Editing Mayfly (section)

== Biology ==

=== Reproduction and life cycle ===

Mayflies are [[hemimetabolous]] (they have "incomplete [[metamorphosis]]"). They are unique among insects in that they moult one more time after acquiring functional wings;<ref name=Lancaster>{{cite book |last1=Lancaster |first1=Jill |last2=Downes |first2=Barbara J. |title=Aquatic Entomology |url=https://books.google.com/books?id=QEYXWiobfcIC&pg=PA10 |year=2013 |publisher=[[Oxford University Press]] |isbn=978-0-19-957322-6 |pages=9–10}}</ref> this last-but-one winged ([[alate]]) instar usually lives a very short time and is known as a subimago, or to fly fishermen as a dun. Mayflies at the subimago stage are a favourite food of many fish, and many [[fishing flies]] are modelled to resemble them. The subimago stage does not survive for long, rarely for more than 24 hours. In some species, it may last for just a few minutes, while the mayflies in the family [[Palingeniidae]] have sexually mature subimagos and no true adult form at all.<ref name=IIBD/>

Often, all the individuals in a population mature at once (a hatch), and for a day or two in the spring or autumn, mayflies are extremely abundant, dancing around each other in large groups, or resting on every available surface.<ref name=McCafferty1983/> In many species the emergence is synchronised with dawn or dusk, and light intensity seems to be an important cue for emergence, but other factors may also be involved. ''[[Baetis intercalaris]]'', for example, usually emerges just after sunset in July and August, but in one year, a large hatch was observed at midday in June. The soft-bodied subimagos are very attractive to predators. Synchronous emergence is probably an [[antipredator adaptation|adaptive strategy]] that reduces the individual's [[Predator satiation|risk of being eaten]].<ref name=Flannagan>{{cite book |last1=Flannagan |first1=John F. |last2=Marshall |first2=K. Eric |title=Advances in Ephemeroptera Biology |url=https://books.google.com/books?id=XQ3pBwAAQBAJ&pg=PA293 |year=2012 |publisher=[[Springer Science+Business Media|Springer Science & Business Media]] |isbn=978-1-4613-3066-0 |page=293 }}</ref> The lifespan of an adult mayfly is very short, varying with the species. The primary function of the adult is reproduction; adults do not feed and have only vestigial [[Insect mouthparts|mouthparts]], while their digestive systems are filled with air.<ref name=Lancaster/> ''[[Dolania americana]]'' has the shortest adult lifespan of any mayfly: the adult females of the species live for less than five minutes.<ref name="entn_Chap">{{cite web |last=Welch |first=Craig H. |title=Chapter 37: Shortest Reproductive Life |work=Book of Insect Records |publisher=[[University of Florida]] |year=1998 |url=http://entnemdept.ifas.ufl.edu/walker/ufbir/chapters/chapter_37.shtml  |archive-url=https://web.archive.org/web/20150730141612/http://entnemdept.ifas.ufl.edu/walker/ufbir/chapters/chapter_37.shtml |archive-date=2015-07-30 }}</ref>

[[File:Shadfly01.jpg|thumb|Mayflies (known locally as shadflies) swarm briefly in enormous numbers in [[Ontario]].]]

Male adults may patrol individually, but most congregate in swarms a few metres above water with clear open sky above it, and perform a nuptial or courtship dance. Each insect has a characteristic up-and-down pattern of movement; strong wingbeats propel it upwards and forwards with the tail sloping down; when it stops moving its wings, it falls passively with the abdomen tilted upwards. Females fly into these swarms, and mating takes place in the air. A rising male clasps the thorax of a female from below using his front legs bent upwards, and inseminates her. Copulation may last just a few seconds, but occasionally a pair remains in tandem and flutters to the ground.<ref name=Spieth>{{cite journal |last=Spieth |first=Herman T. |year=1940 |title=Studies on the biology of the Ephemeroptera. II. The nuptial flight |journal=Journal of the New York Entomological Society |volume=48 |issue=4 |pages=379–390 |jstor=25004879 }}</ref> Males may spend the night in vegetation and return to their dance the following day. Although they do not feed, some briefly touch the surface to drink a little water before flying off.<ref name=Spieth/>

