Male blue-lined octopi (Hapalochlaena fasciata) have been found to use venom on their sexual partners, as well as for the usual reasons of defense against predators and subduing prey. Killing the females would be counterproductive,

Male blue-lined octopuses inject females with venom to paralyse them before mating and avoid being eaten after sex.

Scientists have found that male blue-lined octopuses inject venom and paralyse females during sex to avoid being killed and cannibalised by their much larger partners. The male octopus of this species precisely injects a dose of its deadly tetrodotoxin venom into the females to immobilise them during copulation,