The blue willow beetle (Phratora vulgatissima), formerly Phyllodecta vulgatissima, is a herbivourous beetle of the family Chrysomelidae. It is black with metallic shine in nuances individually varying from a more common blue to a rarer bronze. It is distinguished from P. vitellinae by the latter more commonly displaying bronze nuances. The larvae undergo three instar stages from hatching to pupation.