Head lice live on the human scalp. They have evolved over thousands of years and have adapted to an environment that is very specific to a certain level of humidity, temperature, and the presence of human blood. That means they don’t venture from that. They live almost exclusively on the human head. They suck blood for 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 the hair. They are very comfortable. If they are off the head, they don’t last long. They die within a very short period of time-24 to 48 hours.