In ordinary language the name is used for any species of Siphonaptera (otherwise known as Aphaniptera), which, though formerly regarded as a suborder of Diptera, are now considered to be a separate order of insects.
All Siphonaptera, of which more than loo species are known, are parasitic on mammals or birds.
With many writers it is customary to treat the fleas as a suborder of Diptera, under the title Aphaniptera or Siphonaptera.
The Siphonaptera appear by the form of the larva and the nature of the metamorphosis to be akin to the Orthorrhapha - in which division they have indeed been included by many students.