Editing Damselfly (section)

===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>