Symbiotic microbes are commonly found associated in higher organisms, and often have evolved to play an important role in host biology. Researchers have been studying the effects that microbial symbionts have on host physiology, their effects on host nutrition or protection against pathogenic microbial infections, but have recently begun to examine how they influence the brain and behaviour. Wolbachia pipientis, a gram-negative alpha-proteobacteria, intracellular bacterial symbiont infects approximately 40% of all insect species, including Drosophila. The fruit fly, Drosophila melanogaster, one of the most intensively studied organisms in biology and serves as a model system for the investigation of many developmental and cellular processes common to higher eukaryotes, and is naturally infected by several strains of Wolbachia. While Wolbachia are known to infect numerous host tissues, including the brain, little research has focused on how Wolbachia affects the nervous system and behaviour of its host, despite the impact behaviour has on host fitness.