Flea

# Overview
Flea is the common name for any of the small wingless insects of the order Siphonaptera (some authorities use the name Aphaniptera because it is older, but names above family rank need not follow the ICZN rules of priority, so most taxonomists use the more familiar name). Fleas are external parasites, living by hematophagy off the blood of mammals and birds. Genetic and morphological evidence indicates that they are descendants of the Scorpionfly family Boreidae, which are also flightless; accordingly it is possible that they will eventually be reclassified as a suborder within the Mecoptera. In the past, however, it was most commonly supposed that fleas had evolved from the flies (Diptera), based on similarities of the larvae. In any case, all these groups seem to represent a clade of closely related insect lineages, for which the names Mecopteroidea and Antliophora have been proposed.
Some well known flea species include:
- Cat flea (Ctenocephalides felis),
- Dog flea (Ctenocephalides canis),
- Human flea (Pulex irritans),
- Northern rat flea (Nosopsyllus fasciatus),
- Oriental rat flea (Xenopsylla cheopis).

# Morphology and behavior
Fleas are small (1/16 to 1/8-inch (1.5 to 3.3 mm) long), agile, usually dark coloured (e.g. the reddish-brown of the cat flea), wingless insects with tube-like mouthparts adapted to feeding on the blood of their hosts. Their bodies are laterally compressed, (i.e., flattened side to side) permitting easy movement through the hairs (or feathers etc.) on the host's body. Their legs are long, the hind pair well adapted for jumping (vertically up to seven inches (18 cm); horizontally thirteen inches (33 cm)) - around 200 times their own body length, making the flea the best jumper out of all animals (in comparison to body size). The flea body is hard, polished, and covered with many hairs and short spines directed backward, allowing the flea a smooth passage through the hairs of its host. Its tough body is able to withstand great pressure, likely an adaptation to survive scratching etc. Even hard squeezing between the fingers is normally insufficient to kill the flea; it may be necessary to crush them between the fingernails or roll them between the fingers.
Fleas lay tiny white oval shaped eggs. Their larvae are small and pale with bristles covering their worm-like body. They are without eyes, and have mouthparts adapted to chewing. While the adult flea's diet consists solely of blood, their larvae feed on various organic matter including the feces of mature fleas. In the pupae phase the larvae are enclosed in a silken, debris covered cocoon.

# Life cycle and habitat
Fleas are holometabolous insects, going through the four life cycle stages of embryo, larva, pupa and imago (adult). The flea life cycle begins when the female lays after feeding. Adult fleas must feed on blood before they can become capable of reproduction. Eggs are laid in batches of up to 20 or so, usually on the host itself, which easily roll onto the ground. As such, areas where the host rests and sleeps become one of the primary habitats of eggs and developing fleas. The eggs take around two days to two weeks to hatch.
Flea larvae emerge from the eggs to feed on any available organic material such as dead insects, feces and vegetable matter. They are blind and avoid sunlight, keeping to dark places like sand, cracks and crevices, and bedding. Given an adequate supply of food, larvae should pupate within 1-2 weeks. After going through three larval stages they spin a silken cocoon. After another week or two the adult flea is fully developed and ready to emerge from the cocoon. They may however remain resting during this period until they receive a signal that a host is near - vibrations (including sound), heat and carbon dioxide are all stimuli indicating the probable presence of a host. Fleas are known to overwinter in the larval or pupal stages.
Once the flea reaches adulthood its primary goal is to find blood - adult fleas must feed on blood in order to reproduce. Adult fleas only have around a week to find food once they emerge, though they can survive two months to a year between meals. A flea population is unevenly distributed, with 50 percent eggs, 35 percent larvae, 10 percent pupae and 5 percent adults. Their total life cycle can take as little as two weeks, but may be lengthened to many months if conditions are favourable. Female fleas can lay 500 or more eggs over their life, allowing for phenomenal growth rates.

