Q: I was changing a vent fan in a bathroom when I found this is the ceiling. Do you have any idea what type insect this is?
A: Let’s use logic and the process of elimination:
Only three insects build paper nests like this.
1. Yellowjackets nest in the ground, very rarely in walls or attics.
2. Bald-faced hornets make their home in football-shaped gray paper nests in trees and under eaves. Also, rarely in walls or attics.
3. European hornets commonly make nests in wall voids or attics.
Therefore, I believe this is a European hornet nest. QED
Nests of all three insects are only used one year. They are abandoned every fall. Since this one is so large, my guess is that it was built some year previously.
You can remove it or leave it where it is: your choice.