<p>Aerial robots, capable of autonomous flight and task execution, are increasingly applied in photography, geo-mapping, surveillance, agriculture and logistics fields. As these technologies evolve, the need for robust, reliable and self-sustaining aerial robots (SSARs) with extended endurance and range becomes more urgent. Integrating energy-harvesting technologies in aerial robots is essential to enable self-sufficiency by using environmental energy sources. The analysis of the design principles of aerial robots and the exploration of energy utilization models from nature that offer symbiotic energy design concepts are essential for creating compact, versatile and efficient SSARs. Here, we discuss the emerging paradigm of environmental energy-harvesting and storage technologies and construct system-level energy matching and analyse flight energy-saving technologies guided by symbiotic energy principles, such as self-sensing, advanced drives, dynamic soaring and swarm intelligence. We also address technical challenges in the evaluation, design and development processes and discuss future directions considering interdisciplinary research in artificial intelligence and advanced materials. Central to this Review is an emphasis on a symbiotic energy design paradigm that integrates bionics, multifunctionality and integration in developing SSARs.</p>