In previous work, we identified muscle-specific stem cells, which asymmetrically divide to give rise to myoblasts, which fuse to form flight muscle fibres in Drosophila (Gunage et al., 2014). Here, we show the presence of lineal descendants of these stem cells as small, un-fused cells located superficially and in close proximity to mature adult muscle fibres. Normally quiescent, these cells become mitotically active following muscle injury. In view of their strikingly similar morphological and functional features, we consider these cells to be the Drosophila equivalent of vertebrate muscle satellite cells. Thus, in flies as in vertebrates, the stem cell lineage that generates adult-specific muscles is also available for myogenesis in mature muscle. The mechanism of satellite cell activation uses Delta in the muscle fibre signaling to Notch in satellite cells. These results demonstrate the mechanistic value of the fly for further studies on muscle regeneration.