First thing's first. Sea lice aren't lice at all. They're tiny baby jellyfish, so small you can't even see them -- about the size of a grain of pepper. And just like their grownup counterparts ...

Head lice feed only on humans. Head lice are blood-sucking insects about the size of a sesame seed and are tan to grayish-white in color. They attach themselves to the skin of the head (scalp ...