Canada is restricting U.S. livestock imports after a second screwworm case has been identified in Texas. A second case of the parasite was discovered Friday in a month-old calf in southern Texas. The larva of the screwworm fly feeds on the living tissue of livestock animals, and can be fatal. The USDA says a control zone has been placed around the infected animals. The Canadian Food Inspection Agency says, however, that it will temporarily restrict imports of livestock from affected areas of the U.S.