Possible factors influencing size variability in morphology of adult Cyclotrachelus sodalis (Coleoptera: Carabidae)

Cyclotrachelus sodalis (LeConte) is one of the most common species of ground beetles in Northeast Iowa, and it is likely to be an important bio-control agent.  During ongoing Northeast Iowa surveys looking at ground beetle communities, we found two distinct size morphs of C. sodalis.  There is a significant difference between large and small morphs in both males and females.  The two morphs were confirmed to be the same species.  In evaluating what may cause this difference in the size morphs of C. sodalis, we found no significant difference in size between what appears to be two distinct generations per summer, one in late June and another in early August.  There also appears to be no relationship between the size of C. sodalis and habitat type.  Both large and small morphs are present in a variety of habitats including native and restored tallgrass prairies, roadsides, and agricultural fields.  Other potential factors that may influence the size of C. sodalis to be considered include diet and temperature during development.