Head lice have adapted to live on the scalp of humans exclusively. This is where the head lice find a temperature of about 86°F / 30°C and a humidity of around 90%, and lots of food, which overall gives them the optimal living conditions. By means of their very specialized mouthparts the head lice feed from the blood, which they suck from the skin on the scalp. The blood passes through the intestine of the louse and the nutrition and liquid are absorbed during this process. The leftovers are excreted as small dry fecal pellets.