Cerambyx cerdo and C. welensii in Europe: threatened insects or insect pests?

Cerambyx cerdo and Cerambyx welensii are large wood-boring beetles associated with living oak trees. They exhibit partially overlapping distributions and similar behaviors but differ significantly in their conservation status. C. cerdo is classified as ‘Vulnerable’ on the IUCN Red List of Threatened Species and requires strict protection, while C. welensii is an emerging pest in several countries, posing a growing threat to oak trees. Interestingly, the conservation status of C. cerdo appears to vary regionally, particularly in southern Europe, where the species is sometimes regarded as a pest in urban areas, causing significant damage to trees and posing potential risks to public safety. This issue was highlighted in Central Italy through two separate visual surveys, complemented by trap catches. Notably, C. cerdo was found to be responsible for damaging Quercus robur in a street alignment, while C. welensii was observed affecting Q. ilex in urban parks. In addition, an analysis of citizen science data from the iNaturalist platform between 2020 and 2024 revealed significant differences in the distribution of both species. The number of records for C. welensii in Europe was surprisingly lower than C. cerdo. While C. cerdo was frequently recorded across multiple countries, C. welensii accounted for only about a quarter of the records of C. cerdo, even when only southern areas are considered. These findings highlight the need for more comprehensive studies to gain a deeper understanding of the true distribution, ecological impacts, and conservation status of both C. cerdo and C. welensii. Additionally, citizen science data collection is suggested as a valuable tool for monitoring these species and potentially helping to ensure that conservation measures are based on accurate and up-to-date information.