Editing Damselfly (section)

== Biology ==
[[File:Blue Damselflies sparkling over Kew pond.webm|thumb|Blue damselflies swarming over pond in [[Kew Gardens]]. Some pairs (blue male in front) are seen.]]
[[File:Damselfly catch Updated.webm|thumb|right|thumbtime=0|[[Ischnura perparva|Western forktail damselfly]] attempting on-the-fly catches. Each repeated in slow motion. The second prey landed, escaping capture. Finally closeup devouring medium sized fly.]]

[[File:Damselfly eating Crane fly.jpg|left|thumb|Damselfly eating a Crane fly]]
Adult damselflies catch and eat flies, mosquitoes, and other small insects. Often they hover among grasses and low vegetation, picking prey off stems and leaves with their spiny legs (unlike dragonflies which prefer catching flying prey).<ref name=Acorn/><ref>[https://books.google.com/books?id=Ygoyg1grhJwC&dq=dragonflies+generally+capture+their+prey+while+in+flight&pg=PA8 Dragonflies and Damselflies of Georgia and the Southeast]</ref> Although predominantly using vision to locate their prey, adults may also make use of olfactory cues.<ref>{{cite journal|title= First evidence of the use of olfaction in Odonata behaviour| journal=Journal of Insect Physiology|volume=62|year=2014|pages=26–31|first1=Silvana|last1=Piersanti|first2= Francesca|last2= Frati|first3=Eric|last3= Conti|first4= Elda|last4=Gaino|first5=Manuela|last5= Rebora|first6= Gianandrea |last6=Salerno|doi=10.1016/j.jinsphys.2014.01.006| pmid=24486162| bibcode=2014JInsP..62...26P}}</ref> No species are known to hunt at night, but some are crepuscular, perhaps taking advantage of newly hatched flies and other aquatic insects at a time when larger dragonflies are roosting.<ref name=Heckman/> In tropical South America, helicopter damselflies ([[Pseudostigmatidae]]) feed on [[spider]]s, hovering near an orb web and plucking the spider, or its entangled prey, from the web.<ref>{{cite journal |author1=Ingley, Spencer J. |author2=Bybee, Seth M. |author3=Tennessen, Kenneth J. |author4=Whiting, Michael F. |author5=Branham, Marc A. |year=2012 |title=Life on the fly: phylogenetics and evolution of the helicopter damselflies (Odonata, Pseudostigmatidae) |journal=Zoologica Scripta |volume=41 |issue=6 |pages=637–650 |doi=10.1111/j.1463-6409.2012.00555.x |s2cid=82370392 }}</ref> There are few pools and lakes in these habitats, and these damselflies breed in temporary water bodies in holes in trees, the rosettes of [[bromeliad]]s and even the hollow stems of [[bamboo]]s.<ref>{{cite conference | last = Fincke | first = Ola M. | title = Use of Forest and Tree Species, and Dispersal by Giant Damselflies (Pseudostigmatidae): Their Prospects in Fragmented Forests | book-title = Fourth WDA International Symposium of Odonatology, Pontevedra (Spain), July 2005 | editor = Adolfo Cordero Rivera | pages = 103–125 | publisher = Pensoft Publishers | year = 2006 | location = Sofia—Moscow | url = http://faculty-staff.ou.edu/F/Ola.M.Fincke-1/06%20-%20Fincke.pdf | url-status = dead | archive-url = https://web.archive.org/web/20070628043336/http://faculty-staff.ou.edu/F/Ola.M.Fincke-1/06%20-%20Fincke.pdf | archive-date = 2007-06-28 }}</ref>

The nymphs of damselflies have been less researched than their dragonfly counterparts, and many have not even been identified. They choose their prey according to size and seem less able to overpower larger prey than can dragonfly nymphs. The major part of the diet of most species appears to be [[crustacean]]s such as [[Cladocera|water fleas]].<ref name=Heckman/>

