Wolbachia is an intracellular endosymbiont present in most arthropod and filarial nematode species. Transmission between hosts is primarily vertical, taking place exclusively through the female germline, though horizontal transmission has also been documented. Several studies indicate that Wolbachia is capable of transfer between somatic and germline cells during nematode development and in adult flies. However, the mechanisms underlying horizontal cell-to-cell transfer remain largely unexplored. Here, we establish a tractable system for probing horizontal transfer of Wolbachia between Drosophila cells in culture using fluorescence in situ hybridization (FISH). First, we show that horizontal transfer is independent of cell-to-cell contact and can efficiently take place through the culture medium within hours. Further, we demonstrate that efficient transfer utilizes host cell phagocytic and clathrin/dynamin-dependent endocytic machinery. Lastly, we provide evidence that this process is conserved between species, showing that horizontal transfer from mosquito to Drosophila cells takes place in a similar fashion. Taken together, our results indicate that Wolbachia utilize host internalization machinery during infection, and this mechanism is conserved across insect species.Our work has broad implications for the control and treatment of tropical diseases. Wolbachia can confer resistance against a variety of human pathogens in mosquito vectors. Elucidating the mechanisms of horizontal transfer will be useful for efforts to more efficiently infect non-natural insect hosts with Wolbachia as a biological control agent. Further, as Wolbachia is essential for the survival of filarial nematodes, understanding horizontal transfer could provide new approaches to treat human infections by targeting Wolbachia Finally, this work provides a key first step toward the genetic manipulation of Wolbachia.