Parasitic insects are organisms that feed off of other living creatures, often without the host's knowledge. LICE and nits are two examples of parasitic insects. LICE are small, wingless insects that live on the skin of mammals and birds, while nits are the eggs of LICE that are laid on the hair or feathers of the host. Both LICE and nits can cause irritation and discomfort to the host, and can be difficult to get rid of.