===Ecology===
[[File:Panorama of Thursley Common, looking over the bog pools.JPG|thumb|upright=1.7<!--size for very low image-->|Fine damselfly habitat: panorama of [[Thursley Common]], looking over the acid bog pools]]
[[File:The damselfly Platycnemis pennipes washing itself.webm|thumb|Damselfly grooming]]
[[File:Pseudagrion decorum damselfly with water mites.jpg|thumb|Water mites parasitizing ''[[Pseudagrion decorum]]'']]

Damselflies exist in a range of habitats in and around the wetlands needed for their larval development; these include open spaces for finding mates, suitable perches, open aspect, roosting sites, suitable plant species for ovipositing and suitable water quality. Odonates have been used for [[bio-indication]] purposes regarding the quality of the [[ecosystem]]. Different species have different requirements for their larvae with regard to water depth, water movement and pH.<ref name=Allen2009>{{cite book |title=The ecology and conservation of threatened damselflies |last=Allen |first=Katherine |year=2009 |publisher=The Environment Agency |isbn=978-1-84911-093-8 |pages=1–6 }}</ref>
The European [[Enallagma cyathigerum|common blue damselfly]] (''Enallagma cyathigerum'') for example can occur at high densities in [[acid]] waters where fish are absent, such as in bog pools.{{sfn|Dijkstra|2006|page=102}}
The [[scarce blue-tailed damselfly]] (''Ischnura pumilio'') in contrast requires [[alkali|base-rich]] habitats and water with a slow flow-rate. It is found in ditches, quarries, seeps, flushes, marshes and pools. It tolerates high levels of zinc and copper in the sediment but requires suitable emergent plants for egg-laying without the water being choked by plants.<ref name=Allen2009/> Damselflies' dependence on freshwater habitats makes them very vulnerable to damage to wetlands through drainage for agriculture or urban growth.<ref name=Corbet1980>{{cite journal |last1=Corbet |first1=P. S. |title=Biology of Odonata |journal=Annual Review of Entomology |date=1980 |volume=25 |pages=189–217 |doi=10.1146/annurev.en.25.010180.001201 }}</ref>

In the tropics, the helicopter damselfly ''Mecistogaster modesta'' ([[Pseudostigmatidae]]) breeds in [[phytotelmata]], the small bodies of water trapped by [[bromeliad]]s, [[epiphytic]] plants of the [[rainforest]] of northwest [[Costa Rica]], at the high density of some 6000 larvae per hectare in patches of secondary forest.<ref>{{cite journal |last1=Srivastava |first1=Diane S. |last2=Melnychuk |first2=Michael C. |last3=Ngai |first3=Jacqueline T. |s2cid=53603745 |title=Landscape variation in the larval density of a bromeliad-dwelling zygopteran, Mecistogaster modesta (Odonata: Pseudostigmatidae) |journal=International Journal of Odonatology |date=2005 |volume=8 |issue=1 |pages=67–79 |doi=10.1080/13887890.2005.9748244 |bibcode=2005IJOdo...8...67S }}</ref> Another tropical species, the cascade damselfly ''[[Thaumatoneura inopinata]]'' ([[Megapodagrionidae]]), inhabits [[waterfall]]s in Costa Rica and Panama.<ref>{{cite journal|title=Studies on Costa Rican Odonata. V. The waterfall-dwellers: Thaumatoneura imagos and possible male dimorphism|author=Calvert, Philip P.|journal=Entomological News and Proceedings of the Entomological Section|volume=25|issue=8|year=1914|pages=337–348|url= https://archive.org/stream/entomologicalnew25acad#page/n421/mode/2up}}</ref><ref>{{cite iucn |author=Paulson, D. R. |date=2009 |title=''Thaumatoneura inopinata'' |volume=2009 |page=e.T21721A9313826 |doi=10.2305/IUCN.UK.2009-2.RLTS.T21721A9313826.en |access-date=13 November 2021}}{{Dead link|date=August 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Damselflies, both nymphs and adults, are eaten by a range of [[predators]] including birds, fish, frogs, dragonflies, other damselflies, [[Diving bell spider|water spiders]], [[water beetle]]s, [[Notonectidae|backswimmers]] and [[Belostomatidae|giant water bugs]].<ref name=Acorn>{{cite book|author=Acorn, John|title=Damselflies of Alberta: Flying Neon Toothpicks in the Grass |url=https://archive.org/details/damselfliesofalb00acor |url-access=registration|year=2004 |publisher=University of Alberta |isbn=978-0-88864-419-0|pages=[https://archive.org/details/damselfliesofalb00acor/page/9 9]–15}}</ref>

