One of the fundamental challenges of conservation biology is gathering data on species distribution and abundance. And unless conservationists know where a species is found and in which numbers, it is very difficult to apply effective conservation efforts. In today's age of increasingly powerful monitoring tools, instant communication and online databases, one might be forgiven for thinking that such knowledge is easy to come by. However, of the approximately 5,400 terrestrial mammals on the IUCN Red List, no fewer than 789 (ca. 14%) are listed as 'Data Deficient' (IUCN 2012) – IUCN’s term for 'haven't got a clue'. Until recently, the only way to gather information of numbers and distribution of terrestrial mammals (and many other vertebrates) was through observational-based approaches such as visual records, the presence of tracks or spoor or even identification from bushmeat or hunters' trophies pinned to the walls in local villages. While recent technological developments have considerably improved the efficacy of such approaches, for example, using remote-sensing devices such as audio- or camera-traps or even remote drones (Koh & Wich 2012), there has been a growing realization of the power of molecular methods that identify mammals based on trace evidence. Suitable substrates include the obvious, such as faecal and hair samples (e.g. Vigilant et al. 2009), to the less obvious, including environmental DNA extracted from sediments, soil or water samples (e.g. Taberlet et al. 2012), and as recently demonstrated, the dietary content of blood-sucking invertebrates (Gariepy et al. 2012; Schnell et al. 2012). In this issue of Molecular Ecology, Calvignac-Spencer et al. (2013) present a potentially powerful development in this regard; diet analysis of carrion flies. With their near global distribution, and as most field biologists know, irritatingly high frequency in most terrestrial areas of conservation concern (which directly translates into ease of sampling them), the authors present extremely encouraging results that indicate how carnivorous flies may soon represent a strong weapon in the conservation arsenal.