Phenology, the seasonal timing of life events, is an essential component of diversity patterns. However, the mechanisms involved are complex and understudied. Body colour may be an important factor, because dark-bodied species absorb more solar radiation, which is predicted by the Thermal Melanism Hypothesis to enable them to thermoregulate successfully in cooler temperatures. Here we show that colour lightness of dragonfly assemblages varies in response to seasonal changes in solar radiation, with darker early- and late-season assemblages and lighter mid-season assemblages. This finding suggests a link between colour-based thermoregulation and insect phenology. We also show that the phenological pattern of dragonfly colour lightness advanced over the last decades. We suggest that changing seasonal temperature patterns due to global warming together with the static nature of solar radiation may drive dragonfly flight periods to suboptimal seasonal conditions. Our findings open a research avenue for a more mechanistic understanding of phenology and spatio-phenological impacts of climate warming on insects.

物候学，即生命事件的季节性时间，是多样性模式的重要组成部分。然而，所涉及的机制很复杂且尚未得到充分研究。体色可能是一个重要因素，因为深色体质的物种吸收更多的太阳辐射，根据热黑化假说的预测，这使得它们能够在较低的温度下成功地进行体温调节。在这里，我们表明蜻蜓组合的颜色亮度随着太阳辐射的季节变化而变化，早季和晚季组合较暗，中季组合较亮。这一发现表明基于颜色的温度调节与昆虫物候学之间存在联系。我们还表明，蜻蜓颜色亮度的物候模式在过去几十年中取得了进步。我们认为，由于全球变暖以及太阳辐射的静态性质而导致的季节性温度模式的变化可能会导致蜻蜓的飞行期达到次优的季节性条件。我们的研究结果为更机械地理解气候变暖对昆虫的物候和时空物候影响开辟了一条研究途径。