Damselflies have a variety of internal and external parasites. Particularly prevalent are the [[Gregarinasina|gregarine protozoans]] found in the gut. In a study of the European common blue damselfly, every adult insect was infected at the height of the flying season. When present in large numbers, these parasites can cause death by blocking the gut.<ref name="Acorn" /> Water mites [[Hydrachnidiae|Hydracarina]] are often seen on the outside of both nymphs and adults, and can move from one to the other at metamorphosis.<ref name="Acorn" /> They suck the body fluids and may actually kill young nymphs, but adults are relatively unaffected, it being necessary for the completion of the mite's life cycle that it returns to water, a feat accomplished when the adult damselfly breeds.<ref>{{cite book|author=Proctor, Heather |title=Aquatic Mites from Genes to Communities: From Genes to Communities |url=https://books.google.com/books?id=PoOL_XRi9WsC&pg=PA91 |year=2004 |publisher=Springer Science & Business Media |isbn=978-1-4020-2703-1 |pages=79–84}}</ref>

=== Behaviour ===

[[File:Blue-fronted Dancer (Argia apicalis) (14681891387).jpg|thumb|left|Female blue-fronted dancer]]

Many damselflies have elaborate courtship behaviours. These are designed to show off the male's distinctive characteristics, bright colouring or flying abilities, thus demonstrating his fitness. ''[[Calopteryx (damselfly)|Calopteryx]]'' males will hover in front of a female with alternating fast and slow wingbeats; if she is receptive she will remain perched, otherwise she will fly off. The male [[Calopteryx aequabilis|river jewelwing]] (''Calopteryx aequabilis'') performs display flights in front of the female, fluttering his forewings while keeping his hindwings still, and raising his abdomen to reveal the white spots on his wings.{{sfn|Paulson|2009|page=42}}  ''[[Platycypha]]'' males will hover in front of a female, thrusting their bright white legs forward in front of their heads. Flattened tibia and bright leg colouring are seen in ''[[Platycnemis phasmovolans]]'' and a few other [[Platycnemididae]], including the extinct ''[[Yijenplatycnemis huangi]]''.<ref name="Zheng Nel 2017">{{cite journal |last1=Zheng |first1=Daran |last2=Nel |first2=André |last3=Jarzembowski |first3=Edmund A. |last4=Chang |first4=Su-Chin |last5=Zhang |first5=Haichun |last6=Xia |first6=Fangyuan |last7=Liu |first7=Haoying |last8=Wang |first8=Bo |date=2017 |title=Extreme adaptations for probable visual courtship behaviour in a Cretaceous dancing damselfly |journal=Scientific Reports |volume=7 |issue=1 |pages=44932 |doi=10.1038/srep44932 |issn=2045-2322 |pmc=5357891 |pmid=28317876 |bibcode=2017NatSR...744932Z }}</ref> ''[[Rhinocypha]]'' bobs up and down, often low over fast-flowing forested and shaded streams, displaying its bright-coloured body and wings.<ref name="Silsby 2001 p58"/> Some species (''R. biceriata'', ''R. humeralis'') have a foot waggling behaviour: they thrust a leg forward and vibrate it towards ovipositing females while in flight.<ref name="Orr 1996">{{cite journal |last=Orr |first=A. G. |date=1996 |title=Territorial and courtship displays in Bornean Chlorocyphidae (Zygoptera) |url=https://natuurtijdschriften.nl/pub/592155/OJIOS1996025002002.pdf |journal=Odonatologica |volume=25 |issue=2 |pages=119–141}}</ref> Vibrating the tibia is seen in ''Libellago semiopaca'' despite it lacking bright colouration on the tibia suggesting that foot waggling is a generalized excitary signal in Chlorocyphidae damselflies.<ref name="Orr 1996"/>  Foot waggling has been observed in ''Calopteryx'' sp., ''[[Platycypha fitzsimonsi]]'',<ref name="Robertson 1982">{{cite journal |last=Robertson |first=H. M. |date=1982 |title=Courtship displays and mating behaviour of three species of Chlorocyphida (Zygoptera) |url=https://natuurtijdschriften.nl/pub/591569/OJIOS1982011001007.pdf |journal=Odonatologica |volume=11 |issue=1 |pages=53–58}}</ref> and ''[[Platycypha caligata]]''. Male members of the family [[Protoneuridae]] with vividly coloured wings display these to visiting females.<ref name="Silsby 2001 p58">{{cite book |last=Silsby |first=Jill |title=Dragonflies of the World |url=https://books.google.com/books?id=ddzwJiuRP48C&pg=PA58 |year=2001 |publisher=Csiro Publishing |isbn=978-0-643-10249-1 |pages=58–59}}</ref> [[Ischnura erratica|Swift forktail]] (''Ischnura erratica'') males display to each other with their blue-tipped abdomens raised.{{sfn|Paulson|2009|page=108}}

