Non-sentient humanoid race, frightened by normal light and visible only under ultraviolet with dark skin topped by glowing blue veins, that uses a DNA strand implant in an alien host's thymus to reproduce via genetic metamorphosis. Onset of symptoms can vary from days to an hour: blood chemistry changes, the skin develops blotchy blue surface veins and radiates its own light, and the middle three fingers fuse. With the immune system attacked, first the blood pressure and then body temperature drops.