In the outer walls of our house are some holes in the clinker (missed out mortar). Probably for ventilation.
Some of these holes are regularly visited by bumblebees. Basically, this is not a problem - but near the terrace it is unwanted.
BTW: I will install the barriers at the earliest in September - from then on, no [living] bumblebees should fly around.
UPDATE 05.07.2018: added a less break-sensitive V2. It fits on ventilation holes with the dimension of 8x50mm up to 15x70mm.
I printed mine with PLA+.