[[File:Euphaea fraseri-Aralam-2016-10-29-001.jpg|thumb|upright|''[[Euphaea fraseri]]'' males [[Territory (animal)#Resources defended|defend their territory]], with open wings and prominently [[Display (zoology)#Among animals|display]] the iridescent copper markings of the upper hind wing.]]

Other behaviours observed in damselflies include wing-warning, wing-clapping, flights of attrition and abdominal bobbing. Wing-warning is a rapid opening and closing of the wings and is aggressive, while wing-clapping involves a slower opening of the wings followed by a rapid closure, up to eight times in quick succession, and often follows flight; it may serve a thermo-regulatory function.<ref name=Bick>{{cite journal |author1=Bick, George H. |author2=Bick, Juanda C. |year=1961 |title=Demography and Behavior of the Damselfly, ''Argia Apicalis'' (Say), (Odonata: Coenagriidae) |journal=Ecology |volume=46 |issue=4 |pages=461–472 |jstor=1934877 |doi=10.2307/1934877}}</ref> Flights of attrition are engaged in by the [[ebony jewelwing]] (''Calopteryx maculata'') and involve males bouncing around each other while flying laterally and continuing to do so, sometimes over a considerable distance, until one insect is presumably exhausted and gives up.{{sfn|Paulson|2009|page=44}} Characteristics of displays and coloration of males are suggested to be the common cues used by females to choose mates. In at least one species, ''Mnais costalis'', males with more sunlight in their territories had higher wing-beat frequency and were more likely to mate. Females preferred "hotter" males because they would be on warmer territories for egg laying.<ref>{{Cite journal |last1=Tsubaki |first1=Yoshitaka |last2=Samejima |first2=Yuka |last3=Siva-Jothy |first3=Michael T. |date=2010 |title=Damselfly females prefer hot males: higher courtship success in males in sunspots |url=https://doi.org/10.1007/s00265-010-0968-2 |journal=Behavioral Ecology and Sociobiology |language=en |volume=64 |issue=10 |pages=1547–1554 |doi=10.1007/s00265-010-0968-2 |bibcode=2010BEcoS..64.1547T |issn=1432-0762}}</ref>

