Hi! @seltmann shared a "famous" bee trait: [intertegular_span_Apoidea] (https://www.researchgate.net/publication/256458920_Estimation_of_bee_size_using_intertegular_span_Apoidea) a proxy for dry weight or body size. classification could be something like: volume ~ dry weight ~ intertegular span trait is defined in the Cane 1987 paper: Cane, James H. "Estimation of bee size using intertegular span (Apoidea)." Journal of the Kansas Entomological Society (1987): 145-147. https://www.researchgate.net/publication/256458920_Estimation_of_bee_size_using_intertegular_span_Apoidea @seltmann is working on a literature list for this trait at https://www.zotero.org/groups/4605590/bee_morphology_functional_and_life_history_traits/library @Daniel-Mietchen please let me know if you need more information.