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Ball-roller dung beetles of the subfamily Scarabaeinae exhibit two nesting patterns ranging from simple nests (nesting pattern IV) to highly complex nests with parental care (nesting pattern V). Most species of the genus Canthon build a simple nest formed by a single brood ball that is abandoned after oviposition. We studied the nesting behaviour and brood ball architecture of two dung beetle species from South America. Canthon unicolor (Blanchard, 1846) and C. histrio (Le Peletier de Saint-Fargeau & Audinet-and Serville, 1828) construct a shallow nest containing a single brood ball. This brood ball is unique in that it is covered with a thick shield layer made of soil. The shield layer provides to the final brood ball an amorphous external aspect, never described in roller dung beetles. It is less dense than the brood ball layer, and provides, an additional post-ovipositional care. Our results suggest that the nesting behaviour observed in C. unicolor and C. histrio can be considered a new variation of the nesting pattern IV in dung beetles, in which post-ovipositional care through the outer shield layer could increase survival chance of the offspring by protecting them from potential predators, desiccation and a variety of other environmental hazards. [ABSTRACT FROM AUTHOR]