We ran 10 Malaise traps along a latitudinal gradient in five old-growth forests: San Felasco Hammock, FL (30° N, 82° W); Tall Timbers Research Station, FL (31° N, 84° W); Hitchiti Experimental Forest, GA (33° N, 84° W); Patuxent Wildlife Research Center, MD (39° N, 77° W), and Shaw Woods, Ontario (46° N, 77° W). Of 18,791 ichneumonid wasps collected, 1,487 campoplegines and 4,494 ichneumonines were sorted to 241 species (95 species of Campopleginae and 146 of Ichneumoninae). Campoplegine species richness was highest at the Georgia site: San Felasco (20 species), Tall Timbers (32), Hitchiti (49), Patuxent (35), and Shaw Woods (12). Ichneumonine species richness was highest at the Maryland site: San Felasco (47), Tall Timbers (30), Hitchiti (44), Patuxent (68), and Shaw Woods (37). The results confirm reported trends that peak North American ichneumonid species richness lies at midlatitudes. However, they document greater biodiversity in the southern states and a broader peak than previously reported.