Fossil range: Cretaceous–Recent 
|Scanning electron microscope (SEM) depiction of a flea|
Flea is the common name for insects of the order Siphonaptera which are wingless insects whose mouthparts are adapted for piercing skin and sucking blood. Fleas are external parasites, living by hematophagy off the blood of mammals (including humans) and birds.
In the past, it was most commonly supposed that fleas had evolved from the flies (Diptera), based on similarities of the larvae. (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). 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 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 flea species include:
Fleas are small (1/16 to 1/8-inch (1.5 to 3.3 mm) long), agile, usually dark colored (for example, the reddish-brown of the cat flea), wingless insects with tube-like mouth-parts 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 attempts to eliminate them such as scratching. 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 burn them with match or lighter. They can also be drowned.
Fleas lay tiny white oval shaped eggs. Their larvae are small and pale with bristles covering their worm-like body. They lack 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.
Fleas are holometabolous insects, going through the four life cycle stages of egg, 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 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. 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.
Adult female rabbit fleas, Spilopsyllus cuniculi, can detect the changing levels of cortisol and corticosterone, hormones in the rabbit's blood that indicate she is getting close to giving birth. This triggers sexual maturity in the fleas and they start producing eggs. As soon as the baby rabbits are born, the fleas make their way down to them and once on board they start feeding, mating, and laying eggs. After 12 days, the adult fleas make their way back to the mother. They complete this mini-migration every time she gives birth.
Fleas are related to mecoptera, winged insects with good eyesight. The flightless boreid (snow scorpionfly) with its rudimentary wings seems to be close to the common ancestor of the 2000 or so 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 are 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.
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 (similar to a mosquito sting). 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.
The itching associated with flea bites can be treated with anti-itch creams, usually antihistaminics or hydrocortisone. Calamine lotion has been shown to be effective for itching . Also a bath with TCP and bicarbonate of soda has been found to reduce the itching .
Modern flea control is approached using Integrated Pest Management (IPM) protocols at the host (pet) level. IPM is achieved by targeting fleas at at least two separate life stages, with at least two separate molecules. This is typically achieved using an adulticide to kill adult fleas and a insect development inhibitor (IDI), like lufenuron, or insect growth regulator (IGR), like methoprene, to prevent development of immature stages. 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, Frontline and Frontline PLUS. In 2008, three next-generation flea products reached the market: Promeris, Comfortis, and Vectra 3D.
Cedar oil, a non-toxic natural substance. has been proven effective in the eradication of infestations in pets and is non-toxic. The U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) have approved formulations in the U.S., including Cedarcide and Greenlight 3-Step Flea & Tick Control Program.
Since more that three quarters of a flea's life is spent somewhere other than on the pet, it is not adequate to treat only the pet for fleas. It is important to treat the animal's environment also. Thorough vacuuming, washing linens in hot water, and treating all pets in the household are essential. 
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 the vacuum bag must be disposed of immediately afterwards.
Diatomaceous earth can also be used as a 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 however is toxic to pets and people when inhaled and is therefore not recommended.
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, but its safety for pets is untested. .
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(21° to 32°C) to survive. Lower temperatures slow down or completely interrupt the flea life-cycle. 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.
Mark but this flea, and mark in this,
How little that which thou deniest me is;
It suck'd me first, and now sucks thee,
And in this flea our two bloods mingled be.
Thou know'st that this cannot be said
A sin, nor shame, nor loss of maidenhead;
Yet this enjoys before it woo,
And pamper'd swells with one blood made of two;
And this, alas! is more than we would do.
O stay, three lives in one flea spare,
Where we almost, yea, more than married are.
This flea is you and I, and this
Our marriage bed, and marriage temple is.
Though parents grudge, and you, we're met,
And cloister'd in these living walls of jet.
Though use make you apt to kill me,
Let not to that self-murder added be,
And sacrilege, three sins in killing three.
Cruel and sudden, hast thou since
Purpled thy nail in blood of innocence?
Wherein could this flea guilty be,
Except in that drop which it suck'd from thee?
