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.

A nesting tray with 6 routered channels containing mason bee cocoons, and cotton type fluff in two of the channels.

Here I have lifted some of the fluff out to show how it neatly fits into the channel.

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.

For comparison, this appears like a spider web,  which either contains young spiders or an adult spider.

 When I find resin bees inside nesting tunnels, I remove any mason bee cocoons , remove mason bee debris out of tunnels with a tooth brush, close up the nest and set out side ready for next year.

Two delicately placed resin walls.  No bees were in these cells.

Resin bee pupae within compartments made of resin.

Last year’s resin bees emerged during summer months when resin softened up with the heat.

Last week a mason bee keeper asked me to look at these two photos and give them feedback on the insects inside the nesting tunnels.  Every nesting tunnel tells a story!

These are beneficial wasp pupae encased in a very delicate cover.   These beneficial wasps provision their nests with either spiders,  aphids or moth larvae.  Sometimes if an egg does not  develop the larvae food remains in the cell.

This is a picture of cocoons harvested from nesting tunnels. The dark brown, still with mud attached, is from the early  spring mason bee Osmia lignaria.  The reddish cocoon with its bright  orange fecal material and masticated leaf plugs are probably  Osmia californica.  Osmia californica is active towards the end of the  early spring mason bee activity.