Everyone knows spider silk is really strong, but scientists want to make it even stronger. In just such an effort, researchers sprayed 15 spiders from the Pholcidae family with graphene or carbon nanotubes and discovered that the arachnids can add the tough artificial particles into their silk. The resulting hybrid fiber is 3.5 times tougher than the strongest ordinary silk, New Scientist reports. Researchers don’t know details of how the spiders are incorporating the carbon structures into the silk; they could be added to the outside of the thread, or the spiders could be absorbing the particles from the environment and using them in the silk’s formation. Four spiders also died after being sprayed, indicating that nanoparticle sprays are likely hazardous to arachnids.