# Evolution and classification
Fleas are apparently related to scorpionflies, winged insects with good eyesight. The flightless snow flea with its rudimentary wings seems to be close to the common ancestor of the 2000 or so currently known varieties of flea, which split off in many directions around 160 million years ago. Their evolution continued to produce adaptations for their specialized parasitic niche, such that they now have no wings and their eyes are covered over. The large number of flea species may be attributed to the wide variety of host species they feed on, which provides so many specific ecological niches to adapt to.
Flea systematics is not entirely fixed. While compared to many other insect groups fleas have been studied and classified fairly thoroughly, details still remain to be learned about the evolutionary relationships among the different flea lineages.
Infraorder Pulicomorpha
- Superfamily Pulicoidea
Family Tungidae  sticktight and chigoe fleas ("chiggers" of Latin America)
Family Pulicidae  common fleas
- Family Tungidae  sticktight and chigoe fleas ("chiggers" of Latin America)
- Family Pulicidae  common fleas
- Superfamily Malacopsylloidea
Family Malacopsyllidae
Family Rhopalopsyllidae  hosts: marsupials
- Family Malacopsyllidae
- Family Rhopalopsyllidae  hosts: marsupials
- Superfamily Vermipsylloidea
Family Vermipsyllidae  hosts: carnivores
- Family Vermipsyllidae  hosts: carnivores
- Superfamily Coptopsylloidea
Family Coptopsyllidae
- Family Coptopsyllidae
- Superfamily Ancistropsylloidea
Family Ancistropsyllidae
- Family Ancistropsyllidae
Infraorder Pygiopsyllomorpha
- Superfamily Pygiopsylloidea
Family Lycopsyllidae
Family Pygiopsyllidae
Family Stivaliidae
- Family Lycopsyllidae
- Family Pygiopsyllidae
- Family Stivaliidae
Infraorder Hystrichopsyllomorpha
- Superfamily Hystrichopsylloidea
Family Hystrichopsyllidae  hosts: rats and mice. Includes Ctenopsyllidae, Amphipsyllidae
Family Chimaeropsyllidae
- Family Hystrichopsyllidae  hosts: rats and mice. Includes Ctenopsyllidae, Amphipsyllidae
- Family Chimaeropsyllidae
- Superfamily Macropsylloidea
Family Macropsyllidae
- Family Macropsyllidae
- Superfamily Stephanocircidoidea
Family Stephanocircidae - hosts: rodents
- Family Stephanocircidae - hosts: rodents
Infraorder Ceratophyllomorpha
- Superfamily Ceratophylloidea
Family Ceratophyllidae - hosts: rodents and birds. Includes Dolichopsyllidae
Family Leptopsyllidae  hosts: mice and rats
Family Ischnopsyllidae  hosts: bats
Family Xiphiopsyllidae
- Family Ceratophyllidae - hosts: rodents and birds. Includes Dolichopsyllidae
- Family Leptopsyllidae  hosts: mice and rats
- Family Ischnopsyllidae  hosts: bats
- Family Xiphiopsyllidae

# Relationship with host
Fleas attack a wide variety of warm-blooded vertebrates including dogs, cats, humans, chickens, rabbits, squirrels, rats and mice. Fleas are a nuisance to their hosts, causing an itching sensation which in turn may result in the host attempting to remove the pest by biting, pecking, scratching etc the vicinity of the parasite. Fleas are not simply a source of annoyance, however. Some people and animals suffer allergic reactions to flea saliva resulting in rashes. Flea bites generally result in the formation of a slightly-raised swollen itching spot with a single puncture point at the center. The bites often appear in clusters or lines, and can remain itchy and inflamed for up to several weeks afterwards. Fleas can also lead to hair loss as a result of frequent scratching and biting by the animal, and can cause anemia in extreme cases.
Besides the problems posed by the creature itself, fleas can also act as a vector for disease.  For example, fleas transmitted the bubonic plague between rodents and humans by carrying Yersinia pestis bacteria. Murine typhus (endemic typhus) fever, and in some cases Hymenolepiasis (tapeworm) can also be transmitted by fleas.

# Flea treatments

## For humans
The itching associated with flea bites can be treated with anti-itch creams, usually antihistaminics or hydrocortisone. Calamine lotion has been shown to lack any effect on itching.

## For pets
The fleas, their larvae, or their eggs can be controlled with insecticides. Lufenuron and fipronil are popular veterinary preparation that attacks the larval flea's ability to produce chitin. Flea medicines need to be used with care as many, especially the acetylcholinesterase inhibitors, also affect mammals.  Popular brands include Bayer Advantage, Advantix, and Frontline.

## For the home
Combating a flea infestation in the home takes patience as for every flea found on an animal there are many more developing in the home. A spot-on insecticide, such as Advantage, Frontline or Revolution will kill the fleas on the pet and in turn the pet itself will be a roving fleatrap and mop up newly hatched fleas. The environment ought to be treated with a fogger containing an insect growth regulator, such as pyriproxyfen or methoprene to kill eggs and pupae, which are quite resistant against insecticides. Frequent vacuuming is also helpful.
Even though organophosphate-based insecticides are still sold as flea collars, flea powders and flea shampoos those are not recommended. Many strains of insects have become resistant against that class of compounds, and they display an unacceptably high level of toxicity against mammals.

# Other
The Moche people of ancient Peru worshipped nature. They placed emphasis on animals and even depicted fleas in their art.