Leaf cutter bee brood cells. Close-up of the brood cells made by the leaf cutter bee, Megachile. These thimble-shaped structures were constructed by the adult bees from rose leaves as cradles for their young. The bee first constructs a tunnel in rotten material, in this case in the compost of a potted plant. It then cuts off pieces of leaves with its sharp mandibles and takes them back to its tunnel. When it has enough it weaves the leaves into a hollow container. The bee lays one egg into each container with a food pellet of gathered pollen before sealing them. The larva hatches and feeds inside the brood cell before pupating. Adult bees emerge the following year.