The Germans fought in a number of mosquito infested areas. As a result they developed nesstin to cover beds as well as wearable nets for the head. They even had a small dome tent looking shelter made of netting. Mosquitos are a known carrier of illness including Malaria. Mosquitos have been a known carrier of this disease since the 1880s. Netting provides a physical barrier between the mosquito and its intended victim. The Soviet army applied juniper oil to over bed mosquito nets to repel to repel these pests during their WW2 campaigns in Central Asia. I am not certain if the German army was doing something similar.