Altica sylvia Malloch, 1919 and Mantura chrysanthemi (Koch, 1803) co-inhabit natural and commercial stands of lowbush blueberry, Vaccinium angustifolium Aiton (Ericaceae), in eastern Canada and the northeastern United States. Whereas A. sylvia feeds on lowbush blueberry plants, an important crop to the region, M. chrysanthemi feeds on sheep sorrel, Rumex acetosella L. (Polygonaceae), an important weed frequently found in lowbush blueberry fields. This study provides a detailed morphological examination of males and females of these flea beetles to compare species and sex-specific features. Scanning electron microscopy identified key distinguishing features, including internal and external sexual dimorphism of both species.