aemeijers wrote:

Mice and bugs and spiders and such, will happily nest in overhead
fiberglass. It easily supports their trivial weight. As long as they
have a non-slippery path up there, they will move right in. I found wads
of fiberglas in the drawers of this desk, where the mice carried it on
their way upstairs since they were passing through the crawlspace.

That's been my experience as well. One year old house, crawlspace, fiberglass
between the trusses. Pulled the fiberglass down to spray some foam insulation
under a tile floor bathroom and found lots of mouse turds in the glass.