A mysterious fungus is threatening to wipe out some isolated populations of rare rattlesnakes.
In Illinois, the fungus infects about 15 percent of eastern massasauga rattlesnakes: it kills up to 90 percent of those that contract it. There are only about 300 of the snakes in Illinois, mostly in Clinton county. The swamp rattler has also been found in Cook, DuPage, and Will counties. It was already a candidate for the federal endangered species list before the fungus was discovered.