Human fleas. Light micrograph (LM) of a male (left) and 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 genitalia of male flea are complex with claspers and a penis (aedeagus) which is coiled like a spring, so the male is easy to recognise. Magnification: x10 when printed at 10 centimetres wide.