If you maintain a box for bats, you'll need to occasionally look inside to make sure wasps have not built a nest inside it. Bats may be reluctant to occupy a bat box or a box chamber that has an active wasp nest. The nests take up space inside the box, and bats could be killed by the stings of an aggressive wasp species.
While cleaning a bat box is best done in the winter when both bats and wasps are gone, I procrastinated and just cleaned my bat box the other day. It has had a number of wasp nests in it, some for a couple years. I've been lucky enough to have had bats in the box for the last 3 summers and they have co-existed with the non-aggressive paper wasps within.
It is still early enough in spring that bats have not yet returned and the wasps are not active. If bats were back and the wasp nest active, I would only attempt a cleaning after dark, when the bats have departed for the night and the wasps are not as active. Even then, I'd proceed cautiously.
I used 2 pole sections from my roof rake that allowed me to reach all the way up to the top of the box without difficulty. I was able to detach all the nests - about 4 nests of various sizes came out.
This is the only way recommended to remove existing wasp nests. NEVER use wasp or insect spray inside a bat box!
The box is now ready for the bats' return and I will try to make sure I clean it out yearly. Hopefully I've cleared the way for a few more bats to occupy my box!
Read more about Bat Houses and Wasps on the Bat Conservation International website.