Flea

Flea, the common name for the <a href="/facts/Order_(biology)/GKLJvIpt">order</a> Siphonaptera, includes 2,500 species of small flightless <a href="/facts/Insect/IgDNvnUL">insects</a> that live as external <a href="/facts/Parasites/HWPcgky7">parasites</a> of <a href="/facts/Mammal/phSwTzBo">mammals</a> and <a href="/facts/Bird/RJF6zwLP">birds</a>. Fleas live by <a href="/facts/Hematophagy/plcTvPFg">ingesting the blood</a> of their hosts. Adult fleas grow to about 3 millimetres (1⁄8 inch) long, are usually dark in color, and have bodies that are "flattened" sideways or narrow, enabling them to move through their hosts' fur or feathers. They lack wings; their hind legs are extremely well adapted for jumping. Their claws keep them from being dislodged, and their mouthparts are adapted for piercing skin and sucking <a href="/facts/Blood/03zEulkj">blood</a>. Some species can leap 50 times their body length, a feat second only to jumps made by another group of insects, the <a href="/facts/Superfamily_(taxonomy)/bPFQpe9A">superfamily</a> of <a href="/facts/Froghopper/dRMhKxN2">froghoppers</a>. Flea larvae are worm-like, with no limbs; they have chewing mouthparts and feed on organic debris left on their hosts' skin.
Genetic evidence indicates that fleas are a specialised lineage of parasitic <a href="/facts/Scorpionflies/6IScmTuN">scorpionflies</a> (Mecoptera) sensu lato, most closely related to the family <a href="/facts/Nannochoristidae/Cr89tXIt">Nannochoristidae</a>. The earliest known fleas lived in the Middle <a href="/facts/Jurassic/o5Cy4KzX">Jurassic</a>; modern-looking forms appeared in the <a href="/facts/Cenozoic/yFslcz6n">Cenozoic</a>. Fleas probably originated on mammals first and expanded their reach to birds. Each species of flea specializes, more or less, on one species of host: many species of flea never breed on any other host; some are less selective. Some families of fleas are exclusive to a single host group; for example, the Malacopsyllidae are found only on <a href="/facts/Armadillo/4acbwyFn">armadillos</a>, the <a href="/facts/Ischnopsyllidae/Vnf4fR0V">Ischnopsyllidae</a> only on <a href="/facts/Bat/CJudzNt1">bats</a>, and the Chimaeropsyllidae only on <a href="/facts/Elephant_shrew/M7VIfdX6">elephant shrews</a>.
The oriental rat flea, <a href="/facts/Xenopsylla_cheopis/XK8dvE9B">Xenopsylla cheopis</a>, is a <a href="/facts/Vector_(epidemiology)/bepASE2M">vector</a> of <a href="/facts/Yersinia_pestis/LBCfCSeW">Yersinia pestis</a>, the <a href="/facts/Bacterium/wC8xSCsU">bacterium</a> that causes <a href="/facts/Bubonic_plague/N9dCQ3EP">bubonic plague</a>. The disease was spread to humans by rodents, such as the <a href="/facts/Black_rat/tphNVemz">black rat</a>, which were bitten by infected fleas. Major outbreaks included the <a href="/facts/Plague_of_Justinian/srTzssYm">Plague of Justinian</a>, about 540, and the <a href="/facts/Black_Death/fztxlxgl">Black Death</a>, about 1350, each of which killed a sizeable fraction of the world's people.
Fleas appear in human culture in such diverse forms as <a href="/facts/Flea_circus/enT8zYqo">flea circuses</a>; poems, such as <a href="/facts/John_Donne/jLH99Aaw">John Donne</a>'s erotic "<a href="/facts/The_Flea_(poem)/XMmzI7Sz">The Flea</a>"; works of music, such as those by <a href="/facts/Modest_Mussorgsky/pvU2M4o7">Modest Mussorgsky</a>; and a film by <a href="/facts/Charlie_Chaplin/24P6I5lz">Charlie Chaplin</a>.

Flea open-in-new

Flea