May-minus-June warmth gave no clear repeated link to Meadow Brown flight dates in England and Wales, 1985-2024

We tested whether the order of monthly warmth predicts Meadow Brown mean flight dates at a fixed May-June mean. We used 20,959 site-years at 1,320 public UKBMS sites in England and Wales in 1985-2004 and 2005-2024. Four site-intercept models controlled time and August-September weather. Slopes for a 1 C warmer May and 1 C cooler June were +1.06, +3.43, +0.58 and +4.77 days. Only later Wales had a four-test adjusted interval above zero. All intervals included zero with year effects. Removing late-season controls kept all estimates positive, but early Wales changed sign after one year omission. The evidence does not establish a repeated nonzero link. Coarse weather, only 20 years per model, shared regional weather, selected sites and missing visit records limit inference. These are associations, not causal effects or climate-change attribution. The package includes code, source hashes, a figure, aggregate model moments and numerical checks. External record data stay outside the publication.

phenology · butterflies · temperature order · Meadow Brown · observation bias · regional replication · null result