 Flea larvae are worm-like with no limbs; they have chewing mouthparts and feed on organic debris left on their host's skin.The Siphonaptera are most closely related to the snow scorpionflies (known as snow fleas in the UK) in the family Boreidae, placing them within the Endopterygote insect order Mecoptera.Fleas arose in the early Cretaceous, most likely as ectoparasites of mammals, before moving on to other groups, including birds.