Asian longhorn beetles were transported from China to the United States in infested packing material and are a tree pest. The emerald ash borer has killed 20 million ash trees in Michigan, Ohio and Indiana, and firewood quarantines aim to prevent new infestations. Gypsy moths, which spread to the US in 1870, have larvae that defoliate oak and aspen trees, though small mammals and birds prey on the moths. Western pine beetles infest ponderosa and Coulter pine trees in western states and their tree loss is considered a normal ecological process.