Spring rain gave no clear warmth interaction for a butterfly flight-date gap in England and Wales in 1985-2024

We tested whether March-April rain changed the warmth slope of the Large Skipper minus Orange-tip mean flight-date gap. Four site-effect models used 3,225 matched site-years in England and Wales in 1985-2004 and 2005-2024. Each calendar year had equal total weight. Models controlled winter temperature, later spring temperature and time. Warmth and rain product estimates were -1.79, +3.43, -3.91 and -2.48 days per C per 100 mm in England early, England late, Wales early and Wales late order. All four adjusted 95 percent intervals include zero. All estimable sensitivity intervals also include zero. The Welsh samples had only two and nine sites. These data do not establish a common interaction or its absence. Missing visits, selected populations, early-season limits, country weather and few annual exposures limit inference. The package gives code, source hashes, aggregate results, a figure and independent numerical checks. External source data and record-level outputs remain outside the bundle.

phenology · butterflies · rainfall · temperature interaction · observation bias · matched species · null result · regional replication