At night, damselflies usually roost in dense vegetation, perching with the abdomen alongside a stem. If disturbed they will move around to the other side of the stem but will not fly off. Spreadwings fully fold their wings when roosting.<ref name=Paulson2011/> The [[Palaemnema domina|desert shadowdamsel]] (''Palaemnema domina'') aggregates to roost in thick places near streams in the heat of the day. While there it engages in wing-clapping, the exact function of which is unknown.{{sfn|Paulson|2009|page=185}} Some species such as the rubyspot damselfly, ''[[American rubyspot|Hetaerina americana]]'', form night roosting aggregations, with a preponderance of males; this may have an anti-predator function or may be simply the outcome of choosing safe roosting sites.<ref name=Switzer>{{cite journal |last1=Switzer |first1=Paul V.|last2=Grether|first2=Gregory F.|title=Characteristics and Possible Functions of Traditional Night Roosting Aggregations in Rubyspot Damselflies |journal=Behaviour |date=2000 |volume=137 |issue=4|pages=401–416 |url=https://www.eeb.ucla.edu/Faculty/Grether/PDF/Switzer&Grether2000.pdf |doi=10.1163/156853900502141 |s2cid=85986224 }}</ref>

===Reproduction===
Mating in damselflies, as in dragonflies, is a complex, precisely choreographed process involving both indirect insemination and delayed fertilisation.{{sfn|Dijkstra|2006|pages=8–9}}<ref name=Battin>{{cite journal|last1=Battin |first1=Tom |title=The odonate mating system, communication, and sexual selection: A review |journal= Bolletino di Zoologia|date=1993 |volume=60 |issue=4 |pages=353–360 |doi=10.1080/11250009309355839 |doi-access=free }}</ref> The male first has to attract a female to his territory, continually driving off rival males. When he is ready to mate, he transfers a packet of sperm from his primary genital opening on segment 9, near the end of his abdomen, to his secondary genitalia on segments 2–3, near the base of his abdomen. The male then grasps the female by the head with the claspers at the end of his abdomen; the structure of the claspers varies between species, and may help to prevent interspecific mating.<ref name=Battin/><ref name=Cordero>{{cite book |last1=Cordero-Rivera |first1=Adolfo |last2=Cordoba-Aguilar |first2=Alex |chapter=Selective Forces Propelling Genitalic Evolution in Odonata |year=2010 |page=343 |chapter-url=http://ecoevo.uvigo.es/pdf/2010/2010-Genital%20evolution%20odonata-lq.pdf |title=The Evolution of Primary Sexual Characters in Animals |editor=Leonard, Janet |editor2=Alex Córdoba-Aguilar |publisher=Oxford University Press |access-date=2015-03-16 |archive-date=2015-02-25 |archive-url=https://web.archive.org/web/20150225124220/http://ecoevo.uvigo.es/pdf/2010/2010-Genital%20evolution%20odonata-lq.pdf |url-status=dead }}</ref> The pair fly in tandem with the male in front, typically perching on a twig or plant stem. The female then curls her abdomen downwards and forwards under her body to pick up the sperm from the male's secondary genitalia, while the male uses his "tail" claspers to grip the female behind the head: this distinctive posture is called the "heart" or "wheel";{{sfn|Dijkstra|2006|pages=8–9}}{{sfn|Trueman|Rowe|2009|page=Life Cycle and Behavior}} the pair may also be described as being "in cop".{{sfn|Berger|2004|p=39|ps=: <q>Romantic souls are pleased to note that at the climactic moment, the two slender bodies form a delicate heart shape. Experts say the pair is now 'in cop'.</q>}} Males may transfer the sperm to their secondary genitalia either before a female is held, in the early stage when the female is held by the legs or after the female is held between the terminal claspers. This can lead to variations in the tandem postures.<ref>{{cite journal|doi=10.1093/aesa/58.4.592|pmid=5834678|title=Sperm Transfer in Damselflies (Odonata: Zygoptera)|journal=Annals of the Entomological Society of America|volume=58|issue=4|pages=592|year=1965|last1=Bick|first1=G. H.|last2=Bick|first2=J. C.}}</ref> The spermatophore may also have nutrition in addition to sperms as a "[[nuptial gift]]".<ref>{{cite book|last1=Cordero Rivera |first1= A|last2=Cordoba-Aguilar |first2=A |year=2010| chapter=Selective forces propelling genitalic evolution in Odonata|editor1=  Leonard J|editor2=Cordoba-Aguilar, A |title=  The evolution of primary characters in animals|publisher= Oxford University Press|place= New York|pages= 332–352}}</ref> Some cases of [[sexual cannibalism]] exist where females (of ''[[Ischnura graellsii]]'') eat males while in copula.<ref>{{cite journal|doi=10.1127/entom.gen/17/1992/17|url=http://ecoevo.uvigo.es/PDF/Entomol_Gener_vol_17_pp_17-20_(1992).pdf|journal=Entomologia Generalis|volume=17|issue=1|year=1992|pages=17–20|title=Sexual Cannibalism in the Damselfly Species Ischnura graellsii (Odonata: Coenagrionidae)|author=Cordero, Adolfo|access-date=2017-04-28|archive-url=https://web.archive.org/web/20130613025042/http://ecoevo.uvigo.es/PDF/Entomol_Gener_vol_17_pp_17-20_%281992%29.pdf|archive-date=2013-06-13|url-status=dead}}</ref>

