I hate pushing thumbtacks in my hives for the off-the-shelf mouse guards, so I thought to give it a try designing something that can simply be shoved in the existing entrance and clicks itself in place.
Surely it would be convenient for the beekeeping thingiverse community if it was customizable, because hive entrances might differ.
This is a new design, so it isn't thoroughly tested; don't know how it holds over a winter.The plastic should be ok (use PETG), but the bees might cement it in place with propolis, so removal in spring might be slightly harder than installation in fall.
The pictures show use for different hives, also what sort of entrance it is intended for (height 6-8mm). The guard is designed to mimic the original entrance shape, to avoid unnecessary disorientation from the workers. Not sure if red it the appropriate color though.