Editing Damselfly (section)

==General description==
[[File:Pseudagrion microcephalum wing 0117.svg|thumb|right|Illustration of damselfly wing. Both fore and hind wings are similar.]]
[[File:Pseudagrion caffrum abdomen detail.jpg|thumb|Terminal segments of the abdomen of a male damselfly (''[[Pseudagrion caffrum]]'') showing segments 8–10 (S8, S9, S10), the upper or superior appendages or cerci (c) and the inferior appendages or paraprocts (p)]]
[[File:Blue Damselfly Head GrantPeier.jpg|alt=Damselfly head|thumb|Damselfly head displaying [[compound eye]]s, [[Simple eye in invertebrates|ocelli]], [[Antenna (biology)|antennae]], and [[Insect mouthparts|mouth structures]]]]
[[File:Calopteryx splendens qtl7.jpg|thumb|Male (left) and female of the banded demoiselle, ''[[Calopteryx splendens]]'', showing their [[sexual dimorphism|differently coloured]] wings]]

The general body plan of a damselfly is similar to that of a dragonfly. The [[Eye#Compound eyes|compound eyes]] are large but are more widely separated and relatively smaller than those of a dragonfly. Above the eyes is the frons or forehead, below this the clypeus, and on the lower lip or labium, an extensible organ used in the capture of [[Predation|prey]]. The top of the head bears three simple eyes ([[ocelli]]), which may measure light intensity, and a tiny pair of [[Antenna (biology)|antennae]] that serve no olfactory function but may measure air speed.<ref name=Paulson2011>{{cite book |author=Paulson, Dennis |title=Dragonflies and Damselflies of the East |url=https://books.google.com/books?id=dTpjGOiHwNkC |year=2011 |publisher=Princeton University Press |isbn=978-1-4008-3966-7 |pages=10–32}}</ref> Many species are [[sexual dimorphism|sexually dimorphic]]; the males are often brightly coloured and distinctive, while the females are plainer, [[camouflage|cryptically]] coloured, and harder to identify to species. For example, in ''[[Coenagrion]]'', the Eurasian bluets, the males are bright blue with black markings, while the females are usually predominantly green or brown with black.{{sfn|Dijkstra|2006|pages=20, 104}} A few dimorphic species show female-limited polymorphism, the females being in two forms, one form distinct and the other with the patterning as in males. The ones that look like males, andromorphs, are usually under a third of the female population but the proportion can rise significantly and a theory that explains this response suggests that it helps overcome harassment by males.<ref>{{cite journal|title=A dynamical model of sexual harassment in damselflies and its implications for female-limited polymorphism|first1=Hans Van|last1=Gossum|first2=Thomas N.|last2=Sherratt| journal=Ecological Modelling|volume=210|issue=1–2|year=2008|pages=212–220|doi=10.1016/j.ecolmodel.2007.07.023|bibcode=2008EcMod.210..212V }}</ref> Some Coenagrionid damselflies show male-limited polymorphism, an even less understood phenomenon.<ref>{{cite book|chapter=The evolution of sex-limited colour polymorphism|first1=Hans Van|last1=Gossum|first2=Tom N. |last2=Sherratt|first3=Adolfo|last3=Cordero-Rivera|pages=219–229|title=Dragonflies and Damselflies. Model organisms for ecological and evolutionary research|editor=Cordoba-Aguilar, Alex|publisher=Oxford University Press|year=2008|isbn=9780199230693|chapter-url=https://books.google.com/books?id=IaAUDAAAQBAJ}}</ref>

