I’m not sure how many people still read this but it’s worth a try.
Has anybody got any previously occupied nestboxes? If so, could you scrape the nest contents into a sealed freezer/sandwich bag with the following on the label:
Grid reference, date collected, host species (what nested in the box).
Also, if anybody notices fleas on their family pets, a selection of them into a container with the same data would be most welcome.
Let me know and I will collect.