Two more cases of the New World screwworm have been confirmed in Texas, demonstrating the difficulty of stopping the spread of a pest that could potentially devastate the nation's cattle industry, the U.S. Department of Agriculture announced Monday.

The screwworm is actually a fly, which produces a larva that eats live flesh instead of dead material. Females lay their eggs in open wounds of any warm-blooded animal, such as cattle, but wildlife, pets and occasionally even humans can be infested.

The USDA said the new cases were found in a calf and a dog, hundreds of miles apart in La Salle and Andrews counties. That brings the total number of confirmed cases to four. The screwworm was first discovered in a 3-week-old calf last week, and a second case was found only miles away in a young calf.