Platarctia parthenos, the St. Lawrence tiger moth, is a moth in the family Erebidae. It was described by Thaddeus William Harris in 1850. It is found in boreal North America, ranging from Alaska to Labrador, south to New Mexico and Arizona in the Rocky Mountains and to North Carolina in the Appalachian Mountains. The habitat consists of riparian areas and mixed hardwood-conifer forests at middle to high elevations.