[[Parthenogenesis]] (reproduction from unfertilised eggs) is exceptional, and has only been recorded in nature in female ''[[Ischnura hastata]]'' on the [[Azores Islands]].<ref name=diversity /><ref>{{cite journal |journal= Heredity |volume=103|issue=5|pages=377–384 |doi=10.1038/hdy.2009.65 |pmid=19513091|year= 2009 |title=Thelytokous parthenogenesis in the damselfly ''Ischnura hastata'' (Odonata, Coenagrionidae): genetic mechanisms and lack of bacterial infection |first1=M. O. |last1=Lorenzo-Carballa |first2= A. |last2=Cordero-Rivera|doi-access=free|bibcode=2009Hered.103..377L }}</ref>

Egg-laying (ovipositing) involves not only the female darting over floating or waterside vegetation to deposit eggs on a suitable substrate, but the male hovering above her, mate-guarding, or in some species continuing to clasp her and flying in tandem. The male attempts to prevent rivals from removing his sperm and inserting their own,<ref name=Carde>{{cite book |author1=Cardé, Ring T. |author2= Resh, Vincent H. |title=A World of Insects: The Harvard University Press Reader |url=https://books.google.com/books?id=g28jXs3CVC8C&pg=PA195 |year=2012 |publisher=[[Harvard University Press]] |isbn=978-0-674-04619-1 |pages=195–197}}</ref> a form of [[sperm competition]] (the sperms of the last mated male have the greatest chance of fertilizing the eggs, also known as sperm precedence<ref name=reshcarde>{{cite book|chapter=Odonata (Dragonflies, Damselflies)|author=Tennessen, K.J.|pages=721–729|title=Encyclopedia of Insects|edition=2|editor=Resh, Vincent H. |editor2=Ring T. Cardé|year=2009|publisher=Academic Press}}</ref>) made possible by delayed fertilisation{{sfn|Dijkstra|2006|pages=8–9}}{{sfn|Trueman|Rowe|2009|page=Life Cycle and Behavior}} and driven by [[sexual selection]].<ref name=Battin/><ref name=Cordero/> If successful, a rival male uses his penis to compress or scrape out the sperm inserted previously; this activity takes up much of the time that a copulating pair remain in the heart posture.{{sfn|Berger|2004|p=39|ps=: <q>Romantic souls are pleased to note that at the climactic moment, the two slender bodies form a delicate heart shape. Experts say the pair is now 'in cop'.</q>}} Flying in tandem has the advantage that less effort is needed by the female for flight and more can be expended on egg-laying, and when the female submerges to deposit eggs, the male may help to pull her out of the water.<ref name=Carde/>

