After the last young Eurasian Blue Tit left the nest I started checking the nestbox in the early morning and late evening. I was checking to see if any of the birds returned to use the nestbox as an overnight roost site.
This is what I saw 48 hours after the last youngster left. Those are Bird Fleas on the sides of the nestbox. I spent the rest of the day itchy, psychological as I never found a Flea or bite on me.