Females typically lay between four hundred and three thousand eggs. The eggs are often dropped onto the surface of the water; sometimes the female deposits them by dipping the tip of her abdomen into the water during flight, releasing a small batch of eggs each time, or deposits them in bulk while standing next to the water. In a few species, the female submerges and places the eggs among plants or in crevices underwater, but in general, they sink to the bottom. The incubation time is variable, depending at least in part on temperature, and may be anything from a few days to nearly a year. Eggs can go into a quiet dormant phase or [[diapause]].<ref>{{cite journal |last=Clifford |first=Hugh F. |journal=Quaestiones Entomologicae| volume=18 |pages=15–90 |year=1982 |title=Life cycles of mayflies (Ephemeroptera), with special reference to voltinism |url=http://www.ephemeroptera-galactica.com/pubs/pub_c/pubcliffordh1982p15.pdf}}</ref> The [[larva]]l growth rate is also temperature-dependent, as is the number of [[ecdysis|moults]]. At anywhere between ten and fifty, these post-embryonic moults are more numerous in mayflies than in most other insect orders. The nymphal stage of mayflies may last from several months to several years, depending on species and environmental conditions.<ref name=Dominguez/>

Around half of all mayfly species whose reproductive biology has been described are [[parthenogenetic]] (able to asexually reproduce), including both partially and exclusively parthenogenetic populations and species.<ref name=":0" />

Many species breed in moving water, where there is a tendency for the eggs and nymphs to get washed downstream. To counteract this, females may fly upriver before depositing their eggs. For example, the female [[Tisza mayfly]], the largest European species with a length of {{convert|12|cm|in|abbr=on}}, flies up to {{convert|3|km|0}} upstream before depositing eggs on the water surface. These sink to the bottom and hatch after 45 days, the nymphs [[burrow]]ing their way into the sediment where they spend two or three years before hatching into subimagos.<ref name=Robinson>{{cite book |last=Robinson |first=William H. |title=Urban Insects and Arachnids: A Handbook of Urban Entomology |url=https://books.google.com/books?id=aluUgDVYJ8wC&pg=PA192 |year=2005 |publisher=[[Cambridge University Press]] |isbn=978-1-139-44347-0 |page=192}}</ref>

When ready to emerge, several different strategies are used. In some species, the transformation of the nymph occurs underwater and the subimago swims to the surface and launches itself into the air.<ref name=McCafferty1983/> In other species, the nymph rises to the surface, bursts out of its skin, remains quiescent for a minute or two resting on the [[exuvia]]e (cast skin) and then flies upwards, and in some, the nymph climbs out of the water before transforming.<ref name=Berner>{{cite book |last1=Berner |first1=Lewis |last2=Pescador |first2=Manuel L. |title=The Mayflies of Florida |url=https://archive.org/details/mayfliesofflorid0000bern |url-access=registration |year=1988 |publisher=[[University Press of Florida]] |isbn=978-0-8130-0845-5 |page=[https://archive.org/details/mayfliesofflorid0000bern/page/108 108] }}</ref>

===Ecology===
[[File: Rainbow trout fish on water surface.jpg|thumb|[[Rainbow trout]] are among the main predators of mayflies.]]

