In many animals, Wolbachia is a reproductive parasite: an organism that manipulates the sex lives of its hosts to further its own ends. The hosts suffer. Some die, others become sterile, and even unaffected individuals must live in a skewed world with few potential mates. Wolbachia might seem like the archetypal ‘bad microbe’, but it has a beneficent side, too. It provides some unknown benefit to certain nematode worms, which cannot survive without it. It protects some flies and mosquitoes from viruses and other pathogens. The wasp Asobara tabida cannot make eggs without it.
