"And thanks, we'll eat the plate, too..."
Likely "preaching to the converted" but long known are the habits of a strong
hygenic colony in removing _any_ detritus found within the hive body.
It is not unusual to find wild colonies with absolutely no "rubbish" present
where the lower extent is part of the entrance structure, even when said
entrance is large enough to allow birds/lizards/frogs/bugs entry with obvious
sign within the hive body the bees have made their own space, chewing at
surrounds.
What is interesting about the reactive in that pix is that they are into a plastic
coated object - I would have thought not and used a plaatic coated plate for
that very reason.
As our Carolinian friend has commented, the leavings should now be dust on
the bottom board or invisible within the immediate surronds of the entrance...
... assuming you know better than to be using SBBs
Cheers.
Bill