Flea

Flea Fossil range: Cretaceous–Recent PreЄ Є O S D C P T J K Pg N [1]
Scanning electron microscope (SEM) depiction of a flea
Scientific classification
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 insects of the order Siphonaptera which are wingless insects with mouthparts 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:

• Cat flea (Ctenocephalides felis)
• Dog flea (Ctenocephalides canis)
• Human flea (Pulex irritans)
• Moorhen flea Dasypsyllus gallinulae
• 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 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 legs are long, the hind pair well adapted for jumping: a flea can jump vertically up to 7 inches (18 cm) and horizontally up to 13 inches (33 cm).^[2] This is around 200 times their own body length, making the flea one of the best jumpers of all known animals (relative to body size), second only to the froghopper. 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 clothing). The flea body is hard, polished, and covered with many hairs and short spines directed backward,^[3] which also assist its movements on the host. The tough body is able to withstand great pressure, likely an adaptation to survive attempts to eliminate them by mashing or scratching. Even hard squeezing between the fingers is normally insufficient to kill a flea. It is possible to eliminate them by pressing individual fleas with adhesive tape or softened beeswax (or "cheese" wax) or by rolling a flea briskly between the fingers to disable it then crushing it between the fingernails. Fleas also can be drowned in water and may not survive direct contact with anti-flea pesticides.

Hooke's drawing of a flea in Micrographia

Fleas lay tiny white oval-shaped eggs better viewed through a loupe. The larva is small, pale, has bristles covering its worm-like body, lacks eyes, and has mouthparts adapted to chewing. The larvae feed on various organic matter, especially the feces of mature fleas. The adult flea's diet consists solely of fresh blood.^[4] In the pupal phase, the larva is enclosed in a silken, debris-covered cocoon.

Life cycle and habitat

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.^[3] Eggs are laid in batches of up to 20 or so, usually on the host itself, which means that the eggs can easily roll onto the ground. Because of this, 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.^[2]

Micrograph of a flea larva.

Fleas pass through a complete life cycle consisting of egg, larva, pupa and adult. A typical flea population consists of 50% eggs, 35% larvae, 10% pupae and 5% adults. Completion of the life cycle from egg to adult varies from two weeks to eight months depending on the temperature, humidity, food, and species. Normally after a blood meal, the female flea lays about 45 to 50 eggs per day up to 600 in a lifetime usually on the host (dogs, cats, rats, rabbits, mice, squirrels, chipmunks, raccoons, opossums, foxes, chickens, humans, etc.). Eggs loosely laid in the hair coat, drop out most anywhere especially where the host rests, sleeps or nests (rugs, carpets, upholstered furniture, cat or dog boxes, kennels, sand boxes, etc.). Eggs hatch in two days to two weeks into larvae found indoors in floor cracks & crevices, along baseboards, under rug edges and in furniture or beds. Outdoor development occurs in sandy gravel soils (moist sand boxes, dirt crawlspace under the house, under shrubs, etc.) where the pet may rest or sleep. Sand and gravel are very suitable for larval development which is the reason fleas are erroneously called "sand fleas."

Larvae are blind, avoid light, pass through three larval instars and take a week to several months to develop. Their food consists of digested blood from adult flea feces, dead skin, hair, feathers, and other organic debris. (Larvae do not suck blood.) Pupa mature to adulthood within a silken cocoon woven by the larva to which pet hair, carpet fiber, dust, grass cuttings, and other debris adheres. In about five to fourteen days, adult fleas emerge or may remain resting in the cocoon until the detection of vibration (pet and people movement), pressure (host animal lying down on them), heat, noise, or carbon dioxide (meaning a potential blood source is near). Most fleas overwinter in the larval or pupal stage with survival and growth best during warm, moist winters and spring.

Adult fleas cannot survive or lay eggs without a blood meal, but may live for one year without feeding. There is often a desperate need for flea control after a family has returned from a long vacation. The house has been empty with no cat or dog around for fleas to feed on. When the family and pets are gone, flea eggs hatch and larvae pupate. The adult fleas fully developed inside the pupal cocoon remains in a kind of "limbo" for a long time until a blood source is near. The family returning from vacation is immediately attacked by waiting hungry hordes of fleas. (In just 30 days, 10 female fleas under ideal conditions can multiply to over a quarter million different life stages.)

Newly emerged adult fleas live only about one week if a blood meal is not obtained. However, completely developed adult fleas can live for several months without eating, so long as they do not emerge from their puparia. Optimum temperatures for the flea's life cycle are 70°F to 85°F and optimum humidity is 70%.

^[5]

Classification

Cat flea

Fleas are related to mecoptera,^[6] 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.^[6] 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.

• 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
    • 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

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.