<gallery widths="200" heights="175">
File:Ceriagrion cerinorubellum-Kadavoor-2016-04-11-002.jpg|alt=Damselflies holding each other|First stage: ''[[Ceriagrion cerinorubellum]]'' pair with male transferring sperm from the primary to the secondary sex organs
File:Ceriagrion cerinorubellum-Kadavoor-2016-04-11-003.jpg|alt=Mating damselflies in heart position|Second stage: "heart" or "wheel" position, the female receiving sperm from the male secondary sex organ
File:Pseudagrion indicum ovipositing at Kadavoor.jpg|Yellow-striped blue dart, ''[[Pseudagrion indicum]]'', laying eggs; the male (above) continues to hold the female with his claspers.
Hetaerina americana-mating.webm|''[[Hetaerina americana]]'' mating: sperm removal
File:Chalcolestes viridis laying eggs into slits in twig.jpg|Willow emerald, ''[[Chalcolestes viridis]]'', still in tandem, laying eggs into a series of slits in a twig
</gallery>

All damselflies lay their eggs inside plant tissues; those that lay eggs underwater may submerge themselves for 30 minutes at a time, climbing along the stems of aquatic plants and laying eggs at intervals.<ref name=Lawlor>{{cite book |author=Lawlor, Elizabeth P. |title=Discover Nature in Water & Wetlands: Things to Know and Things to Do |url=https://books.google.com/books?id=Xo83huW7O6YC&pg=PA94 |year=1999 |publisher=Stackpole Books |isbn=978-0-8117-2731-0 |pages=88, 94–96}}</ref> For example, the red-eyed damselfly ''[[Erythromma najas]]'' lays eggs, in tandem, into leaves or stems of floating or sometimes emergent plants; in contrast, the scarce bluetail ''[[Ischnura pumilio]]'' oviposits alone, the female choosing mostly emergent grasses and rushes, and laying her eggs in their stems either above or just below the waterline.<ref name="SmallshireSwash2014">{{cite book |last1=Smallshire |first1=Dave |last2=Swash |first2=Andy |title=Britain's Dragonflies: A Field Guide to the Damselflies and Dragonflies of Britain and Ireland: A Field Guide to the Damselflies and Dragonflies of Britain and Ireland |url=https://books.google.com/books?id=jG9UAwAAQBAJ&pg=PA96 |year=2014 |publisher=Princeton University Press |isbn=978-1-4008-5186-7 |pages=94–96}}</ref> The willow emerald ''[[Chalcolestes viridis]]'' (a spreadwing) is unusual in laying eggs only in woody plant tissue, choosing thin twigs of trees that hang over water, and scarring the bark in the process.{{sfn|Dijkstra|2006|page=84}} A possible exception is an apparent instance of [[viviparity|ovo-viviparity]], in which ''[[Heliocypha perforata]]'' was filmed in western China depositing young larvae (presumably hatched from eggs inside the female's body) onto a partly submerged branch of a tree.<ref name=Salindra>{{cite journal|last1=Salindra |first1=H. G. |last2=Dayananda|first2=K. |last3=Kitching |first3=Roger L. |title=Ovo-viviparity in the Odonata? The case of Heliocypha perforata (Zygoptera: Chlorocyphidae) |journal=International Journal of Odonatology|year=2014 |volume=17 |issue=4 |pages=181–185 |doi=10.1080/13887890.2014.959076 |bibcode=2014IJOdo..17..181D |s2cid=83520585 |doi-access=free }}</ref>

Many damselflies are able to produce more than one brood per year ([[voltinism]]); this is negatively correlated with [[latitude]], becoming more common towards the equator, except in the Lestidae.<ref name=Corbet2006>{{cite journal |last1=Corbet |first1=Philip S. |last2=Suhling |first2=Frank |last3=Soendgerath |first3=Dagmar |title=Voltinism of Odonata: a review |journal=International Journal of Odonatology|date=2006|volume=9 |issue=1 |pages=1–44 |url=https://www.researchgate.net/publication/228369286 |doi=10.1080/13887890.2006.9748261|bibcode=2006IJOdo...9....1C |s2cid=55299239 |doi-access=free }}</ref>

