What are the black spots on my cocoons?

During mason bee cocoon harvest, many people ask about the little brown or black flecks that are found throughout their nesting materials. Don’t worry, these are not a sign of disease or pests. As the mason bee larvae eat the pollen loaves they produce waste, this is also known as mason bee frass. When the larvae spin their cocoons they push the frass outside of the cocoon. It may break into small pieces, or remain unbroken in long loops!  The frass can take a little friction to remove any stuck to the cocoon during washing.