Flea

For other uses, see Flea (disambiguation).

Flea
Scanning electron microscope (SEM) depiction of a flea
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Subclass:	Pterygota
Infraclass:	Neoptera
Superorder:	Endopterygota
Order:	Siphonaptera Latreille, 1825
Infraorders
Ceratophyllomorpha Hystrichopsyllomorpha Pulicomorpha Pygiopsyllomorpha
Synonyms
Aphaniptera

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

Diagram of a Flea

Fleas are small (1/16 to 1/8-inch (1.5 to 3.3 mm) long), agile, usually dark coloured (for example, 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 (human anatomical terms), permitting easy movement through the hairs or feathers on the host's body (or in the case of humans, under clothes). 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 one of the best jumpers of all known animals (in comparison to body size), second only to the froghopper. The flea body is hard, polished, and covered with many hairs and short spines directed backward, which also assists its movements on the 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 capture them with adhesive tape, crush them between the fingernails, roll them between the fingers, or put them in a fire safe area and burn them with match or lighter. They can also be drowned.

Hooke's drawing of a flea in Micrographia

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, the larvae feed on various organic matter, including the feces of mature fleas. In the pupal phase the larvae are enclosed in a silken, debris-covered cocoon.

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Life cycle and habitat

Fleas are holometabolous insects, going through the three life cycle stages of 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.

Micrograph of a flea larva.

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 and weave a silken cocoon within 1-2 weeks after 3 larval stages. 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[2]. 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 favorable. Female fleas can lay 500 or more eggs over their life, allowing for phenomenal growth rates.

Fleas 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 Hectopsyllidae – sticktight and chigoe fleas ("chiggers" of Latin America)
  • Family Pulicidae – common fleas
• Superfamily Malacopsylloidea
  • Family Malacopsyllidae
  • Family Rhopalopsyllidae – hosts: marsupials
• Superfamily Vermipsylloidea
  • Family Vermipsyllidae – hosts: carnivores
• Superfamily Coptopsylloidea
  • Family Coptopsyllidae
• Superfamily Ancistropsylloidea
  • Family Ancistropsyllidae

Infraorder Pygiopsyllomorpha

• Superfamily Pygiopsylloidea
  • Family Lycopsyllidae
  • Family Pygiopsyllidae
  • Family Stivaliidae

Infraorder Hystrichopsyllomorpha

• Superfamily Hystrichopsylloidea
  • Family Hystrichopsyllidae – hosts: rats and mice. Includes Ctenopsyllidae, Amphipsyllidae
  • Family Chimaeropsyllidae
• Superfamily Macropsylloidea
  • Family Macropsyllidae
• Superfamily Stephanocircidoidea
  • 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

Relationship with host

Flea bites on the back of a human

Flea bite on the waist of a human with no reaction

Fleas attack a wide variety of warm-blooded vertebrates including dogs, cats, humans, chickens, rabbits, squirrels, rats, ferrets, 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 of two bites, 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 be ineffective for itching.

For pets

Flea and tick repellant powder applied to a White German Shepherd dog.

The fleas, their larvae, or their eggs can be controlled with insecticides. Lufenuron is a veterinary preparation (Program) that attacks the larval flea's ability to produce chitin but does not kill fleas. Flea medicines need to be used with care as many, especially the acetylcholinesterase inhibitors, also affect mammals. Popular brands of topicals that do not contain cholinesterase inhibitors include Advantage, Advantix, and Frontline and Frontline PLUS. In 2008, three next-generation flea products reached the market: Promeris, Comfortis, and Vectra 3D.

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 flea trap and mop up newly hatched fleas. The environment should be treated with a fogger or spray insecticide 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, but you must immediately dispose of the vacuum bag afterwards.

Flea "dirt" in the fur of a cat is actually excess blood from the host consumed by the adult flea and passed as feces.

Diatomaceous earth can also be used as an effective home flea treatment in lieu of acetylcholinesterase inhibitory treatments or insecticides which carry with them a risk of poisoning for both humans and animals. Diatomaceous earth absorbs lipids from the cuticle, the waxy outer layer of insects' exoskeletons, causing them to dehydrate. Purchasable from most gardening suppliers or online retailers, it can be evenly distributed around the house (especially in corners and near furniture) with any type of shaker (salt shaker, spice shaker, etc.) and then vacuumed away after about 7 days. Diatomaceous earth also has the added benefit of killing many other types of insects that might be residing in your house.

Dried pennyroyal has been suggested as a natural flea control, but is not recommended in homes with pets due to its high toxicity to mammals.

Borax is sold as a "Natural Laundry Booster" and can also be used as another home treatment for flea infestations. Borax contains boric acid which kills fleas by dehydrating them.

Using dehumidifiers with air conditioning and vacuuming all may interrupt the flea life cycle. Humidity is critical to flea survival. Eggs need relative humidity of at least 70-75 percent to hatch, and larvae need at least 50 percent humidity to survive. In humid areas, about 20 percent of the eggs survive to adulthood; in arid areas, less than five percent complete the cycle. Fleas thrive at higher temperatures, but need 70° to 90°F to survive. Lower temperatures slow down or completely interrupt the flea lifecycle. A laboratory study done at the University of California showed that vacuuming catches about 96 percent of adult fleas. A combination of controlled humidity, temperature and vacuuming should eliminate fleas from an environment, and altering even one of these environmental factors may be enough to drastically lower and eliminate an infestation.

See also

• Anti-itch drug
• Bubonic plague
• Cat flea
• Use of DNA in forensic entomology

External links

• Template:Dmoz
• Fleas – least toxic control - alternatives to pesticides fact sheet from PAN UK.
• How to get rid of fleas
• Flea Pest Control Information - National Pesticide Information Center
• Advice about fleas from the Berkeley Parents Network
• Links to flea bite pictures (Hardin MD/Univ of Iowa)
• Good Neighbors An essay on the natural history of the flea
• Sand Flea Bite Picture
• Fleas As Weapon
• Fleas chapter in United States Environmental Protection Agency‎ and University of Florida/Institute of Food and Agricultural Sciences National Public Health Pesticide Applicator Training Manual