Fig. 1: Phenology of Odonata in relation to seasonal environmental conditions.

a, b Phenological fundamental tracking regulates species´ life cycles by synchronising them to optimal seasonal moments. a Fitness increases when the timing of phenological events aligns to the timing of ideal environmental conditions. b Phenological responses are triggered by environmental cues, such as certain photoperiod threshold (blue line), or combined photoperiod and temperature thresholds (brown line). These environmental cues link to—unknown—underlying drivers of optimal timing (a and b adapted from¹¹). c Example of the life cycle of the dragonfly Sympetrum striolatum which is regulated by seasonal environmental conditions. Arrows note phenological events triggered by environmental cues. Eggs are oviposited in October when cold temperatures induce a diapause in their embryonic development that lasts until spring, when development resumes triggered by photoperiod and temperature cues⁷⁴. Larvae hatch and develop for two to four months, depending on water temperature. Last instar larvae emerge, again triggered by photoperiod and temperature cues. Adult complete maturation and reproduce⁷⁴. Alternatively, if oviposition occurs earlier, eggs can develop without diapause and larvae hatch in autumn to enter a diapause that lasts until spring, when development resumes⁷⁴. Other temperate odonates have different life cycles varying in length from less than a year to several years⁷⁴, most of which are regulated by phenological fundamental tracking. d 5th and 95th percentile of dragonfly and damselfly flight periods in Great Britain, together with variation in radiation (orange) and temperature (blue) across the season (upper panel), indicated as standard deviation from the cross-year average (grey dashed line). Coenagrion scitulum is not shown because its rarity in the study system does not allow to derive a representative flight period. Artwork in (c) by Zijing Deng.