Editing Fly (section)

== Life cycle and development ==

{{see also |Biology of Diptera}}

[[File:Anthomyiidae sp. 1 (aka).jpg|thumb|Mating [[Anthomyiidae|anthomyiid flies]]]]

Diptera go through a complete metamorphosis with four distinct life stages – egg, larva, pupa and adult.

=== Larva ===

In many flies, the larval stage is long and adults may have a short life. Most dipteran larvae develop in protected environments; many are aquatic and others are found in moist places such as carrion, fruit, vegetable matter, fungi and, in the case of parasitic species, inside their hosts. They tend to have thin cuticles and become desiccated if exposed to the air. Apart from the [[Brachycera]], most dipteran larvae have sclerotised head capsules, which may be reduced to remnant mouth hooks; the Brachycera, however, have soft, gelatinized head capsules from which the sclerites are reduced or missing. Many of these larvae retract their heads into their thorax.<ref name=Resh/><ref name=Gullan/> The [[Spiracle (arthropods)|spiracles]] in the larva and pupa do not have any internal mechanical closing device.<ref>[https://esc-sec.ca/wp/wp-content/uploads/2017/03/AAFC_manual_of_nearctic_diptera_vol_1.pdf Manual of Nearctic Diptera]</ref>

[[File:Stomoxys-stable-fly-life-cycle-2.jpg|thumb|left|Life cycle of stable fly ''[[Stomoxys calcitrans]]'', showing eggs, 3 [[larva]]l [[instar]]s, [[pupa]], and adult]]

Some other anatomical distinction exists between the larvae of the [[Nematocera]] and the [[Brachycera]]. Especially in the Brachycera, little demarcation is seen between the thorax and abdomen, though the demarcation may be visible in many Nematocera, such as mosquitoes; in the Brachycera, the head of the larva is not clearly distinguishable from the rest of the body, and few, if any, sclerites are present. Informally, such brachyceran larvae are called maggots,<ref name="isbn0-19-861271-0">{{cite book |last=Brown |first=Lesley |title=The New shorter Oxford English dictionary on historical principles |publisher=Clarendon |year=1993 |isbn=978-0-19-861271-1 |url-access=registration |url=https://archive.org/details/newshorteroxford00lesl }}</ref> but the term is not technical and often applied indifferently to fly larvae or insect larvae in general. The eyes and antennae of brachyceran larvae are reduced or absent, and the abdomen also lacks appendages such as [[cercus|cerci]]. This lack of features is an adaptation to food such as carrion, decaying detritus, or host tissues surrounding [[endoparasites]].<ref name="IIBD" /> Nematoceran larvae generally have well-developed eyes and antennae, while those of Brachyceran larvae are reduced or modified.<ref name=Lancaster>{{cite book |last1=Lancaster |first1=Jill |last2=Downes |first2=Barbara J. |title=Aquatic Entomology |url=https://books.google.com/books?id=jNAUDAAAQBAJ&pg=PA16 |year=2013 |publisher=Oxford University Press |isbn=978-0-19-957321-9 |page=16}}</ref>

