Human flea. Light micrograph (LM) of a female human flea (Pulex irratans). Fleas are wingless and flattened from side to side, which makes them difficult to dislodge in hair. They have enlarged hind legs for jumping. Fleas are a vector for various diseases. The female lacks the distinctinctive genitalia of the male flea. Magnification: x15 when printed at 10 centimetres wide.