To check if the silk was lethal to bacteria, Piorkowski’s team placed threads from three tropical spider species — giant golden orb weaver (Nephila pilipes), lawn wolf spider(Hippasa holmerae) anddome tent spider (Cyrtophora moluccensis) — in petri dishes and grew four types of bacteria, including E. coli, in perpendicular lines across the silk. Wetting the silk threads with an assortment of nutrient solutions showed that the bacteria readily grew on all three types of spider silk when extra nitrogen was available. Randy Lewis, a spider silk biologist at Utah State University in Logan, cautions against ruling out antibacterial features in all spider silks, though.