FLEA

Flea (Ctenocephalides) any member of the insect order Siphonaptera. They are parasites that live on the exterior of the host (i.e., are ectoparasitic). Fleas (see photograph) are bloodsucking insects, important carriers of disease, and sometimes serious pests. As the chief agent transmitting the Black Death (bubonic plague) in the Middle Ages, they were an essential link in the chain of events that killed a quarter of the population of Europe. Flea (Ctenocephalides) a member of one of 1,600 species and subspecies of small, wingless, blood-sucking insects of the order Siphonaptera. The order is divided into three superfamilies. Fleas are found from the Arctic Circle to the Arabian deserts. Specialized anatomical structures allow the flea to attach itself to the skin of mammals or birds and consume their blood. In the process of moving from host to host, fleas may transmit a number of serious human and animal diseases. The adult flea varies in length from 1 to 10 millimetres (0.04 to 0.4 inch) and lives from a few weeks to more than a year. Powerful leg muscles enable fleas to jump distances up to 200 times their body length, developing an acceleration of more than 200 gravities. (This great strength allows fleas to pull miniature carts and perform other stunts in flea circuses.) Although a detailed life cycle is known for only a few species, in general it is known to consist of four stages. The female flea deposits small white eggs on the host's body or in its nest or other habitat. From these eggs very small, legless larvae emerge. In the larval stage the flea consumes bits of dried excrement or blood, flakes of skin, or a special blood-rich fecal matter provided by its parents. After three, or sometimes two, molts, the larva spins a cocoon and enters the pupal stage. The metamorphosis of pupa to adult occurs in this cocoon over the course of days or months. On emerging from its cocoon, the adult flea seeks a vertebrate host. The anatomical structures that distinguish Siphonaptera from other groups function primarily as aids to its ectoparasitic feeding habits. Its compressed body and backward-projecting spines ensure swift movement through the hair or feathers of its host, while the mouthparts, modified for piercing and sucking, include barbed stylets that facilitate skin penetration and tenacious attachment to host tissue. Some fleas, such as the rabbit fleas and the shrew fleas, infest only one particular host species, while others are at home on a wide range of hosts. Ctenocephalides felis, the cat flea, feeds on cats, dogs, foxes, civets, mongooses, opposums, and, when these species are not available, even on humans. Related mammals, even if geographically separated, are often parasitized by closely related flea species. The most heavily afflicted mammalian group is the rodents, including rats, mice, and squirrels, while horses and most other ungulates, monkeys, and apes are largely free of flea infestation. The European rabbit flea (Spilopsyllus cuniculi) has been discovered to exhibit a life cycle closely matched to the hormonal cycles of its host. The Siphonaptera are believed to be descended from an ancestor of the Mecoptera, an order of primitive carnivorous insects that includes the scorpionflies. A fossil flea found in Australia has been claimed to be 200,000,000 years old. The known fossil fleas do not differ significantly from modern fleas. The consequences of flea infestation are of considerable medical and economic importance. The ectoparasitic action of fleas can cause severe inflammation and itching and, in heavy infestation of animals, can lead to serious damage or death through loss of blood. More important than these parasitic effects is the role of fleas as carriers of human and animal diseases. As the principal transmission agent of bubonic plague, the Oriental rat flea (Xenopsylla cheopis) and related species were instrumental in the epidemics that caused the death of a fourth of Europe's population in the Middle Ages. As plague-infected rats succumb to the disease, their contaminated parasites seek fresh hosts, which in crowded conditions may include humans. Occasional cases of plague are still reported in tropical regions, but the disease is well controlled by diagnostic techniques and antibiotics. Murine typhus, a mild fever-producing disease of rodents, is transmitted to humans by Xenopsylla cheopis and other fleas. Fleas are also the carriers of myxomatosis, a viral disease of rabbits, deliberately introduced to rabbit populations in Australia and other areas where the animals have become a serious pest. The transmission of some parasitic worms afflicting dogs and cats involves fleas. Additional reading G.P. Holland, The Siphonaptera of Canada, Tech. Bull. Dep. Agric. Can. 70 (1949), the best work on identification, affinities and host relations of relevant North American fauna; Evolution, Classification and Host-Relations of Siphonaptera, A. Rev. Ent., 9:123146 (1964), a critical review of the literature; G.H.E. Hopkins and M. Rothschild, An Illustrated Catalogue of the Rothschild Collection of Fleas (Siphonaptera) in the British Museum (Natural History), 5 vol. (195371), indispensable for global identification and general morphology of families treated to date; W.L. Jellison, Fleas and Disease, A. Rev. Ent., 4:389414 (1959), a summary of the medical importance of fleas; P.T. Johnson, A Classification of the Siphonaptera of South America with Descriptions of New Species, Mem. Ent. Soc. Wash., 5:1299 (1957), sole opus on South American fleas, well prepared and well illustrated; M. Rothschild, Fleas, Sci. Am. 213:4453 (Dec. 1965), an account of interesting aspects of the biology and behaviour of fleas; The Rabbit Flea and Hormones, in The Biology of Sex, ed. by A. Allison, pp. 189199 (1967), a review of findings on hormonal interrelationships of the rabbit flea and its host, and with T. Clay, Fleas, Flukes and Cuckoos, 3rd ed. (1957), information on bionomics and habits of bird fleas and other bird parasites; R. Traub, Siphonaptera from Central America and Mexico (1950), includes generic revisions and the first study on comparative anatomy of the aedeagus of fleas; United States Department of Agriculture, FleasHow to Control Them, Leaflet No. 392 (n.d.), one of a series of pamphlets on methods of control; Allan H. Benton, An Atlas of the Fleas of the Eastern United States (1980). The Hon. Miriam Louisa Rothschild Robert Traub