Head lice live on the scalp. They have evolved over thousands of years and have adapted to an environment that is very, very specific to a certain level of humidity, temperature, and the presence of human blood that can all be found on the human head. That means they don’t venture from that. They live almost exclusively on the human head because they can suck blood for their food, they stay warm because the head is very warm, there is an insulating factor of hair, they lay their eggs, and the eggs get glued to their hair. They are very comfortable on the human head. If they are off the head, they don’t last very long. They die within 24-48 hours, within a very short period of time.