Fleas are small, wingless, laterally compressed blood sucking insects. Most fleas are mammalian ectoparasites but a few parasitize birds. About 2400 species are known. Like most parasites, fleas are highly derived and specialized. The mouthparts are adapted for piercing and sucking and mandibles are lacking. The cuticle is sclerotized and hard and the entire body surface is protected by sclerites.