I recently observed a leafcutter bee utilizing American chestnut leaves for nesting materials. The bees are solitary in nature (no hives like a honey bee) and will cut small portions of suitable leaves to be carried back to the nesting cavity - usually a hollow plant stem or abandoned exit hole from a boring insect in a tree - and placed just so to construct chambers. Within these chambers, the bee collects and deposits a ball of pollen. Upon this pollen, an egg is laid and then the chamber is sealed up with another leaf cutting. Onto building the next one!
A leafcutter bee can be seen towards the left carrying a newly cut piece
of American chestnut leaf.