Nymphs live primarily in streams under rocks, in decaying vegetation or in sediments. Few species live in lakes, but they are among the most prolific. For example, the emergence of one species of ''[[Hexagenia]]'' was recorded on [[Doppler weather radar]] by the shoreline of [[Lake Erie]] in 2003.<ref>{{cite web |url=http://www.pserie.psu.edu/seagrant/publications/fs/Mayfly_12-2003.pdf |title=Return of the mayfly: an indicator of an improving habitat |publisher=Pennsylvania Sea Grant |year=2003 |archive-url=https://web.archive.org/web/20070927230149/http://www.pserie.psu.edu/seagrant/publications/fs/Mayfly_12-2003.pdf |archive-date=27 September 2007 |access-date=30 May 2015 }}</ref> In the nymphs of most mayfly species, the paddle-like gills do not function as respiratory surfaces because sufficient oxygen is absorbed through the integument, instead serving to create a respiratory current. However, in low-oxygen environments such as the mud at the bottom of ponds in which ''[[Ephemera vulgata]]'' burrows, the filamentous gills act as true accessory respiratory organs and are used in gaseous exchange.<ref>{{cite journal |last=Wingfield |first=C. A. |year=1939 |title=The function of the gills of mayfly nymphs from different habitats |journal=Journal of Experimental Biology |volume=16 |issue=3 |pages=363–373 |doi=10.1242/jeb.16.3.363 |issn=1477-9145 |url=http://jeb.biologists.org/content/jexbio/16/3/363.full.pdf}}</ref>

In most species, the nymphs are [[herbivore]]s or [[detritivore]]s, feeding on [[algae]], [[diatom]]s or [[detritus]], but in a few species, they are [[predators]] of [[chironomid]] and other small insect larvae and nymphs.<ref>{{cite journal|journal=Aquatic Insects| volume=22 |year=2000| issue= 2| pages=148–159 |title= Guloptiloides: an Extraordinary New Carnivorous Genus of Baetidae (Ephemeroptera) |last1=Gattolliat |first1=Jean-Luc |last2=Sartori |first2=Michel | doi=10.1076/0165-0424(200004)22:2;1-p;ft148| s2cid=86012067 }}</ref><ref>{{cite journal|journal=Aquatic Insects| volume=8| issue=2| year=1986| title= Comparative mouthpart morphology and evolution of the carnivorous heptageniidae (Ephemeroptera) | doi=10.1080/01650428609361236 |last1=McCafferty |first1=W. P. |last2=Provonsha |first2=A. V. | pages=83–89}}</ref> Nymphs of ''[[Povilla]]'' burrow into submerged wood and can be a problem for boat owners in Asia.<ref name=thorpcovich>{{cite book|title=Thorp and Covich's Freshwater Invertebrates|edition=4th| editor=Thorp| editor2=Rogers|year=2014| publisher=[[Academic Press]] |chapter=Order Ephemeroptera| author1=Sartori, Michel| author2=Brittain, John E.|pages=873–891}}</ref> Some are able to shift from one feeding group to another as they grow, thus enabling them to utilise a variety of food resources. They process a great quantity of organic matter as nymphs and transfer a lot of phosphates and nitrates to terrestrial environments when they emerge from the water, thus helping to remove pollutants from aqueous systems.<ref name=Dominguez/> Along with [[caddisfly]] larvae and [[gastropoda|gastropod molluscs]], the grazing of mayfly nymphs has a significant impact on the [[primary producers]], the plants and algae, on the bed of streams and rivers.<ref name=Hauer>{{cite book |last1=Hauer |first1=F. Richard |last2=Lamberti |first2=Gary A.|title=Methods in Stream Ecology |url=https://books.google.com/books?id=rlclsSCF_dQC&pg=PA538 |year=2011 |publisher=[[Academic Press]] |isbn=978-0-08-054743-5 |pages=538, 561}}</ref>

The nymphs are eaten by a wide range of predators and form an important part of the aquatic [[food chain]]. Fish are among the main predators, picking nymphs off the bottom or ingesting them in the water column, and feeding on emerging nymphs and adults on the water surface. Carnivorous [[stonefly]], [[caddisfly]], [[alderfly]] and [[dragonfly]] larvae feed on bottom-dwelling mayfly nymphs, as do aquatic beetles, leeches, crayfish and [[amphibian]]s.<ref name="ThorpRogers2014">{{cite book |last1=Thorp |first1=James H. |last2=Rogers |first2=D. Christopher |title=Thorp and Covich's Freshwater Invertebrates: Ecology and General Biology |url=https://books.google.com/books?id=LB-OAwAAQBAJ&pg=PA886|date=6 September 2014 |publisher=[[Elsevier]] |isbn=978-0-12-385027-0 |page=886}}</ref> Besides the direct mortality caused by these predators, the behaviour of their potential prey is also affected, with the nymphs' growth rate being slowed by the need to hide rather than feed.<ref name=Hauer/> The nymphs are highly susceptible to [[Water pollution|pollution]] and can be useful in the [[biomonitoring]] of water bodies.<ref name=McCafferty1983/> Once they have emerged, large numbers are preyed on by birds, bats and by other insects, such as ''[[Rhamphomyia longicauda]]''.<ref name=Dominguez/>

