The gypsy moth (Porthetria dispar) lays its eggs on the leaves of oaks, birches, maples, and other hardwood trees. When the yellow hairy caterpillars hatch from the eggs, they devour the leaves in such quantities that the tree becomes temporarily defoliated. Some trees can withstand two years of such defoliation, but other trees often die in the infestation year. In 1869, Professor Leopold Trouvelot (1827–1895) originally brought gypsy moth egg masses from France to Medford, Massachusetts. His intention was to breed the gypsy moth with the silkworm to overcome a wilt disease of the silkworm. He placed the egg masses on a window ledge, and evidently the wind blew them away. Only a decade later, the caterpillars covered trees in that vicinity, and in twenty years trees in eastern Massachusetts were being defoliated. Since that time, it has spread (in cycles) to at least twenty-five states in the United States.