The northern rat flea (Nosopsyllus fasciatus) is a species of flea found on domestic rats and house mice. Northern rat fleas are external parasites, living by hematophagy off the blood of rodents. It is the most widely spread of its genus, having originated in Europe, but has been transported to temperate regions all over the world.
N. fasciatus has an elongated body, 3 to 4 mm in length. It has a pronotal ctenidium with 18 to 20 spines (on the first thoracic tergite), but lacks a genal ctenidium. The northern rat flea has eyes and a row of three setae below it on the heads. Both sexes have a prominent tubercle on the front of the head. The hind femur has three to four bristles on the inner surface.
Though the northern rat flea primarily parasitises the Norway rat, Rattus norvegicus, it has occasionally been observed feeding on humans and wild rodents. It is a minor vector for plague and is known to be a host of the rat tapewormHymenolepis diminuta in South America, Europe, and Australia.
(From Wikipedia, May 2015)