Dipteran larvae have no jointed, "true legs",<ref name=Gullan>{{cite book |last1=Gullan |first1=P.J. |last2=Cranston |first2=P.S. |title=The Insects: An Outline of Entomology 3rd Edition |publisher=John Wiley & Sons |isbn=978-1-4051-4457-5 |year = 2005 |pages = 499–505}}</ref> but some dipteran larvae, such as species of [[Simuliidae]], [[Tabanidae]] and [[Vermileonidae]], have [[proleg]]s adapted to hold onto a substrate in flowing water, host tissues or prey.<ref>{{cite book |last=Chapman |first=R. F. |title=The Insects; Structure & Function |url=https://archive.org/details/insectsstructure0000chap |url-access=registration |year=1998 |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-57890-5}}</ref> The majority of dipterans are [[oviparous]] and lay batches of eggs, but some species are [[ovoviviparous]], where the larvae starting development inside the eggs before they hatch or viviparous, the larvae hatching and maturing in the body of the mother before being externally deposited. These are found especially in groups that have larvae dependent on food sources that are short-lived or are accessible for brief periods.<ref>{{Cite journal |last1=Meier |first1=Rudolf |last2=Kotrba |first2=Marion |last3=Ferrar |first3=Paul |date=August 1999 |title=Ovoviviparity and viviparity in the Diptera |journal=Biological Reviews |volume=74 |issue=3 |pages=199–258 |doi=10.1111/j.1469-185X.1999.tb00186.x|s2cid=86129322 }}</ref> This is widespread in some families such as the Sarcophagidae. In ''[[Hylemya strigosa]]'' (Anthomyiidae) the larva moults to the second instar before hatching, and in ''[[Termitoxenia]]'' (Phoridae) females have incubation pouches, and a full developed third instar larva is deposited by the adult and it almost immediately pupates with no freely feeding larval stage. The [[tsetse fly]] (as well as other Glossinidae, Hippoboscidae, Nycteribidae and Streblidae) exhibits [[adenotrophic viviparity]]; a single fertilised egg is retained in the oviduct and the developing larva feeds on glandular secretions. When fully grown, the female finds a spot with soft soil and the larva works its way out of the oviduct, buries itself and pupates. Some flies like ''[[Lundstroemia parthenogenetica]]'' (Chironomidae) reproduce by [[thelytokous]] [[parthenogenesis]], and some [[gall midge]]s have larvae that can produce eggs ([[paedogenesis]]).<ref>{{Cite journal |last1=Mcmahon |first1=Dino P. |last2=Hayward |first2=Alexander |date=April 2016 |title=Why grow up? A perspective on insect strategies to avoid metamorphosis |journal=Ecological Entomology |volume=41 |issue=5 |pages=505–515 |doi=10.1111/een.12313|s2cid=86908583 |doi-access=free }}</ref><ref>{{cite book |title=Entomology |last=Gillott |first=Cedric |publisher=Springer |year=2005 |edition=3|pages=614–615}}</ref>

=== Pupa ===

The [[pupa]]e take various forms. In some groups, particularly the Nematocera, the pupa is intermediate between the larval and adult form; these pupae are described as "obtect", having the future appendages visible as structures that adhere to the pupal body. The outer surface of the pupa may be leathery and bear spines, respiratory features or locomotory paddles. In other groups, described as "coarctate", the appendages are not visible. In these, the outer surface is a [[puparium]], formed from the last larval skin, and the actual pupa is concealed within. When the adult insect is ready to emerge from this tough, desiccation-resistant capsule, it inflates [[ptilinum|a balloon-like structure on its head]], and forces its way out.<ref name=Resh/>

=== Adult ===

The adult stage is usually short, its function is only to mate and lay eggs. The genitalia of male flies are rotated to a varying degree from the position found in other insects.<ref>{{Cite web |url=http://psyche.entclub.org/48/48-079.html |title=Crampton, G. The TemporalAbdominal Structures of Male Diptera. |access-date=22 May 2018 |archive-date=23 May 2018 |archive-url=https://web.archive.org/web/20180523095550/http://psyche.entclub.org/48/48-079.html |url-status=dead }}</ref> In some flies, this is a temporary rotation during mating, but in others, it is a permanent torsion of the organs that occurs during the pupal stage. This torsion may lead to the [[anus]] being below the genitals, or, in the case of 360° torsion, to the sperm duct being wrapped around the gut and the external organs being in their usual position. When flies mate, the male initially flies on top of the female, facing in the same direction, but then turns around to face in the opposite direction. This forces the male to lie on his back for his genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright. This leads to flies having more reproduction abilities than most insects, and much quicker. Flies occur in large populations due to their ability to mate effectively and quickly during the mating season.<ref name="IIBD" /> More primitive groups mates in the air during swarming, but most of the more advanced species with a 360° torsion mate on a substrate.<ref>[https://web.archive.org/web/20160413002209/https://www.newscientist.com/article/mg12717314-500-sex-with-a-twist-in-the-tail-the-common-or-garden-housefly/ Sex with a twist in the tail: The common-or-garden housefly]</ref>