Leafcutter bees cut circular holes from leaves (especially rose leaves and other plants in the rose family), and create a cigar shaped nest case. Here you can see the bee carrying a piece of cut leaf, constructing the nest, and the final product, with several cases together. Notice that the cases are sealed with a perfect circle! The nests are constructed in bee boxes, or as here, under rocks. The bees lay their eggs in these cases and provision them with pollen balls.