Answer: Rifle Scopes
Long before we had the technology to make flexible and durable material for the sight mechanism inside rifle scopes and sensitive scientific instruments, mother nature did. For most of the 20th century, the crosshairs of rifle scopes (as well as bomb scopes in planes, periscopes in submarines, and many different kinds of scientific devices) were made from spider silk.
Why spider silk? It’s extremely thin (thousands of times thinner than a human hair) but extremely strong (spider silk draglines are capable of withstanding the same tension as steel alloys, but at a smaller diameter) and it’s resistant to shock (a rather critical trait for a scope attached to a rifle).
The peak of spider silk production for optics was during World War II where specialized handlers in the United States harvested tens of thousands of spiders’ silk for the War Department. One particular harvester even became famous for her wartime efforts. Nan Songer, a California native, was an amateur entomologist that made a name for herself as quite a bug expert. When the war broke out, the government asked her if she could produce large quantities of spider silk and she turned a room in her home into a full-on spider-silk production facility—the photo here is from a 1944 issue of Popular Science featuring a write-up about her operation.
Throughout the war and for some years afterward, Songer was the primary source of spider silk, largely from female Golden Garden, Green Lynx, and Black Widow spiders, in both military and civilian applications.