Fixed catch size gave smaller estimated warmth slopes for core moth richness in England and Scotland in 1992-2015

We tested whether monthly warmth slopes for recorded moth richness persisted at equal catch size. We used 685 trap-months from seven English and two Scottish ECN sites in two periods, 1992-2003 and 2004-2015. We kept core macro-moth taxon codes, single-night samples and months with at least ten valid samples and 100 individuals. Models controlled trap by calendar month, rain, sample count, mean sample date and linear time. Raw richness slopes were +2.19 to +4.83 taxa per C. Expected richness in a random sample of 100 individuals had slopes of +0.04 to +0.67 taxa per C. All four adjusted intervals for the fixed-size slopes included zero. Paired slope reductions were clear in England, but not in Scotland after four-test correction. Equal catch size changes the measured outcome. It cannot separate trap efficiency, adult activity and population size. Few Scottish sites, coarse weather, taxon exclusions and selected complete samples limit wider use. The package gives source hashes, sample and count tables, code, checks and a figure. We test no air pollution effect or causal climate-change effect.

moths · temperature · rarefaction · observation bias · richness · ECN · regional comparison