed that male blue-lined octopuses use a bite to inject tetrodotoxin-laden saliva into their mates’ aortas to escape being cannibalized.

The venom used in this gambit is not produced by the octopus itself, but is derived from symbiotic bacteria that live within its body.

Monitoring the breathing rates of both male and female octopuses during mating, the team report that the females’ rate tended to drop off sharply when mating began, ceasing altogether after around eight minutes.

“In this asphyxia-like state, the female body color turned pale. The pupils also constricted, losing all reflexes to bright light flashes, symptomatic of a loss of nerve control such as during tetrodotoxin envenomation,” the researchers noted.

“Once the females were immobilized, the males successfully copulated and mating ended when the females regained control of their arms and pushed the males off.”

None of the females in the experiments died from the males’ bites, which suggests they have some degree of resistance to the toxin—a vital capacity for species which use venom to subdue prey and so risk accidentally envenomating themselves.

Despite this, however, the females did not emerge unscathed; swollen humps and open wounds were spotted at the site of their bites post-mating. Regardless, all females observed in the study went on to lay eggs within 3 to 29 days.

This venom-assisted mating strategy is not unique to blue-lined octopuses. Many smaller male octopus species have also evolved other means to mitigate the dangers of sexual cannibalism. Some, for instance, use an elongated, modified arm to transfer sperm into their mates from a distance, minimizing the risk of being devoured by larger females.

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Reference

Chung, W.-S., Kurniawan, N. D., Marshall, N. J., & Cortesi, F. (2025). Blue-lined octopus Hapalochlaena fasciata males envenomate females to facilitate copulation. Current Biology, 35. https://doi.org/10.1016/j.cub.2025.01.027