Reclaiming the Unwanted: Mining Scientific Gold from multi-trap bycatch

Entomology-based research projects often involve setting up mass-collecting traps to obtain large-scale data on species or communities. Many of these projects gather not only the target taxa but also a large amount of bycatch, which often remains untouched or is even disposed of once the project has ended. Here, we have examined bycatch that has been collected in a project to promote biodiversity in the forests of the Swiss Pre-Alps. Multiple traps were set up in three forest reserves near deadwood, to monitor xylobiontic beetles as bioindicators between 2015–2018. The resulting bycatch was analysed about eight years later. Specimens were sorted, prepared, and in most cases identified to species level. From the 1,105 analysed bycatch individuals, we focused on 254 species, representing the groups Arachnida (Araneae, Opiliones) and Hymenoptera (Anthophila, Chrysididae, Eumeninae, Ichneumonidae, Pompilidae, and Sphecidae sensu lato ). Most samples were recorded in flight interception traps near herb layers and in the tree canopy. Remarkably, we recorded two rare ichneumonid species, Casinaria dubia Tschek, 1871 as a first record for Switzerland and Bioblapsis polita (Vollenhoven, 1878) as a first record for Switzerland since 1958. Furthermore, we found the rare European spider Episinus maculipes Cavanna, 1876, representing a first record for eastern Switzerland. Our study highlights the importance of well curated bycatch samples, even beyond the duration of the project. Future utilization of such samples may provide precious insights into the ecology and distribution of rare taxa.