Scabies are 8-legged critters that burrow into the upper layer of your skin and lay eggs. When the eggs hatch, the mites climb to the surface of your skin, where they spread to other parts of your body. A severe form of scabies called “crusted scabies” (or Norwegian crusted scabies) sometimes happens in people who have weakened immune systems. It gets its name from the thick crusts of skin that form from large numbers of scabies mites and eggs