An intracellular microorganism found in D. fuscipennis exhibits the basic morphology characteristic of rickettsiae. It is regularly present in the gonads and abdominal ganglia, less frequently in other tissues. The rickettsia has no overt cytopathic effect in host cells, does not noticeably affect the fitness of the host, and is likely transmitted transovarially. On the basis of arthropod association, morphology, and relationship to the host cell the rickettsia resembles members of the genus Wolbachia. Its relationship with the host and the significance of a host-provided membrane enclosing each rickettsia are discussed.