On the fly

(invertebrate zoology) The common name for a number of species of the insect order Diptera characterized by a single pair of wings, antennae, compound eyes, and hindwings modified to form knoblike balancing organs, the halters.
(mechanical engineering) A fan with two or more blades used in timepieces or light machinery to govern speed by air resistance.

A member of the insect order Diptera. Insects of other orders are popularly called flies; mayflies, stoneflies, dragonflies, dobsonflies, and caddis flies all have four wings and therefore are not true flies. Mosquitoes, gnats, and midges all have two wings and are therefore also true flies, order Diptera. Hindwings of all Diptera are greatly reduced balancing organs called halteres.

Flies are a numerous and diverse lot, with over 85,000 described species worldwide. North America has 16,000 species belonging to 107 families. Flies are old, their fossils dating from the Triassic, over 200,000,000 years ago.

The flies of greatest importance to humanity are those that suck blood from people or domestic animals. Females of many mosquitoes, deerflies, horseflies, blackflies, and gnats require a meal of blood before producing eggs. When biting, they may introduce pathogenic microorganisms. Mosquitoes may transmit malaria, yellow fever, viral encephalitis, or parasitic roundworms. Tropical blackflies transmit onchocerciasis (river blindness), and sandflies transmit leishmaniasis, a debilitating protozoan infection. Tsetse flies, in which both sexes bite, transmit African sleeping sickness.

Some flies that do not bite may become a nuisance because of their sheer numbers and association with human habitations. The ubiquitous housefly is bothersome and, in unsanitary situations, may contaminate food with the pathogens of hepatitis, polio, cholera, typhoid, or tuberculosis.

Many thousands of flies are predatory, and they doubtless help to suppress populations of insect pests. Especially important are larvae of the family Syrphidae that eat up to 50 aphids per day. Scavenging Diptera are quite important in aiding the quick breakdown of dead animals and plants. See also Diptera; Entomology, economic.

In a hurry, on the run, as in I picked up some groceries on the fly. The transfer of this expression, which literally means "in midair or in flight," dates from the mid-1800s.

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Look up on the fly in Wiktionary, the free dictionary.

Contents 1 Colloquial usage 2 Automotive usage 3 Sports usage 4 Computer usage 5 References

Colloquial usage

In colloquial use, on the fly means something created when needed. The phrase is used to mean:

1. something that was not planned ahead
2. changes that are made during the execution of some activity: ex tempore, impromptu.

Automotive usage

In reference to four-wheel drive vehicles, this term refers to the ability to change from two to four-wheel drive while the car is in gear and moving.^[1]

Sports usage

In ice hockey, the majority of line changes occur "on the fly", that is, while play is still ongoing. Players leap over the boards as quickly as possible as their line is substituted in to avoid any prolonged shifts and to ensure that fresh players remain on the ice as often as possible.

Computer usage

A computer can compute results on the fly, or retrieve a previously stored result.

It can mean to make a copy of a removable media (CD-ROM, DVD, etc) directly, without first saving the source on an intermediate medium (a harddisk); for example, copying a CD-ROM from a CD-ROM drive to a CD-Writer drive.^[2]

When used for encrypted data storage, on the fly the data stream is automatically encrypted as it is written and decrypted when read back again, transparently to software. The acronym OTFE is typically used.

On-the-fly programming is the technique of modifying a program without stopping it.^[3]

A similar concept, Hot swapping, refers to on-the-fly replacement of computer hardware.

References

1. ^ Walczak, Jim, 4WD vs 2WD: The Differences Between 4x4 And 4x2, About.com, http://4wheeldrive.about.com/cs/offroadingtips/a/aa021401a.htm, retrieved on 2009-05-04 
2. ^ , http://www.freeotfe.org/, retrieved on 2009-05-04 
3. ^ Wang, G. E.; Cook, Perry (2002-present), On-the-fly Programming, Princeton University, http://on-the-fly.cs.princeton.edu/, retrieved on 2009-05-04] 

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