Yet thou triumph'st, and say'st that thou
Find'st not thyself nor me the weaker now.
'Tis true; then learn how false fears be;
Just so much honour, when thou yield'st to me,
Will waste, as this flea's death took life from thee.
This article is from the 1911 Encyclopaedia Britannica. Medical science has made many leaps forward since it has been written. This is not a site for medical advice, when you need information on a medical condition, consult a professional instead.
FLEA (0. Eng. fleah, or flea, cognate with flee, to run away from, to take flight), a name typically applied to Pulex irritans, a well-known blood-sucking insect-parasite of man and other mammals, remarkable for its powers of leaping, and nearly cosmopolitan. In ordinary language the name is used for any species of Siphonaptera (otherwise known as Aphaniptera), which, though formerly regarded as a suborder of Diptera, are now considered to be a separate order of insects. All Siphonaptera, of which more than loo species are known, are parasitic on mammals or birds. The majority of the species belong to the family Pulicidae, of which P. irritans maybe taken as the type; but the order also includes the Sarcopsyllidae, the females of which fix themselves firmly to their host, and the Ceratopsyllidae, or bat-fleas.
Fleas are wingless insects, with a laterally compressed body, small and indistinctly separated head, and short thick antennae situated in cavities somewhat behind and above the simple eyes, which are always minute and sometimes absent. The structure of the mouth-parts is different from that seen in any other insects. The actual piercing organs are the mandibles, while the upper lip or labrum forms a sucking tube. The maxillae are not piercing organs, and their function is to protect the mandibles and labrum and separate the hairs or feathers of the host. Maxillary and labial palpi are also present, and the latter, together with the labrum or lower lip, form the rostrum.
Fleas are oviparous, and undergo a very complete metamorphosis. The footless larvae are elongate, worm-like and very active; they feed upon almost any kind of waste animal matter, and when full-grown form a silken cocoon. The human flea is considerably exceeded in size by certain other species found upon much smaller hosts; thus the European Hystrichopsylla talpae, a parasite of the mole, shrew and other small mammals, attains a length of 5z millimetres; another large species infests the Indian porcupine. Of the Sarcopsyllidae the best known species is the "jigger" or "chigoe" (Dermatophilus penetrans), indigenous in tropical South America and introduced into West Africa during the second half of last century. Since then this pest has spread across the African continent and even reached Madagascar. The impregnated female jigger burrows into the feet of men and dogs, and becomes distended with eggs until its abdomen attains the size and appearance of a small pea. If in extracting the insect the abdomen be ruptured, serious trouble may ensue from the resulting inflammation. At least four species of fleas (including Pulex irritans) which infest the common rat are known to bite man, and are believed to be the active agents in the transmission of plague from rats to human beings. (E. E. A.) Fleche (French for "arrow"), the term generally used in French architecture for a spire, but more especially employed to designate the timber spire covered with lead, which was erected over the intersection of the roofs over nave and transepts; sometimes these were small and unimportant, but in cathedrals they were occasionally of large dimensions, as in the fleche of Notre-Dame, Paris, where it is nearly ioo ft. high; this, however, is exceeded by the example of Amiens cathedral, which measures 148 ft. from its base on the cresting to its finial.
