The mechanisms underlying adult stem cell behaviour are likely to be diverse and have not yet been investigated systematically. Here we conducted an unbiased genetic screen using Drosophila ovarian follicle stem cells to probe essential functions regulating self-renewal of epithelial stem cells. Surprisingly, we find that niche adhesion emerges as the most commonly affected essential stem cell property, and that proliferation is critical for stem cell maintenance. We also find that PI3K pathway activation enhances follicle stem cell function, whereas mitochondrial dysfunction and reactive oxygen species production lead to stem cell loss. Moreover, we find that most genes required specifically in the stem cell of the follicle stem cell lineage are widely expressed but are not required for the maintenance of ovarian germline stem cells. These findings highlight the fundamental characteristics of follicle stem cells as an important stem cell paradigm that contrasts with some other stem cell models, where repression of differentiation or relative quiescence is crucial.