 Chewing lice live among the hairs or feathers of their host and feed on skin and debris , while sucking lice pierce the host 's skin and feed on blood and other secretions . They usually spend their whole life on a single host , cementing their eggs , which are known as <unk> , to hairs or feathers . The eggs hatch into nymphs , which moult three times before becoming fully grown , a process that takes about four weeks . 
