Fleas are blood sucking insects belonging to the order Siphonaptera. Fleas are thought to be closely related to Diptera(True Flies). Although ectoparasites the wings of fleas have been lost during their evolution but it has been suggested that muscles that may have been used for flight are now used to power the well developed rear legs. The rear legs arise from the metathorax and this area is well developed as a consequence of this. In contrast to Anoplura fleas are flattened laterally allowing them to travel quickly through host hair. Morphological adaptations other than lateral flattening include recessed antennae-long antennae would only serve to obstruct a fleas passage- and backward pointing setae, these anchor the flea against surrounding hairs if attempts are made to remove them.