Taxonomic and methodological biases in saproxylic beetles: Body size, trophic group and detection probability

Smaller insect species are routinely described later than larger species, perpetuating the Linnean shortfall. Using 425 saproxylic beetle species from 28 veteran oak sites, we test whether body size varied with year of description and earliest georeferenced record year, and whether body length predicted detection probability. Linear models show a significant negative relationship between body length and both year of description ( β = −0.00063 ± 0.00021 SE, p = 0.003) and earliest georeferenced year ( β = −0.00057 ± 0.00024 SE, p = 0.016). Single‐season occupancy models reveal only a marginal size effect on detection ( β = −0.021, p = 0.055); instead, the trophic group drives variation, with sapro‐xylophagous species detected most readily. Fourteen species remain undescribed, and 29% lack any georeferenced record, highlighting combined Linnean and Wallacean shortfalls. Historical taxonomic bias towards conspicuous species and methodological undersampling of specific trophic guilds together impede accurate biodiversity assessment. We recommend integrated taxonomic revision, diversified trapping protocols and trait‐based occupancy models to rectify these biases and improve conservation planning.