Male blue-lined octopuses inject females with venom during mating to paralyze them and avoid being eaten. This venom, tetrodotoxin, is typically used by animals for defense or hunting. Research by Wen-Sung Chung and his team at the University of Queensland discovered this unique mating behavior. The venom causes the female to become immobile but does not kill her. This evolutionary adaptation ensures successful mating and prevents cannibalism by the larger female. Males have larger venom glands to produce more venom and overcome the female’s resistance. This co-evolutionary arms race between males and females showcases nature’s fascinating tactics for survival.
https://www.newscientist.com/article/2471120-male-octopus-injects-female-with-venom-during-sex-to-avoid-being-eaten/