Headwaters represent a substantial fraction of the Earth’s streams and rivers. Global climate change is expected to cause droughts of greater magnitude and frequency over the coming decades; the consequences of which are largely unknown for the organisation of headwater communities. Here, findings are presented from an experimental drought imposed on upland stream invertebrate communities in cascading, stream-fed mesocosms; believed to be the first study of its kind. A 99.95% reduction in flow over three months saw an initial exodus, followed by low drifting rates of macroinvertebrates. Drought reduced the quantity, but didn’t affect the taxonomic or functional quality of invertebrates known to be important salmonid prey items. Responses to drought are investigated according to the taxonomic and body size composition of these highly resolved invertebrate communities (studied for 40 years at The Llyn Brianne Observatory, UK), and discussed within the context of downstream energy budget constraints. A reinstated flow regime was followed by a swift return of communities representative of non-drought conditions. Relative to stable, lowland, lotic communities, the affinity of headwater communities for flashy flow regimes may prove advantageous in light of the expected intensification of the global hydrograph.