Male octopuses inject females with venom during sex to avoid being eaten, according to a recent study. The blue-lined octopus is a small yet potentially dangerous marine creature due to its potent neurotoxin, tetrodotoxin (or TTX). This species faces a significant size disparity between males and females, with females growing roughly twice as large as males, posing a cannibalistic threat during mating.

To counter this danger, male blue-lined octopuses have developed a survival strategy: they deliver a precise bite near the female's aorta, injecting TTX and temporarily paralyzing her before attempting to mate. This behavior is particularly notable as many octopus species exhibit sexual dimorphism and instances of females cannibalizing smaller males, leading to the evolution of various male survival tactics such as elongated mating arms or the ability to detach an arm to facilitate escape. However, blue-lined octopuses lack these features, making their venomous bite a crucial adaptation.

Both sexes have TTX in their saliva for predation and defense, but males have disproportionately larger posterior salivary glands, where the toxin is produced. This suggests a co-evolutionary link between protection, predation, and mating success in males.

Tank observations showed that females quickly became immobilized after males clasped them, displaying breathing cessation, paleness, constricted pupils, and loss of reflexes, indicating TTX envenomation, though none died. After regaining control, the females pushed the males away, and small, swollen lumps with wounds near their aortas confirmed the venomous bite.


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