Flea
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 SEM of a flea
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Tungidae – sticktight and chigoe fleas (chiggers) |
Flea is the common name for any of the small, secondarily wingless and laterally compressed insects belonging to the order Siphonaptera (some authorities use the name Aphaniptera because it is older, but names above family rank do not follow the rules of priority, so most taxonomists use the more familiar name). Fleas thrive in dark and damp (not wet) places and live as hematophagous ecto-parasites of warm blooded animals like birds and mammals, feeding on their blood. Based on genetic and morphological evidences, it is supposed that they are the descendants of the Scorpionfly family Boreidae, which are also flightless. In the past, however, it was commonly believed based on the similarities of the larvae that fleas had evolved from the flies (Diptera).
Note: There is also a genus of foraminiferan Protozoa named Siphonaptera
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 (1.5 to 5 mm long), agile, usually dark coloured (e.g. the cat flea is reddish-brown), wingless insects. Their bodies are oval and laterally compressed, (i.e., flattened side to side) permitting easy movement through the hairs (or feathers etc.) on the host's body. Head and thorax are relatively small compared to the enlarged abdomen. They have short and thick antennae, only a pair of simple eyes or ocelli and piercing and sucking type of mouthparts adapted to feeding on the blood of their hosts.The thorax consists of three pairs of long and stout jointed appendages, among them, the hind pair is specially well adapted for kinetic jumping (vertically up to 18 cm and horizontally 33 cm)[1] - about 200 times their own body length. The abdoment of the parasite is made of ten segments. The flea body is hard, polished, and covered with many hairs and short spines (bristles) directed backward,[2] allowing the flea a smooth passage through the hairs of its host. Its tough body is able to withstand great pressure, it is likely an adaptation to survive scratching etc. Even hard squeezing between the fingers is often insufficient to kill the flea; it may be necessary to crush them between the fingernails.
Life cycle and habitat
Fleas are holometabolous insects, going through all the four stages of life cycle, namely the embryo (egg), larva, pupa and imago (adult). Adult fleas must feed on blood before they can become capable of reproduction.[2] Thus, after blood meal, breeding starts. Female begins laying in total about 300 to 400 tiny white oval eggs soon after copulation. 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[1] depending on temperature and humidity.
Flea larvae are small cylindrical, maggot like in appearance with neither legs nor eyes. The head is small but equipped with chewing mouthparts, while the body is made of 13 visible and a hidden terminal segments, all provided with rather sparse bristles to aid in crawling. They show negative phototaxis and avoid sunlight, keeping to dark places like sand, cracks and crevices, and bedding. While the adult flea's diet consists solely of blood, their larvae feed on various available organic matter such as dead insects, feces and vegetable matter including the feces of mature fleas.[3] Given an adequate supply of food larvae should pupate within 1-2 weeks. When ready to pupate, the larvae spin little silken cocoons that are viscid, so that particles of sand, dust or lint readily adhere to them. 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.[1] Fleas are known to overwinter or diapause in the larval or pupal stages.
Once the flea reaches adulthood its primary goal is to find blood. Adult fleas only have around a week to find food once they emerge, though they can survive two months to a year between meals. Thus, the life expectancy of adult fleas depends largely on food supply, temperature and humidity. At low temperatures (60° F) well fed fleas may live for several years. In the absence of a host, they have less endurance than ticks or even bugs, as unlike most blood sucking insects, fleas usually feed at frequent intervals, generally at least once a day. A flea population is unevenly distributed, with 50 percent eggs, 35 percent larvae, 10 percent pupae and 5 percent adults.[1] 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[4], 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.[4] 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.
Relationship with host
Fleas attack a wide variety of warm-blooded vertebrates including dogs, 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 parasite 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 self scratching and biting by the animal. In extreme cases, they can lead to anemia.
Besides the problems posed by their sucking of blood, fleas can also act as a vector for many diseases. For example, oriental rat fleas (Xenopsylla cheopsis) is the chief transmitter of the bubonic plague between rodents and humans by carrying its bacteria Yersinia pestis. Murine typhus (endemic typhus) fever caused by Rickettsia typhi, and in some cases tapeworms, Hymenolepis, can also be transmitted by fleas.
Flea treatments
Flea bites can be treated with Calamine lotion or 0.5-1% conc. hydrocortisone cream. Lufenuron is a veterinary medicine that attacks the larval flea's ability to produce chitin. See also Frontline (medicine).
Flea medicines need to be used with care. Phenothrin (85.7%) in combination with Methoprene was a popular topical flea/tick therapy for felines. Phenothrin kills adult fleas and ticks. Methoprene is an insect growth regulator that interrupts the insect's life cycle by killing the eggs. However, the US EPA has pressured at least one manufacturer of products containing these compounds to voluntarily withdraw some products and include strong cautionary statements on others, warning of adverse feline toxicity. The Phenothrin was believed to be the cause of the adverse reactions [5]
A combination of etofenprox (55.0%) and pyriproxyfen (2.2%) is another formulation used in Sergeant's Gold treatment for cats, and possibly others.
Fleas can be controlled in dwellings by application of borax, diatomaceous earth, and other insecticides to floors, furniture and carpeting.
ReferencesISBN links support NWE through referral fees
- ↑ 1.0 1.1 1.2 1.3 Fleas, HYG-2081-97 William F. Lyon, Ohio State University entomology page. Accessed 28 December 2006
- ↑ 2.0 2.1 Fleas - P.G. Koehler and F. M. Oi. Printed July 1993, revised February 2003. Provided by the University of Florida
- ↑ Order Siphonaptera - Fleas - BugGuide.Net Accessed 28 December 2006
- ↑ 4.0 4.1 Grimaldi, D. and Engel, M.S. (2005). Evolution of the Insects. Cambridge University Press. ISBN 0-521-82149-5.
- ↑ EPA: Pesticides - Hartz Flea and Tick Drops for Cats and Kittens to be Phased Out
External links
- {{{2}}} at the Open Directory Project
- 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
- Breaking the Flea Cycle
- How to get rid of fleas
- Sand Flea Bite Picture
- Flea As Weapon
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