Scientists have uncovered a 400-million-year-old genetic secret that gave spiders the ability to produce silk and weave their webs. Spiders didn't begin their journey on Earth in the same way as they are known today. Arthropods such as our eight-legged weaver owe much of their evolutionary success to the slow, repeated modification of appendages. One of the crucial changes that allowed spiders to survive and diversify into more than 53,000 species was the spinnerets, a silk-spinning organ found on the underside of a spider's abdomen.