The ongoing climatic changes will have undisputable effects on biodiversity and ecosystems. For small ectotherms (e.g. insects) the current state-of-the-art focusses on physiological performances (often measured as critical thermal limits), warming tolerance (resilience) and phenotypic and evolutionary responses. These data provide input to models used to describe expansion – or more often restriction – of species distributions. The climate is changing especially rapidly in the Arctic. Much of the knowledge we have on responses (or lack hereof) to warmer temperatures in terrestrial arthropods is based on studies on temperate and tropic species. Further, the little we do know about the realized warming tolerance under field conditions in the Arctic is based on extreme physiological endpoints, such as critical thermal maxima, measured in the laboratory. The aim of the project is to investigate the consequences of increasing temperatures on behaviour and energy budget for coping with heat under field relevant conditions in Arctic insects. In doing so, the project will generate much needed information on potential overlooked consequences and resilience of Arctic insects to increasing temperature. Here, we want to explore to role of behavior for thermal adaptation and adaptive thermal responses, and assess the energetic consequences of increasing temperatures. The results might fundamental change our understanding of thermal adaptation in small ectotherms in general and the current predictions regarding the resilience to climate change specifically. Thus, there is a potential for reforming the research field.