Editing Fly (section)

== Anatomy and morphology ==

{{see also |Morphology of Diptera }}

Flies are adapted for aerial movement and typically have short and streamlined bodies. The first [[tagma (biology)|tagma]] of the fly, the head, bears the eyes, the [[antenna (biology)|antenna]]e, and the [[insect mouthparts|mouthparts]] (the labrum, labium, mandible, and maxilla make up the mouthparts). The second tagma, the [[Thorax (insect anatomy)|thorax]], bears the wings and contains the flight muscles on the second segment, which is greatly enlarged; the first and third segments have been reduced to collar-like structures, and the third segment bears the [[halteres]], which help to balance the insect during flight. The third tagma is the [[Abdomen#Arthropoda|abdomen]] consisting of 11 segments, some of which may be fused, and with the three hindmost segments modified for reproduction.<ref name="Dickinson 1999">{{Cite journal |last=Dickinson |first=Michael H. |date=1999 |title=Haltere–mediated equilibrium reflexes of the fruit fly, Drosophila melanogaster |journal=Philosophical Transactions of the Royal Society of London B: Biological Sciences |volume=354 |issue=1385 |pages=903–916 |doi=10.1098/rstb.1999.0442 |pmc=1692594 |pmid=10382224}}</ref><ref name=Resh/> Some Dipterans are mimics and can only be distinguished from their models by very careful inspection. An example of this is ''[[Spilomyia longicornis]]'', which is a fly but mimics a [[vespid]] wasp.

[[File:Tabanus atratus, U, Face, MD 2013-08-21-16.06.31 ZS PMax (9599360121).jpg|thumb|left|Head of [[Tabanus atratus|a horse-fly]] showing large [[compound eye]]s and stout piercing [[insect mouthparts|mouthparts]]]]
[[File:Tephrochlamys rufiventris (female head) (25234095874).jpg|thumb|left|A head of a fly, showing the two compound eyes and three simple eyes clearly.]]

Flies have a mobile head with a pair of large [[compound eye]]s on the sides of the head, and in most species, three small [[ocelli]] on the top. The compound eyes may be close together or widely separated, and in some instances are divided into a dorsal region and a ventral region, perhaps to assist in swarming behaviour. The antennae are well-developed but variable, being thread-like, feathery or comb-like in the different families. The mouthparts are adapted for piercing and sucking, as in the black flies, mosquitoes and robber flies, and for lapping and sucking as in many other groups.<ref name=Resh/> Female [[horse-flies]] use knife-like mandibles and maxillae to make a cross-shaped incision in the host's skin and then lap up the blood that flows. The gut includes large [[Diverticulum|diverticulae]], allowing the insect to store small quantities of liquid after a meal.<ref name="IIBD" />

For visual course control, flies' [[optic flow]] field is analyzed by a set of motion-sensitive neurons.<ref name=pmid11943823>{{cite journal |first1=Juergen |last1=Haag |first2=Alexander |last2=Borst |pmid=11943823 |pmc=6757520 |year=2002 |title=Dendro-dendritic interactions between motion-sensitive large-field neurons in the fly |volume=22 |issue=8 |pages=3227–3233 |journal=[[The Journal of Neuroscience]] |doi=10.1523/JNEUROSCI.22-08-03227.2002 }}</ref> A subset of these neurons is thought to be involved in using the optic flow to estimate the parameters of self-motion, such as yaw, roll, and sideward translation.<ref>{{cite book |doi=10.1007/978-3-642-74082-4_18 |chapter=Neural Mechanisms of Visual Course Control in Insects |title=Facets of Vision |year=1989 |last1=Hausen |first1=Klaus |last2=Egelhaaf |first2=Martin |isbn=978-3-642-74084-8 |pages=391–424 |editor1-first=Doekele Gerben |editor1-last=Stavenga |editor2-first=Roger Clayton |editor2-last=Hardie|chapter-url=https://pub.uni-bielefeld.de/record/1774636 }}</ref> Other neurons are thought to be involved in analyzing the content of the visual scene itself, such as separating figures from the ground using motion parallax.<ref>{{cite journal |first1=Martin |last1=Egelhaaf |year=1985 |title=On the neuronal basis of figure-ground discrimination by relative motion in the visual system of the fly |journal=Biological Cybernetics |volume=52 |issue=3 |pages=195–209 |url=https://link.springer.com/article/10.1007%2FBF00339948 |doi=10.1007/BF00339948 |s2cid=227306897 }}</ref><ref>{{cite journal |first1=Bernd |last1=Kimmerle |first2=Martin |last2=Egelhaaf |pmid=10934276 |pmc=6772600 |year=2000 |title=Performance of fly visual interneurons during object fixation |volume=20 |issue=16 |pages=6256–66 |journal=[[The Journal of Neuroscience]] |doi=10.1523/JNEUROSCI.20-16-06256.2000 }}</ref> The [[H1 neuron]] is responsible for detecting horizontal motion across the entire visual field of the fly, allowing the fly to generate and guide stabilizing motor corrections midflight with respect to yaw.<ref name="DoiBFMissing">{{cite journal |doi=10.1007/BF00660179 |title=Functional properties of the H1-neurone in the third optic Ganglion of the Blowfly, ''Phaenicia'' |year=1980 |last1=Eckert |first1=Hendrik |journal=[[Journal of Comparative Physiology]] |volume=135 |issue=1 |pages=29–39|s2cid=26541123 }}</ref> The ocelli are concerned in the detection of changes in light intensity, enabling the fly to react swiftly to the approach of an object.<ref name=Ruppert>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |pages=735–736 }}</ref>

