There have been half a dozen reports of cotton fluff inside the nesting tunnels. Here is one I found myself. Most of the fluff is just that, but two cocoon type structures were found in the center row. If someone knows what this is please let us know.
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| A nesting tray with 6 routered channels containing mason bee cocoons, and cotton type fluff in two of the channels. |
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| Here I have lifted some of the fluff out to show how it neatly fits into the channel. |
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| Two cocoons were found inside this fluffy material. You can see the end cap directly above where the cocoon is held in the photo. The end cap is made of several layers of mud and is thicker than the usual mason bee end cap. |
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| For comparison, this appears like a spider web, which either contains young spiders or an adult spider. |
I was just looking inside my Orchard Mason Bee house and found a good wad of the same cottony material. Cocoons were inside as well.
I wasn't sure if these were also OMB's or a parasite of some kind. I'd love to know if anyone answers your question.
European wool carder bee (Anthidium manicatum)? We have a row of this fluffy stuff in our Mason Bee viewing box – not in one of the tunnels, but between the side of the nesting tray and the inside edge of the box.