Bumble Bee Barrier

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.