The flesh-eating pest that once cost ranchers millions is back

It's back: For the first time since 1982, the New World screwworm has been found in U.S. cattle.

The flesh-eating parasitic fly, which was eradicated from American cattle herds almost 50 years ago, has been detected in three cows, one dog and a goat, prompting Canada to restrict cattle imports from the United States and raising the specter of a wider outbreak.

The New World screwworm was a massive problem in U.S. cattle herds for much of the 20th century, killing countless cows and costing the industry hundreds of millions of dollars.