Direct effects of bites

Fleas (Parasite) are not only a nuisance to humans and their pets, but can cause medical problems including flea allergy dermatitis (FAD), secondary skin irritations and, in extreme cases, anemia, tapeworms, stomach flu. Fleas can transmit murine typhus (endemic typhus) fever among animals and from animal to humans. Also, fleas can transmit bubonic plague and any other disease from human to rodent and from rodent to humans. Tapeworms normally infest in humans in severe cases. Although bites are rarely felt, it is the resulting irritation caused by the flea salivary secretions that varies among individuals. Some may witness a severe reaction (general rash or inflammation) resulting in secondary infections caused by scratching the irritated skin area. Others may show no reaction or irritation acquired after repeated bites over several weeks or months. Most bites usually found on the ankles and legs may cause irritation or pain lasting a few minutes, hours or days depending on one's sensitivity. The typical reaction to the bite is the formation of a small, hard, red, slightly-raised (swollen) itching spot. There is a single puncture point in the center of each spot. (Ants and spiders leave two marks when they bite. Mosquitoes, bees, wasps and bedbugs cause a large swelling or welt).^[7]:126

As a vector

Besides the problems posed by the creature itself, fleas can also act as a vector for disease. Fleas transmit not only a variety of viral, bacterial and rickettsial diseases to humans and other animals, but also protozoans and helminths.^[8]:72–73

• bacteria: Murine or endemic typhus.^[7]:124 Fleas have helped cause epidemics by transmitting diseases such as the bubonic plague between rodents and humans by carrying Yersinia pestis bacteria.^[9] Fleas can transmit Yersinia pestis, Rickettsia typhi, Rickettsia felis, and Bartonella henselae.
• virus: myxomatosis.^[8]:73
• helminth: infestation of Hymenolepiasis tapeworm.^[10]
• protozoa: Trypanosome protozoans such as those of the subgenus Herpetosoma, use a variety of flea species opportunistically as vectors.^[8]:74

Fleas that specialize as parasites on specific mammals may use other mammals as hosts; therefore humans are susceptible to the predation of more than one species of flea.^[11]

Flea treatments

For humans

Fleas can become settled in a persons hair in less than ten minutes and cause soreness and itching. The itching associated with flea bites can be treated with anti-itch creams, usually antihistamines or hydrocortisone.^[12] Calamine lotion has been shown to be effective for itching.^[13]

For pets

Flea and tick repellant powder being applied to a dog

Modern flea control is approached using Integrated Pest Management (IPM) protocols at the host (pet) level. IPM is achieved by targeting fleas during 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. Flea adults, larvae, or 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 because many of them, especially the acetylcholinesterase inhibitors, also affect mammals. Popular brands of topical medicines 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. Cedar oil is being used to treat sand-flea infestation of US Military forces in the Gulf.^[14]

Since more than three quarters of a flea's life is spent somewhere other than on the host animal, it is not adequate to treat only the host; it is important also to treat the host's environment. Thorough vacuuming, washing linens in hot water, and treating all hosts in the immediate environment (the entire household, for example) are essential.^[15]

Contemporary commercial products for the topical treatment of flea infestations on pets contain pesticides such as imidacloprid, permethrin, and (S)-methoprene. All flea control products are recommended to be used at least half a year because the lifecycle of flea and tick can last to up to 6 months, and by using one of the flea and tick control products for so long, the infestation is highly prevented and, in the end, stopped. Although all these products are effective in fighting against flea and tick infestations, they have different active ingredients and, because cats cannot metabolize some of the compounds of the product, care must be taken in their use.

For the home

Combating a flea infestation in the home takes patience because for every flea found on an animal, there could be many more developing in the home. A spot-on insecticide 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.

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 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. However, diatomaceous earth is at least potentially dangerous to pets and people when inhaled, so care in use is recommended.

Dried pennyroyal has been suggested as a natural flea control,^[16] but is not recommended in homes with pets due to its high toxicity to mammals.^[17]

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.^[18]

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% to hatch, and larvae need at least 50% humidity to survive. In humid areas, about 20% of the eggs survive to adulthood; in arid areas, less than 5% complete the cycle.^[19] 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% 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

• Pulicosis (Flea bites)
• Anti-itch drug
• Bubonic plague
• Cat flea
• Echidnophaga gallinacea
• Use of DNA in forensic entomology

References

External links

• Flea at the Open Directory Project
• Flea information highlighting habits, habitat, threats and prevention tips
• Integrated Flea Control from University of Nebraska-Lincoln Extension in Lancaster County
• 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)
• 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
• Flea Treatment News from the Flea Control Secrets Blog
• How to Get Rid of Fleas Naturally - a wiki article on getting rid of fleas.
• Flea Control Guide - a guide to how to get rid of fleas.