It may seem ridiculous that the parasites in [the David Cronenberg film] Shivers can spread themselves by making people have sex, but it’s no more ridiculous than what actual parasites do. The fungus that I discussed earlier, which infects flies and forces them to climb up grass in the evening, actually uses a second trick to spread itself as well. It makes the corpse of its host a sexual magnet. Something about the fly— something brought about by the fungus itself— makes it irresistible to uninfected male flies. They will try to mate with it, preferring it to living flies. As they grope the corpse they become covered with spores themselves. When they die, they themselves become irresistible. When will someone make their movie?

Carl Zimmer, Parasite Rex: Inside the Bizarre World of Nature’s Most Dangerous Creatures (2000)