Mayfly nymphs may serve as [[Host (biology)|hosts]] for [[parasite]]s such as [[nematode]]s and [[trematodes]]. Some of these affect the nymphs' behaviour in such a way that they become more likely to be predated.<ref>{{cite journal |last1=Vance |first1=Sarah A. |last2=Peckarsky |first2=Barbara L. |year=1997 |title=The effect of mermithid parasitism on predation of nymphal ''Baetis bicaudatus'' (Ephemeroptera) by invertebrates |journal=Oecologia |volume=110 |issue=1 |pages=147–152 |doi=10.1007/s004420050143 |pmid=28307463 |bibcode=1997Oecol.110..147V |s2cid=1164123 }}</ref><ref>{{cite journal |last1=Williams |first1=J. K. |last2=Townsend |first2=C. R. |last3=Poulin |first3=Robert |author3-link=Robert Poulin |year=2001 |title=Mermithid nematode infections and drift in the mayfly ''Deleatidium'' spp. (Ephemeroptera). |journal=Journal of Parasitology |volume=87 |issue=5 |pages=1225–1227 |doi=10.1645/0022-3395(2001)087[1225:MNIADI]2.0.CO;2 |pmid=11695410 |s2cid=24933760 }}</ref> Other nematodes turn adult male mayflies into quasi-females which haunt the edges of streams, enabling the parasites to break their way out into the aqueous environment they need to complete their life cycles.<ref name=Zimmer>{{cite book |last=Zimmer |first=Carl |title=Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures |url=https://books.google.com/books?id=cHe5U83nvwcC&pg=PA84 |year=2003 |publisher=Arrow |isbn=978-0-09-945799-2 |pages=84–86}}</ref> The nymphs can also serve as [[intermediate hosts]] for the horsehair worm ''[[Paragordius varius]]'', which causes its [[definitive host]], a [[grasshopper]], to jump into water and drown.<ref>{{cite book|author1=Goater, Timothy M.|author2=Goater, Cameron P.|author3=Esch, Gerald W.|title=Parasitism: The Diversity and Ecology of Animal Parasites |url=https://books.google.com/books?id=zdtRAgAAQBAJ&pg=PA248 |year=2013 |publisher=[[Cambridge University Press]] |isbn=978-1-107-64961-3 |page=248}}</ref>

