In my apartment I closed up the ventilation in my bathroom with baking paper. The reason is since it is summer many insects like hornets, wasps and even centipedes started coming from that ventilation hole. Obviously I contacted my landlord. He told me to keep the hole closed, that no one before me had that problem and to keep my windows open when I showered so that there couldn't be a chance of mold appearing. He told me this over phone. Now I don't know if I should get a written statement from him because if mold gets in there, I don't want to pay for anything.
Information: I am from Germany, my landlord is actually a really cool guy but kinda greedy. I never had any other problems. I just don't know if he is too lazy or what I should do now.