Like other insects, flies have [[chemoreceptor]]s that detect smell and taste, and [[mechanoreceptor]]s that respond to touch. The third segments of the antennae and the maxillary palps bear the main olfactory receptors, while the gustatory receptors are in the labium, pharynx, feet, wing margins and female genitalia,<ref>{{cite journal |last=Stocker |first=Reinhard F. |year=2005 |title=The organization of the chemosensory system in ''Drosophila melanogaster'': a review |journal=Cell and Tissue Research |volume=275 |issue=1 |pages=3–26 |doi=10.1007/BF00305372|pmid=8118845 |s2cid=23210046 }}</ref> enabling flies to taste their food by walking on it. The taste receptors in females at the tip of the abdomen receive information on the suitability of a site for ovipositing.<ref name=Ruppert/> Flies that feed on blood have special sensory structures that can detect [[infrared]] emissions, and use them to home in on their hosts. Many blood-sucking flies can detect the raised concentration of [[carbon dioxide]] that occurs near large animals.<ref>{{cite journal |last1=Zhu |first1=Junwei J. |last2=Zhang |first2=Qing-he |last3=Taylor |first3=David B. |last4=Friesen |first4=Kristina A. |date=2016-09-01 |title=Visual and olfactory enhancement of stable fly trapping |url=http://digitalcommons.unl.edu/usdaarsfacpub/1555 |journal=Pest Management Science |volume=72 |issue=9 |pages=1765–1771 |doi=10.1002/ps.4207|pmid=26662853 }}</ref> Some tachinid flies (Ormiinae) which are parasitoids of [[Tettigoniidae|bush crickets]], have sound receptors to help them locate their singing hosts.<ref>{{cite journal |last1=Lakes-Harlan |first1=Reinhard |author2=Jacobs, Kirsten |author3=Allen, Geoff R. |year=2007 |title=Comparison of auditory sense organs in parasitoid Tachinidae (Diptera) hosted by Tettigoniidae (Orthoptera) and homologous structures in a non-hearing Phoridae (Diptera) |journal=Zoomorphology |volume=126 |issue=4 |pages=229–243 |doi=10.1007/s00435-007-0043-3 |s2cid=46359462 }}</ref>

[[File:Halteres-Tipule.jpg|thumb|A [[crane fly]], showing the hind wings reduced to drumstick-shaped [[haltere]]s]]

Diptera have one pair of fore [[insect wing|wings]] on the [[mesothorax]] and a pair of [[halteres]], or reduced hind wings, on the [[metathorax]]. A further adaptation for flight is the reduction in number of the neural [[ganglia]], and concentration of nerve tissue in the thorax, a feature that is most extreme in the highly derived Muscomorpha infraorder.<ref name=IIBD>{{cite book |last1=Hoell |first1=H. V. |last2=Doyen |first2=J. T. |last3=Purcell |first3=A. H. |year=1998 |title=Introduction to Insect Biology and Diversity |edition=2nd |publisher= Oxford University Press |isbn=978-0-19-510033-4 |pages=493–499}}</ref> Some flies such as the ectoparasitic [[Nycteribiidae]] and [[Streblidae]] are exceptional in having lost their wings and become flightless. The only other order of insects bearing a single pair of true, functional wings, in addition to any form of halteres, are the [[Strepsiptera]]. In contrast to the flies, the Strepsiptera bear their halteres on the mesothorax and their flight wings on the metathorax.<ref>{{cite web |url=http://www.ento.csiro.au/education/insects/strepsiptera.html |title=Strepsiptera: ''Stylops'' |website=Insects and their Allies |publisher=[[CSIRO]] |access-date=25 May 2016}}</ref> Each of the fly's six [[Arthropod leg|legs]] has a typical insect structure of coxa, trochanter, femur, tibia and tarsus, with the tarsus in most instances being subdivided into five [[tarsomere]]s.<ref name=Resh/> At the tip of the limb is a pair of claws, and between these are cushion-like structures known as [[pulvilli]] which provide adhesion.<ref>{{cite journal |last1=Langer |first1=Mattias G. |last2=Ruppersberg |first2=J. Peter |last3=Gorb |first3=Stanislav N. |year=2004 |title=Adhesion Forces Measured at the Level of a Terminal Plate of the Fly's Seta |journal=[[Proceedings of the Royal Society]] B |volume=271 |issue=1554 |pages=2209–2215 |jstor=4142949 |doi=10.1098/rspb.2004.2850 |pmid=15539345 |pmc=1691860}}</ref>

