Report on the largest known occurrence of morphological anomalies in ground beetles (Coleoptera: Carabidae)

We report on one of the largest known occurrence of minor morphological anomalies in adult ground beetles (Coleoptera: Carabidae) in North America. Carabid beetles were caught in pitfall traps in 2006 in ash (Fraxinus spp.)-dominated stands in southeastern Michigan. About 10% and 32% of the trapped individuals and species, respectively, showed morphological anomalies that ranged widely from the presence of tumors, cysts, fossae, misplaced setae, and missing and fused elytral striae to incomplete pronotum. The genus Pterostichus Bonelli had the greatest numbers of anomalies that were present primarily on the elytra, although the head, pronotum, and abdominal sternites were also affected. Within species, Pterostichus melanarius (Illiger), the introduced European carabid beetle, had the greatest numbers of morphological anomalies. Slightly more females than males with anomalies were caught in these forest stands. The occurrence of such high numbers of morphological anomalies in adult beetles across the central hardwood forests is perplexing, and we suggest future studies focus on elucidating its causes within this forested landscape.