===Life cycle===
Damselflies are [[Hemimetabolism|hemimetabolous]] insects that have no pupal stage in their development.<ref>{{cite book|title=A Dictionary of Entomology|url=https://books.google.com/books?id=9IcmCeAjp6cC&pg=PA679 |year=2011 |publisher=CABI |isbn=978-1-84593-542-9 |page=679}}</ref> The female inserts the eggs by means of her ovipositor into slits made in water plants or other underwater [[Substrate (biology)|substrates]] and the larvae, known as naiads or nymphs, are almost all completely aquatic.<ref name=Paulson2011/> Exceptions include the Hawaiian ''[[Megalagrion oahuense]]'' and an unidentified Megapodagrionid from New Caledonia,<ref>{{cite journal |journal=Psyche: A Journal of Entomology |volume=62 |issue=4 |year=1955 |title=A terrestrial damselfly nymph (Medapodarionidae) from New Caledonia |author=Willey, Ruth Lippitt |pages=137–144 |url=http://downloads.hindawi.com/journals/psyche/1955/039831.pdf |doi=10.1155/1955/39831|doi-access=free }}</ref> which are terrestrial in their early stages.<ref name=Carde/> The [[Lestidae|spreadwings]] lay eggs above the waterline late in the year and the eggs overwinter, often covered by snow. In spring they hatch out in the meltwater pools and the nymphs complete their development before these temporary pools dry up.<ref name=Acorn/>

The nymphs are voracious [[Predation|predators]] and feed by means of a flat [[Insect mouthparts#Labium|labium]] (a toothed mouthpart on the lower jaw) that forms the so-called mask; it is rapidly extended to seize and pierce the ''[[Daphnia]]'' (water fleas), [[mosquito]] larvae, and other small aquatic organisms on which damselfly nymphs feed. They breathe by means of three large external, fin-like gills on the tip of the abdomen, and these may also serve for locomotion in the same manner as a fish's tail.<ref name=Paulson2011/> Compared to dragonfly larvae, the nymphs show little variation in form. They tend to be slender and elongate, many having morphological adaptations for holding their position in fast flowing water. They are more sensitive than dragonfly nymphs to oxygen levels and suspended fine particulate matter, and do not bury themselves in the mud.<ref name=Heckman>{{cite book |author=Heckman, Charles W. |title=Encyclopedia of South American Aquatic Insects: Odonata - Zygoptera: Illustrated Keys to Known Families, Genera, and Species in South America |url=https://books.google.com/books?id=PG_td3hm7XoC&pg=PA17 |year=2008 |publisher=Springer |isbn=978-1-4020-8176-7 |pages=17, 31–33}}</ref>

The nymphs proceed through about a dozen moults as they grow. In the later stages, the wing pads become visible. When fully developed, the nymphs climb out of the water and take up a firm stance, the skin on the thorax splits and the adult form wriggles out. This has a soft body at first and hangs or stands on its empty larval case. It pumps haemolymph into its small limp wings, which expand to their full extent. The haemolymph is then pumped back into the abdomen, which also expands fully. The [[exoskeleton]] hardens and the colours become more vivid over the course of the next few days. Most damselflies emerge in daytime, and in cool conditions the process takes several hours. On a hot day, the cuticle hardens rapidly and the adult can be flying away within half an hour.<ref name=Paulson2011/>

<gallery widths="200" heights="200">
File:Blue-tailed damselfly (Ischnura elegans) nymph.jpg|Blue-tailed damselfly (''[[Ischnura elegans]]'') nymph, showing the three tail appendages
File:Damselfly emergence-Aralam-2016-10-29-001.jpg|''[[Prodasineura verticalis]]'' female emerging from the [[exuviae|split skin of the nymph]]
</gallery>