Housefly

Housefly
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Diptera
Section:	Schizophora
Family:	Muscidae
Genus:	Musca
Species:	M. domestica
Binomial name
Musca domestica Linnaeus, 1758
Subspecies
M. d. calleva Walker, 1849 M. d. domestica Linnaeus, 1758

The housefly (also house fly, house-fly or common housefly), Musca domestica, is a fly of the Brachycera suborder. It is the most common of all domestic flies, accounting for about 90% of all flies in human habitations, and indeed one of the most widely distributed insects, found all over the world; it is considered a pest that can carry serious diseases.

Physical description

A scan of a house fly taken at 40 magnifications under a scanning electron microscope.

Anatomy of a housefly

The adults are 8–12 mm long. Their thorax is gray, with four longitudinal dark lines on the back. The whole body is covered with hair-like projections. The females are slightly larger than the males, and have a much larger space between their red compound eyes. The mass of pupae can range from about 8 to 20 mg under different conditions.^[1]

Like other Diptera (meaning "two-winged"), houseflies have only one pair of wings; the hind pair is reduced to small halteres that aid in flight stability. Characteristically, the media vein (M1+2 or fourth long vein of the wing) shows a sharp upward bend.

Species that appear similar to the housefly include:

• The lesser house fly, Fannia canicularis, is somewhat smaller, more slender, and the media vein is straight.
• The stable fly, Stomoxys calcitrans, has piercing mouthparts and the media vein is only slightly curved.

Life cycle

Each female fly can lay approximately 500 eggs in several batches of about 75 to 150 ^[2]. The eggs are white and are about 1.2 mm in length. Within a day, larvae (maggots) hatch from the eggs; they live and feed in (usually dead and decaying) organic material, such as garbage or feces. They are pale-whitish, 3–9 mm long, thinner at the mouth end, and have no legs. They live at least one week. At the end of their third instar, the maggots crawl to a dry cool place and transform into pupae, colored reddish or brown and about 8 mm long. The adult flies then emerge from the pupae. (This whole cycle is known as complete metamorphosis.) The adults live from two weeks to a month in the wild, or longer in benign laboratory conditions. After having emerged from the pupae, the flies cease to grow; small flies are not young flies, but are instead the result of getting insufficient food during the larval stage.^[3]

The male mounts the female from behind

Some 36 hours after having emerged from the pupa, the female is receptive for mating. The male mounts her from behind to inject sperm. Copulation takes between a few seconds to a couple of minutes.^[3] Normally the female mates only once, storing the sperm to use it repeatedly for laying several sets of eggs.

Housefly pupae killed by parasitic wasp larvae. Each pupa has one hole through which a single adult wasp emerged; feeding occurs during the wasp's larva stage.

Illustration of a housefly

The flies depend on warm temperatures; generally, the warmer the temperature the faster the flies will develop. In winter, most of them survive in the larval or the pupa stage in some protected warm location.^[3]

Diet

Houseflies feed on feces, open sores, sputum, and moist decaying organic matter such as spoiled food, eggs and flesh.^[4] Houseflies can take in only liquid foods. They spit out saliva on solid foods to predigest it, and then suck it back in. They also regurgitate partly digested matter and pass it again to the abdomen.

Sex determination

The housefly is an object of biological research, mainly because of one remarkable quality: the sex determination mechanism. Although a wide variety of sex determination mechanisms exist in nature (e.g. male and female heterogamy, haplodiploidy, environmental factors) the way sex is determined is usually fixed within one species. However, the housefly exhibits many different mechanisms for sex determination, such as male heterogamy (like most insects and mammals), female heterogamy (like birds) and maternal control over offspring sex. This makes the housefly one of the most suitable species to study the evolution of sex determination.^[5]

Evolution

Even though the order of flies (Diptera) is much older, true houseflies are believed to have evolved in the beginning of the Cenozoic era, some 65 million years ago.^[6] They are thought to have originated in the southern Palearctic region, particularly the Middle East. Because of their close, commensal relationship with man, they probably owe their worldwide dispersal to co-migration with humans.^[3]

Flies and humans

In colder climates, houseflies survive only with humans. They have a tendency to aggregate and are difficult to dispel. They are capable of carrying over 100 pathogens, such as typhoid, cholera, Salmonella, bacillary dysentery, tuberculosis, anthrax, ophthalmia, and parasitic worms. The flies in poorer and lower-hygienic areas usually carry more pathogens. Some strains have become immune to most common insecticides.

Close-up of a fly's head, showing compound eyes and hair

House flies feed on liquid or semi-liquid substances beside solid material which has been softened by saliva or vomit. Because of their high intake of food, they deposit feces constantly, one of the factors that makes the insect a dangerous carrier of pathogens. Although they are domestic flies, usually confined to the human habitations, they can fly for several miles from the breeding place. They are active only in daytime and rest at night e.g. at the corners of rooms, ceiling hangings, etc.

Housefly as a vector of disease

Mechanical transmission of organisms on its hairs, mouthparts, vomitus and feces:

• parasitic diseases: cysts of protozoa e.g. Entamoeba histolytica, Giardia lamblia and eggs of helminths e.g.: Ascaris lumbricoides, Trichuros trichura, Haemenolypes nana, Enterobius vermicularis.
• bacterial diseases: typhoid, cholera, dysentery, pyogenic cocci, etc. House flies have been demonstrated to be vectors of Campylobacter and E. coli O157:H7 using PCR ^[7]. House flies can be monitored for bacterial pathogens using filter paper spot cards and PCR ^[8]
• Viruses: enteroviruses: poliomyelitis, viral hepatitis (A & E)..etc.

As a causative agent of diseases

Accidental myiasis

References

External links

• house fly on the UF / IFAS Featured Creatures Web site
• Many annotated images
• Pictorial presentation of life-cycle
• The House Fly and How to Suppress It, by L. O. Howard and F. C. Bishopp. U. S. Department of Agriculture Bulletin No. 1408, 1928, from Project Gutenberg. Also see:
  • Stockbridge, Frank Parker (April 1912). "How To Get Rid Of Flies: The Way They "Swat" Them In Topeka And Order Out The Boy Scouts To Slaughter Them". The World's Work: A History of Our Time XXIII: 692–701. 
  • Page (editor), Walter Hines (June 1912). "How To Make A Flyless Town". The World's Work: A History of Our Time XXIV: 176–179. 
• Video: Common Housefly 60x enlarged and alive under microscope.