Wolbachia pipientis is a symbiotic bacterium that lives within the cells of filarial nematodes and about 40 percent of the world’s arthropods, including insects, spiders, mites, and crustaceans. It passes from mother to offspring and, in arthropods, is generally associated with host reproductive manipulations such as male killing, feminization, parthenogenesis, and cytoplasmic incompatibility (CI). In research labs, Wolbachia is a model organism to study animal-microbe interactions, evolution, genetics, ecology, and human health.