Flea is the common name for any of the small wingless insects of the order Siphonaptera (some authorities use the name Aphaniptera because it's older, but names above family rank need not follow the ICZN rules of priority, so most taxonomists use the more familiar name). Fleas are external parasites, living by hematophagy off the blood of mammals and birds. Genetic and morphological evidence indicates that they're descendants of the Scorpionfly family Boreidae, which are also flightless; accord… (More on Fleas)