Citizen science data reveals that earlier and shorter flight periods correlate with climate warming in the dark‐edged bee‐fly

•1. Understanding the impacts of climate change on insects is hindered by a lack of long‐term monitoring data for most species. Citizen science occurrence records provide opportunities to examine changes in the timing of life cycle events (phenology), even for relatively poorly sampled taxon groups. Here, we developed a workflow to examine the effects of climate change on insect phenology using occurrence records and tested it for the Dark‐edged Bee‐fly, Bombylius major Linnaeus 1758, in Britain.
•2. We used quantile regression to characterise changes in phenology as a continuous process between the start (emergence) and end (senescence) of annual flight periods from 1984 to 2024. Regression models were used to explore the sensitivities of the timing of emergence and senescence to explanatory climate variables based on hypothesised causal models.
•3. Between 1984 and 2024, emergence has advanced by about 9 days (at a rate of −0.23 d/yr. ± 0.04 d/yr) and senescence by about 22 days (−0.53 d/yr. ± 0.11 d/yr), with rates of change varying continuously between emergence and senescence. Consequently, the annual flight period has shortened by about 13 days (−0.33 d/yr. ± 0.01 d/yr) over the study period.
•4. Both advanced emergence and senescence correlate with climate warming, with maximum rather than average monthly temperatures more influential on phenological changes. Precipitation contributes to delayed senescence.
•5. Our workflow is generalisable to other insect species that lack long‐term monitoring, provided a minimum amount of occurrence records is available, and is adaptable to include trait analysis to understand variation in phenology trends among species.