An illustrated and updated key for European Spilomyia species is presented. French and Swiss distribution data for Spilomyia species are brought together, and discussed. We argue that the available records do not provide an adequate basis for assessing the conservation status of saproxylics like Spilomyia species, because an unknown proportion of them are derived from unsustainable populations, dependent on old trees isolated from forest, or in forests of young trees, where continuity of the larval microhabitats provided by the few old trees present is not sustainable. This lack of site quality data means that unsustainable populations of these syrphids cannot be recognised as such, leading to under-estimation of the degree of threat to which the species are subject.