Crews in Southern Mississippi Tuesday were removing thousands of dead nutria – rat-like rodents originally from South America – which drowned and washed up on the beaches in the aftermath of Hurricane Isaac, NBC News reported. "Estimates are there will be over 20,000 carcasses," said Robbie Wilbur, spokesman for the state's department of environmental quality. The rotting carcasses are a health hazard as they blow up and eventually burst open. With their orange front teeth and rat like tail, nutria wreak ecological havoc on native wetland vegetation and contribute to coastal erosion by digging into thin soils and eating roots of marsh vegetation. They’re an invasive species – released in Louisiana and Mississippi in the 1930s by fur trappers. Their population exploded–nutria reach sexual maturity at just four months old, and females are able to breed within 48 hours of giving birth to a litter – when the demand for their fur decreased drastically in the 1980’s. Still, Isaac did little to reduce the number of nutria – their population is estimated at several million.