laid. A nymph is an immature louse that hatches from the egg. Immediately after hatching it starts feeding on the host's blood and then returns to the clothing until the next blood-meal. The nymph will molt three times before the adult louse emerges. The nymph usually takes 9–12 days to develop into an adult louse. The adult body louse is about 2.5–3.5 mm long, and like a nymph it has six legs. It is wingless and is tan to grayish-white in color. The two P. humanus subspecies are morphologically quite identical. Their heads are short with two antennae that are split into five segments each, compacted thorax, seven segmented abdomen with lateral paratergal plates. Origins The body louse diverged from the head louse around 170,000 years ago, establishing the latest date for the adoption of clothing by humans. Body lice were first described by Carl Linnaeus in the 10th edition of Systema Naturae. The human body louse had its genome sequenced in 2010, and at that time it had the smallest known insect genome. The body louse belongs to the phylum Arthropoda, class Insecta, order Phthiraptera and family Pediculidae. There are roughly 5,000 species of lice described, 4,000 are parasitizing birds, while additional 800 are special parasites of mammals worldwide. Signs and symptoms Since an infestation can include thousands of lice, with each of them biting five times a day, the bites can cause strong itching, especially at the beginning of the infestation, that can result in skin excoriations and secondary infections. If an individual is exposed to a long-term infestation, he or she may experience apathy, lethargy and fatigue. Treatment In principle, body louse infestations can be controlled by periodically changing clothes and bedding. Thereafter, clothes, towels, and bedding should be washed in hot water (at least ) and dried using a hot cycle. The itching can be treated with topical and systemic corticosteroids and antihistamines. In case of secondary infections, antibiotics can be used to control the bacterial infection. When regular changing of clothes and bedding is not possible, the infested items could be treated with insecticides. Diseases caused Unlike other species of lice, body lice can also act as vectors of disease. The most important pathogens which are transmitted by them are Rickettsia prowazekii (causes epidemic typhus), Borrelia recurrentis (causes relapsing fever), and Bartonella quintana (causes trench fever). Epidemic typhus can be treated with one dose of