The abdomen shows considerable variability among members of the order. It consists of eleven segments in primitive groups and ten segments in more derived groups, the tenth and eleventh segments having fused.<ref name=Gibb>{{cite book |last1=Gibb |first1=Timothy J. |last2=Oseto |first2=Christian |title=Arthropod Collection and Identification: Laboratory and Field Techniques |url=https://books.google.com/books?id=kyZGPWmILq0C&pg=PA189 |year=2010 |publisher=Academic Press |isbn=978-0-08-091925-6 |page=189}}</ref> The last two or three segments are adapted for reproduction. Each segment is made up of a dorsal and a ventral [[sclerite]], connected by an elastic membrane. In some females, the sclerites are rolled into a flexible, telescopic [[ovipositor]].<ref name=Resh/>

===Flight===

{{Further|Insect flight}}

[[File:March-fly-in-flight.jpg|thumb|[[Horse-fly|Tabanid]] fly in [[Insect flight|flight]]]]

Flies are capable of great manoeuvrability during flight due to the presence of the halteres. These act as [[gyroscopic]] organs and are rapidly oscillated in time with the wings; they act as a balance and guidance system by providing rapid feedback to the wing-steering muscles, and flies deprived of their halteres are unable to fly. The wings and halteres move in synchrony but the amplitude of each wing beat is independent, allowing the fly to turn sideways.<ref name="Sane 2015">{{cite journal |last1=Deora |first1=Tanvi |last2=Singh |first2=Amit Kumar |last3=Sane |first3=Sanjay P. |title=Biomechanical basis of wing and haltere coordination in flies |journal=[[PNAS]] |date=3 February 2015 |volume=112 |issue=5 |pages=1481–1486 |doi=10.1073/pnas.1412279112 |pmid=25605915 |pmc=4321282|bibcode=2015PNAS..112.1481D |doi-access=free }}</ref> The wings of the fly are attached to two kinds of muscles, those used to power it and another set used for fine control.<ref>{{Cite journal |last1=Dickinson |first1=Michael H |last2=Tu |first2=Michael S |date=1997-03-01 |title=The function of dipteran flight muscle |journal=Comparative Biochemistry and Physiology Part A: Physiology |volume=116 |issue=3 |pages=223–238 |doi=10.1016/S0300-9629(96)00162-4}}</ref>

Flies tend to fly in a straight line then make a rapid change in direction before continuing on a different straight path. The directional changes are called [[saccade]]s and typically involve an angle of 90°, being achieved in 50 milliseconds. They are initiated by visual stimuli as the fly observes an object, nerves then activate steering muscles in the thorax that cause a small change in wing stroke which generate sufficient torque to turn. Detecting this within four or five wingbeats, the halteres trigger a counter-turn and the fly heads off in a new direction.<ref>{{cite journal |last=Dickinson |first=Michael H. |year=2005 |title=The initiation and control of rapid flight manoeuvres in fruit flies |journal=Integrative and Comparative Biology |volume=45 |issue=2 |pages=274–281 |doi=10.1093/icb/45.2.274 |pmid=21676771 |s2cid=7306151 |doi-access=free }}</ref>

Flies have rapid reflexes that aid their escape from predators but their sustained flight speeds are low. [[Dolichopus pennatus|Dolichopodid]] flies in the genus ''Condylostylus'' respond in less than five milliseconds to camera flashes by taking flight.<ref>{{cite journal |doi=10.1653/024.094.0240 |title=Faster than a flash: The fastest visual startle reflex response is found in a long-legged fly, ''Condylostylus'' sp. (Dolichopodidae) |journal=[[The Florida Entomologist]] |volume=94 |issue=2 |pages=367–369 |year=2011 |last1=Sourakov |first1=Andrei|s2cid=86502767 |doi-access=free }}</ref> In the past, the deer bot fly, ''[[Cephenemyia]]'', was claimed to be one of the fastest insects on the basis of an estimate made visually by [[Charles Henry Tyler Townsend|Charles Townsend]] in 1927.<ref>{{cite journal |title=On the ''Cephenemyia'' mechanism and the Daylight-Day circuit of the Earth by flight |last=Townsend |first=Charles H.T. |journal=Journal of the New York Entomological Society |volume=35 |issue=3 |year=1927 |pages=245–252 |jstor=25004207}}</ref> This claim, of speeds of 600 to 800 miles per hour, was regularly repeated until it was shown to be physically impossible as well as incorrect by Irving Langmuir. Langmuir suggested an estimated speed of 25 miles per hour.<ref>{{cite journal |journal=Science |volume=87 |issue=2254 |pages=233–234 |year=1938 |last=Langmuir |first=Irving |title=The speed of the deer fly |pmid=17770404 | doi=10.1126/science.87.2254.233| bibcode=1938Sci....87..233L }}</ref><ref>{{cite journal |title=Speed of ''Cephenemyia'' |last=Townsend |first=Charles H.T. |journal=Journal of the New York Entomological Society |volume=47 |issue=1 |year=1939 | pages=43–46 |jstor=25004791}}</ref><ref>{{cite journal |doi=10.1093/ae/45.1.4 |title=Getting Up to Speed |journal=American Entomologist |volume=45 |pages=4–5 |year=1999 |last1=Berenbaum |first1=M.|doi-access=free }}</ref>

