Spreading at 12% a year across 17 Western state, this invasive species -- with its high silica content and spiky heads and seeds that cut animals' mouths -- forces livestock to go elsewhere to feed. That can raise costs for ranchers and result in skinnier cattle.
A fungus is quickly wiping out most of North America's bats. Bats eat vast quantities of bugs that would otherwise eat crops, so if researchers can't save them, U.S. agriculture will suffer.
Oil from the broken well has befouled beaches and wetlands in Louisiana, Florida and Alabama over the last two months, killing wildlife and dampening the normally vibrant tourism industry.