==== Effects on ecosystem functioning ====

Mayflies are involved in both [[primary production]] and [[bioturbation]]. A study in laboratory simulated streams revealed that the mayfly genus ''[[Centroptilum]]'' increased the export of [[periphyton]],<ref>{{Cite journal|title = Effects of Three Herbivores on Periphyton Communities in Laboratory Streams|journal = Journal of the North American Benthological Society|date = 1987-06-01|issn = 0887-3593|pages = 92–104|volume = 6|issue = 2|doi = 10.2307/1467219|first1 = Gary A.|last1 = Lamberti|first2 = Linda R.|last2 = Ashkenas|first3 = Stan V.|last3 = Gregory|first4 = Alan D.|last4 = Steinman|jstor = 1467219|s2cid = 54578281}}</ref> thus indirectly affecting primary production positively, which is an essential process for ecosystems. The mayfly can also reallocate and alter the nutrient availability in aquatic habitats through the process of bioturbation. By burrowing in the bottom of lakes and redistributing nutrients, mayflies indirectly regulate phytoplankton and epibenthic primary production.<ref>{{Cite journal |last1 = Bachteram |first1 = André M. |last2 = Mazurek |first2 = Kerry A. |last3 = Ciborowsk |first3 = Jan J. H. |title = Sediment Suspension by Burrowing Mayflies (Hexagenia spp., Ephemeroptera: Ephemeridae)|journal = Journal of Great Lakes Research|date = 2005-01-01|pages = 208–222|volume = 31 |issue=Supplement 2|series = Lake Erie Trophic Status Collaborative Study |doi = 10.1016/S0380-1330(05)70315-4}}</ref> Once burrowing to the bottom of the lake, mayfly nymphs begin to billow their respiratory gills. This motion creates current that carries food particles through the burrow and allows the nymph to filter feed. Other mayfly nymphs possess elaborate filter feeding mechanisms like that of the genus ''[[Isonychia]]''. The nymph have forelegs that contain long bristle-like structures that have two rows of hairs. Interlocking hairs form the filter by which the insect traps food particles. The action of filter feeding has a small impact on water purification but an even larger impact on the convergence of small particulate matter into matter of a more complex form that goes on to benefit consumers later in the food chain.<ref>{{Cite journal |last1=Merritt |first1=Richard W. |last2=Wallace |first2=J. Bruce |date=April 1981 |title=Filter-feeding Insects |journal=Scientific American |volume=244 |issue=4 |pages=132–136, 141–142, 144 |url=http://coweeta.uga.edu/publications/671.pdf |doi=10.1038/scientificamerican0481-132 |bibcode=1981SciAm.244d.132M |access-date=2017-01-08|archive-date=2010-06-12 |archive-url=https://web.archive.org/web/20100612033203/http://coweeta.uga.edu/publications/671.pdf}}</ref>

=== Distribution ===

Mayflies are distributed all over the world in clean freshwater habitats,<ref name=NC/> though absent from Antarctica.<ref name="Riffenburgh2007">{{cite book |last=Riffenburgh |first=Beau |title=Encyclopedia of the Antarctic |url=https://books.google.com/books?id=fRJtB2MNdJMC&pg=PA531 |year=2007 |publisher=[[Taylor & Francis]] |isbn=978-0-415-97024-2 |page=531}}</ref> They tend to be absent from oceanic islands or represented by one or two species that have dispersed from nearby mainland. Female mayflies may be dispersed by wind, and eggs may be transferred by adhesion to the legs of waterbirds.<ref>{{cite journal |last=Edmunds Jr. |first=George F. |title= Biogeography and Evolution of Ephemeroptera | journal= Annual Review of Entomology | volume=17 | pages= 21–42 |year=1972| doi=10.1146/annurev.en.17.010172.000321 }}</ref> The greatest generic diversity is found in the [[Neotropical realm]], while the [[Holarctic]] has a smaller number of genera but a high degree of speciation. Some thirteen families are restricted to a single [[bioregion]].<ref>{{cite book |last1=Barber-James |first1=Helen M. |last2=Gattolliat |first2=Jean-Luc |last3=Sartori |first3=Michel |last4=Hubbard |first4=Michael D. |title=Freshwater Animal Diversity Assessment |chapter=Global diversity of mayflies (Ephemeroptera, Insecta) in freshwater |series=Developments in Hydrobiology |year=2008 |volume=198 |pages=339–350 |doi=10.1007/978-1-4020-8259-7_37 |isbn=978-1-4020-8258-0 }}</ref> The main families have some general habitat preferences: the [[Baetidae]] favour warm water; the [[Heptageniidae]] live under stones and prefer fast-flowing water; and the relatively large [[Ephemeridae]] make burrows in sandy lake or river beds.<ref name=NC>{{cite web |title=Ephemeroptera |url=https://projects.ncsu.edu/cals/course/ent425/library/compendium/ephemeroptera.html |website=General Entomology |publisher=[[University of North Carolina]] |access-date=10 July 2015 |archive-date=9 January 2017 |archive-url=https://web.archive.org/web/20170109022807/https://projects.ncsu.edu/cals/course/ent425/library/compendium/ephemeroptera.html  }}</ref>