Flechier, Esprit (1632-1710), French preacher and author, bishop of Nimes, was born at Pernes, department of Vaucluse, on the 10th of June 1632. He was brought up at Tarascon by his uncle, Hercule Audiffret, superior of the Congregation des Doctrinaires, and afterwards entered the order. On the death of his uncle, however, he left it, owing to the strictness of its rules, and went to Paris, where he devoted himself to writing poetry. His French poems met with little success, but a description in Latin verse of a tournament (carrousel, circus regius), given by Louis XIV. in 1662, brought him a great reputation. He subsequently became tutor to Louis Urbain Lefevre de Caumartin, afterwards intendant of finances and counsellor of state, whom he accompanied to Clermont-Ferrard (q.v.), where the king had ordered the Grands Jours to be held (1665), and where Caumartin was sent as representative of the sovereign. There Flechier wrote his curious Meinoires sur les Grand Jours tenus d Clermont, in which he relates, in a half romantic, half historical form, the proceedings of this extraordinary court of justice. In 1668 the duke of Montausier procured for him the post of lecteur to the dauphin. The sermons of Flechier increased his reputation, which was afterwards raised to the highest pitch by his funeral orations. The most important are those on Madame de Montausier (1672), which gained him the membership of the Academy, the duchesse d'Aiguillon (1675), and, above all, Marshal Turenne (1676). He was now firmly established in the favour of the king, who gave him successively the abbacy of St Severin, in the diocese of Poitiers, the office of almoner to the dauphiness, and in 1685 the bishopric of Lavaur, from which he was in 1687 promoted to that of Nimes. The edict of Nantes had been repealed two years before; but the Calvinists were still very numerous at Nimes. Flechier, by his leniency and tact, succeeded in bringing over some of them to his views, and even gained the esteem of those who declined to change their faith. During the troubles in the Cevennes (see Huguenots) he softened to the utmost of his power the rigour of the edicts, and showed himself so indulgent even to what he regarded as error, that his memory was long held in veneration amongst the Protestants of that district. It is right to add, however, that some authorities consider the accounts of his leniency to have been greatly exaggerated, and even charge him with going beyond what the edicts permitted. He died at Montpellier on the 16th of February 1710. ' Pulpit eloquence is the branch of belles-lettres in which Flechier excelled. He is indeed far below $ossuet, whose robust and sublime genius had no rival in that age; he does not equal Bourdaloue in earnestness of thought and vigour of expression; nor can he rival the philosophical depth or the insinuating and impressive eloquence of Massillon. But he is always ingenious, often witty, and nobody has carried farther than he the harmony of diction, sometimes marred by an affectation of symmetry and an excessive use of antithesis. His two historical works, the histories of Theodosius and of Ximenes, are more remarkable for elegance of style than for accuracy and comprehensive insight.
The last complete edition of Flechier's works is by J. P. Migne (Paris, 1856); the Memoires sur les Grands Jours was first published in 1844 by B. Gonod (2nd ed. as Mem. sur les Gr. J. d'Auvergne, with notice by Sainte-Beuve and an appendix by M. Cheruel, 1862). His chief works are: Histoire de Theodose le Grand, Oraisons funebres, Histoire du Cardinal Ximenes, Sermons de morale, Panegyriques des saints. He left a portrait or caractere of himself, addressed to one of his friends. The Life of Theodosius has been translated into English by F. Manning (1693), and the "Funeral Oration of Marshal Turenne" in H. C. Fish's History and Repository of Pulpit Eloquence (ii., 1857). On Flechier generally see Antonin V. D. Fabre, La Jeunesse de Flechier (1882), and Adolphe Fabre, Flechier, orateur (1886); A. Delacroix, Hist. de Flechier (1865).
<< John Flaxman
David at the cave of Adullam thus addressed his persecutor Saul (1Sam 24:14): "After whom is the king of Israel come out? after whom dost thou pursue? after a dead dog, after a flea?" He thus speaks of himself as the poor, contemptible object of the monarch's pursuit, a "worthy object truly for an expedition of the king of Israel with his picked troops!" This insect is in Eastern language the popular emblem of insignificance. In 1Sam 26:20 the LXX. read "come out to seek my life" instead of "to seek a flea."
what mentions this? (please help by turning references to this page into wiki links)
There are several types of fleas including the dog flea, cat flea, human flea, northern rat flea, and the oriental rat flea. During the Middle Ages, the oriental rat flea that spread a bacteria that caused the Bubonic Plague, also known as the Black Death or Black Plague, a huge epidemic the size of today's bird flu. The oriental rat flea would become infected by the bacteria: yersinia pestis . After infected the bacteria grew inside of the flea eventually blocking the path to their stomach. Because of this the flea was always hungry. When the flea would bite a human it opened up the skin and since the stomach of the flea was blocked, the blood from the human was heaved up back into the human, but only this time it was infected with the Bubonic plague bacteria.