Between 1735 and 1758, the Swedish naturalist Carl Linnaeus first classified insects, doing so on the basis of their wing structure.
One of the seven orders into which he divided them was "Aptera", meaning wingless, a group in which as well as fleas, he included spiders, woodlice and myriapods.
It wasn't until 1810 that the French zoologist Pierre André Latreille reclassified the insects on the basis of their mouthparts as well as their wings, splitting Aptera into Thysanura (silverfish), Anoplura (sucking lice) and Siphonaptera (fleas), at the same time separating off the arachnids and crustaceans into their own subphyla.
The group's name, Siphonaptera, is zoological Latin from the Greek siphon (a tube) and aptera (wingless).

Fleas are related to the Diptera (true flies) and the Mecoptera (scorpion flies) as shown in the cladogram, based on a 2008 analysis of four loci (18S and 28S ribosomal DNA, cytochrome oxidase II, and elongation factor 1-alpha) for 128 flea taxa from around the world.
The Boreidae (snow scorpionflies) are the sister clade to the Siphonaptera.

Amphies.
= Amphiesmenoptera
Fossils of wingless "pre-fleas" with siphonate (sucking) mouthparts from the middle Jurassic to early Cretaceous have been found in northeastern China.
These belonged to three proposed extinct families, the Pseudopulicidae, the Saurophthiridae, and the Tarwiniidae.
The last common ancestor of modern Siphonaptera separated from the Mecoptera during the early Cretaceous.
Most flea families formed after the end of the Cretaceous (in the Paleogene and onwards).
Fleas probably arose in the southern continental area of Gondwana, and migrated rapidly northwards from there.
They most likely evolved with mammal hosts, only later moving to birds.

Siphonaptera is a relatively small order of insects: members of the order undergo complete metamorphosis and are secondarily wingless (their ancestors had wings which modern forms have lost).
In 2005, Medvedev listed 2005 species in 242 genera, and despite subsequent descriptions of new species, bringing the total up to around 2500 species, this is the most complete database available.
The order is divided into four infraorders and eighteen families.
Some families are exclusive to a single host group; these include the Malacopsyllidae (armadillos), Ischnopsyllidae (bats) and Chimaeropsyllidae (elephant shrews).

Many of the known species are little studied.
Some 600 species (a quarter of the total) are known from a single record from a single host.
Over 94% of species are associated with mammalian hosts, and only about 3% of species can be considered to be specific parasites of birds.
The fleas on birds are thought to have originated from mammalian fleas; at least sixteen separate groups of fleas switched to avian hosts during the evolutionary history of the Siphonaptera.
Occurrences of fleas on reptiles is accidental, and fleas have been known to feed on the hemolymph (bloodlike body fluid) of ticks.

Flea phylogeny was long neglected, the discovery of homologies with the parts of other insects being made difficult by their extreme specialization.
Whiting and colleagues prepared a detailed molecular phylogeny in 2008, with the basic structure shown in the cladogram.
The Hectopsyllidae, including the harmful chigoe flea or jigger, is sister to the rest of the Siphonaptera.
Between 1735 and 1758, the Swedish naturalist Carl Linnaeus first classified insects, doing so on the basis of their wing structure. One of the seven orders into which he divided them was "Aptera", meaning wingless, a group in which as well as fleas, he included spiders, woodlice and myriapods. It wasn't until 1810 that the French zoologist Pierre André Latreille reclassified the insects on the basis of their mouthparts as well as their wings, splitting Aptera into Thysanura (silverfish), Anoplura (sucking lice) and Siphonaptera (fleas), at the same time separating off the arachnids and crustaceans into their own subphyla. The group's name, Siphonaptera, is zoological Latin from the Greek siphon (a tube) and aptera (wingless).
Fleas are related to the Diptera (true flies) and the Mecoptera (scorpion flies) as shown in the cladogram, based on a 2008 analysis of four loci (18S and 28S ribosomal DNA, cytochrome oxidase II, and elongation factor 1-alpha) for 128 flea taxa from around the world. The Boreidae (snow scorpionflies) are the sister clade to the Siphonaptera.
Amphies. = Amphiesmenoptera
Fossils of wingless "pre-fleas" with siphonate (sucking) mouthparts from the middle Jurassic to early Cretaceous have been found in northeastern China. These belonged to three proposed extinct families, the Pseudopulicidae, the Saurophthiridae, and the Tarwiniidae. The last common ancestor of modern Siphonaptera separated from the Mecoptera during the early Cretaceous. Most flea families formed after the end of the Cretaceous (in the Paleogene and onwards). Fleas probably arose in the southern continental area of Gondwana, and migrated rapidly northwards from there. They most likely evolved with mammal hosts, only later moving to birds.
Siphonaptera is a relatively small order of insects: members of the order undergo complete metamorphosis and are secondarily wingless (their ancestors had wings which modern forms have lost). In 2005, Medvedev listed 2005 species in 242 genera, and despite subsequent descriptions of new species, bringing the total up to around 2500 species, this is the most complete database available. The order is divided into four infraorders and eighteen families. Some families are exclusive to a single host group; these include the Malacopsyllidae (armadillos), Ischnopsyllidae (bats) and Chimaeropsyllidae (elephant shrews).
Many of the known species are little studied. Some 600 species (a quarter of the total) are known from a single record from a single host. Over 94% of species are associated with mammalian hosts, and only about 3% of species can be considered to be specific parasites of birds. The fleas on birds are thought to have originated from mammalian fleas; at least sixteen separate groups of fleas switched to avian hosts during the evolutionary history of the Siphonaptera. Occurrences of fleas on reptiles is accidental, and fleas have been known to feed on the hemolymph (bloodlike body fluid) of ticks.
Flea phylogeny was long neglected, the discovery of homologies with the parts of other insects being made difficult by their extreme specialization. Whiting and colleagues prepared a detailed molecular phylogeny in 2008, with the basic structure shown in the cladogram. The Hectopsyllidae, including the harmful chigoe flea or jigger, is sister to the rest of the Siphonaptera.
Flea