I have not harvested my cocoons yet, but when I opened one for a photo op, I noticed the beginning of moisture condensing onto trays. My trays are stored outside and under cover to keep them dry. But under fall conditions, when moisture content in the air is high and temperatures go down, any water vapour in the air that is inside nesting tunnels condenses onto trays. This happens each fall, when there is lots of moisture in the air and temperatures start to drop. |Under these conditions, molds start growing onto the surfaces of cocoons. |These molds do not harm the bees that are inside each cocoon, but moldy cocoons are a little more messy to clean.
For easier harvesting and cleaning, harvest cocoons before we get too far into the wet fall, this mold growth can be prevented. If you find mold present wash cocoons in a 0.5% bleach bath.
In other words, harvest your cocoons as soon as you can.