Also Threadworm, this is a widespread parasitic nematode, usually benign, but having a rural, white trash, skanky stigma. It mates and reproduces in the intestines of several mammals (including us) and the female exits the anus, usually at night, to shed its eggs and expire. The eggs become like dust motes, kids and puppies scratch their butts, the eggs spread into other mammals, until only a thermonuclear device or burning/razing/earth-salting will clear out a heavy infestation.