Louse Flies are parasites, mostly of birds, but some are found on mammals.  They are small, brown, flat flies that are leathery in appearance.  Some are wingless.  They are bloodsuckers.  Females rear one offspring at a time, the larva feeding in utero from special “milk glands.”  The mature larva is "born alive" and immediately pupates in the soil (or on the host in some cases).  Most louse flies are host specific.  There are 28 species in 12 genera in North America.