Spiders, it turns out, are even deadlier than we previously believed. Not only can they bite, but they help construct accurate guns.
When making certain things, like weapons and scientific instruments, accuracy is of the essence. A lot of engineering went into making weapons that shot straight, and microscopes that could be adjusted minutely, but that was no use if a person couldn't aim them correctly. This is why nearly all old weapons, and many old scientific instruments, have bits of spider in them. Specifically, the bits of the spider that come out of the back side.
A spider's silk is less than one ten thousandth of an inch wide, much finer than the width of a human hair, and although it only lasts about a week in the wild, it will hold up indefinitely when encased in glass or plastic. Webs were the only way to make anything with a "sight" or a "scope" in the name. The silk was fine enough to make accurate cross-hairs on the sight. In the UK, they used the local Epeira diademata. The English weapons manufacturers would simply send out their apprentices to find two hundred local spiders every August and harvest enough silk for the year before releasing them back into the wild. They spider would be put onto one prong of what looked like tweezers. Someone (probably another long-suffering apprentice) blew on the spider to make it feel threatened, and it hopped off the tweezers, making a drag line which was wound around the two prongs.
When World War II broke out, the United States also needed the silk, and supply started dwindling. A whole crop of amateur spider wranglers sprung up, including a woman named Nan Songer, who went from a simple interest in creepy crawlies to producing so much silk that the US appealed to Mexico to send her more spiders for the war effort (they obliged). The American spider-wrangler method was to fasten the spiders to a kind of harness or stocks - Songer made the stocks out of Yucca and used hair pins on either side of the spiders to fasten them in place - and then tickle their nerve centers until they produced the right kind of silk. The silk was wound around a steel frame to dry and then sent off. Songer, and most wranglers like her, actually preferred to use the black widow spider, both for the silk it produced and because it was slower than less deadly spiders.
Although demand slowed after the war ended, it wasn't until the 1960s that etching on the sights with electricity was more practical than harvesting spider silk. It's said, in fact, that some military bases still have spiders on hand in case anyone needs to repair old equipment, even if that equipment is just kept around for show. I don't envy the poor soldier who has to milk the spiders now.