Although most flies live and fly close to the ground, a few are known to fly at heights and a few like ''Oscinella'' (Chloropidae) are known to be dispersed by winds at altitudes of up to 2,000&nbsp;ft and over long distances.<ref>{{cite journal |title=High altitude migration of ''Oscinella frit'' L. (Diptera: Chloropidae) |last1=Johnson |first1=C.G. |author2=Taylor, L.R. |author3=T.R.E. Southwood |journal=Journal of Animal Ecology |volume=31 |issue=2 |year=1962 |pages=373–383 |jstor=2148 |doi=10.2307/2148}}</ref> Some hover flies like ''Metasyrphus corollae'' have been known to undertake long flights in response to aphid population spurts.<ref>{{cite journal |doi=10.1111/j.1365-2311.1984.tb00856.x |title=Why does the hoverfly ''Metasyrphus corollae'' migrate? |journal=Ecological Entomology |volume=9 |issue=3 |pages=329–335 |year=1984 |last1=Svensson |first1=BO G. |last2=Janzon |first2=Lars-ÅKE|s2cid=83629356 }}</ref>

Males of fly species such as ''[[Cuterebra]]'', many hover flies,<ref>{{cite journal |doi=10.4039/Ent113695-8 |title=Territoriality in the Drone Fly, ''Eristalis tenax'' (Diptera: Syrphidae) |journal=The Canadian Entomologist |volume=113 |issue=8 |pages=695–704 |year=2012 |last1=Wellington |first1=W. G. |last2=Fitzpatrick |first2=Sheila M.|s2cid=86181761 }}</ref> bee flies (Bombyliidae)<ref>{{cite journal |doi=10.1007/BF01052332 |title=The mating system of a bee fly (Diptera: Bombyliidae). II. Factors affecting male territorial and mating success |journal=Journal of Insect Behavior |volume=3 |issue=5 |pages=619–636 |year=1990 |last1=Dodson |first1=Gary |last2=Yeates |first2=David|s2cid=25061334 }}</ref> and fruit flies (Tephritidae)<ref name="ReferenceA">{{cite journal |doi=10.1163/156853909X410766 |title=Territorial contests within and between two species of flies (Diptera: Richardiidae) in the wild |journal=Behaviour |volume=146 |issue=2 |pages=245–262 |year=2009 |last1=Becerril-Morales |first1=Felipe |last2=Macías-Ordóñez |first2=Rogelio}}</ref> maintain territories within which they engage in aerial pursuit to drive away intruding males and other species.<ref>{{cite journal |doi=10.1016/S0003-3472(83)80074-8 |title=Hilltop territoriality in a Sonoran desert bot fly (Diptera: Cuterebridae) |journal=Animal Behaviour |volume=31 |issue=2 |pages=518 |year=1983 |last1=Alcock |first1=John |last2=Schaefer |first2=John E.|s2cid=53180240 }}</ref> While these territories may be held by individual males, some species, such as ''[[Anopheles freeborni|A. freeborni]]'',<ref>{{Cite journal |last1=Yuval |first1=B. |last2=Bouskila |first2=A. |date=1993-03-01 |title=Temporal dynamics of mating and predation in mosquito swarms|journal=Oecologia |volume=95 |issue=1 |pages=65–69 |doi=10.1007/BF00649508 |pmid=28313313|bibcode=1993Oecol..95...65Y |s2cid=22921039}}</ref> form [[lek mating|leks]] with many males aggregating in displays.<ref name="ReferenceA"/> Some flies maintain an airspace and still others form dense swarms that maintain a stationary location with respect to landmarks. Many flies mate in flight while swarming.<ref>{{cite journal |doi=10.1146/annurev.en.14.010169.001415 |title=The swarming and mating flight of Diptera |journal=Annual Review of Entomology |volume=14 |pages=271–298 |year=1969 |last1=Downes |first1=J. A.}}</ref>