The latitude change in NEON blacklegged nymph catches reversed when the early period changed from 2016–2018 to 2017–2019

Can changes in survey effort explain the latitude change in captured blacklegged tick nymphs at NEON sites? We used the open NEON archive dated 15 September 2026. We matched May–August surveys by site and month and separated changes in sampled length from changes in captures per meter. In 156 matched cells at 45 sites, the capture center changed northward by 0.736 degrees from 2016–2018 to 2021–2023. The exact effort and rate parts were −0.124 and +0.860 degrees. A planned check with 2017–2019 as the early period changed the direction: −0.333 degrees, with effort and rate parts of −0.147 and −0.186. The reversal remained on identical cells and with equal cell effort. Other quality, plot, method, and seasonal checks kept the first comparison northward. Thus, the chosen early period can change the direction even with equal sampled length in each cell. This is a finite-data audit of identified catches. It does not estimate a species range boundary or a climate effect. Irregular dates, capture probability, and unreported early enumeration subsampling can affect the rates. The package includes the unchanged source archive, provenance, a local plan, code, figures, and independent count checks. A full offline repeat gave identical hashes for 50 result files and figures.

species distributions · Ixodes scapularis · NEON · sampling effort · latitude center · biodiversity monitoring · baseline sensitivity · reproducible research