In general, damselflies are smaller than dragonflies, the smallest being members of the genus ''[[Agriocnemis]]'' (wisps).<ref>{{cite journal |last1=Kipping |first1=Jens |last2=Martens |first2=Andreas |last3=Suhling |first3=Frank |title=Africa's smallest damselfly – a new ''Agriocnemis'' from Namibia |journal=Organisms Diversity & Evolution |date=2012 |doi=10.1007/s13127-012-0084-4 |volume=12 |issue=3 |pages=301–306|s2cid=13356379 }}</ref> However, members of the [[Pseudostigmatidae]] (helicopter damselflies or forest giants) are exceptionally large for the group, with wingspans as much as {{convert|19|cm|in|abbr=on}} in ''[[Megaloprepus]]''<ref>{{cite journal| last = Groenevelda | first = Linn F. |author2=Viola Clausnitzerb |author3=Heike Hadrysa | title = Convergent Evolution of Gigantism in Damselflies of Africa and South America? Evidence from Nuclear and Mitochondrial Sequence Data | journal = Molecular Phylogenetics and Evolution | volume = 42 | issue = 2 | pages = 339–46 | year = 2007 | doi = 10.1016/j.ympev.2006.05.040 | pmid = 16945555| bibcode = 2007MolPE..42..339G }}</ref> and body length up to {{convert|13|cm|in|abbr=on}} in ''[[Pseudostigma aberrans]]''.<ref>{{cite journal| last = Hedström | first = Ingemar |author2=Göran Sahlén | title = A key to the adult Costa Rican "helicopter" damselflies (Odonata: Pseudostigmatidae) with notes on their phenology and life zone preferences | journal = Rev. Biol. Trop. | volume = 49 | issue = 3–4 | pages = 1037–1056 | year = 2001 | url = http://www.scielo.sa.cr/scielo.php?pid=S0034-77442001000300024&script=sci_arttext | pmid = 12189786 }}</ref>

The first [[Thorax (insect anatomy)|thoracic]] segment is the prothorax, bearing the front pair of legs. The joint between head and prothorax is slender and flexible, which enables the damselfly to swivel its head and to manoeuvre more freely when flying. The remaining thoracic segments are the fused mesothorax and metathorax (together termed the [[Thorax (insect anatomy)|synthorax]]), each with a pair of wings and a pair of legs. A dark stripe known as the humeral stripe runs from the base of the front wings to the second pair of legs, and just in front of this is the pale-coloured, antehumeral stripe.<ref name=Paulson2011/>

The forewings and hindwings are similar in appearance and are membranous, being strengthened and supported by longitudinal veins that are linked by many cross-veins and that are filled with [[haemolymph]].<ref name=Silsby>{{cite book |author=Silsby, Jill |title=Dragonflies of the World |url=https://books.google.com/books?id=ddzwJiuRP48C&pg=PA9|year=2001 |publisher=Csiro Publishing |isbn=978-0-643-10249-1 |page=9}}</ref> Species markers include quadrangular markings on the wings known as the [[pterostigma]] or stigma, and in almost all species, there is a [[nodus]] near the leading edge. The thorax houses the flight muscles.<ref name=Paulson2011/> Many damselflies (e.g. Lestidae, Platycnemidae, Coenagrionidae) have clear wings, but some (Calopterygidae, Euphaeidae) have coloured wings, whether uniformly suffused with colour or boldly marked with a coloured patch. In species such as the banded demoiselle, ''[[Calopteryx splendens]]'' the males have both a darker green body and large dark violet-blue patches on all four wings, which flicker conspicuously in their aerial courtship dances; the females have pale translucent greenish wings.{{sfn|Dijkstra|2006|pages=23, 65–67}}

The abdomen is long and slender and consists of ten segments. The secondary genitalia in males are on the undersides of segments two and three and are conspicuous, making it easy to tell the sex of the damselfly when viewed from the side. The female genital opening is on the underside between segments eight and nine. It may be covered by a subgenital plate, or extended into a complex ovipositor that helps them lay eggs within plant tissue. The tenth segment in both sexes bears [[Cercus|cerci]] and in males, its underside bears a pair of paraprocts.<ref name=Paulson2011/>

Damselflies (except spreadwings, [[Lestidae]]) rest their wings together, above their bodies, whereas dragonflies rest with their wings spread diametrically apart; the spreadwings rest with their wings slightly apart. Damselflies have slenderer bodies than dragonflies, and their eyes do not overlap. Damselfly nymphs differ from dragonflies nymphs in that the [[epiproct]] and pair of [[paraproct]]s at the tip of their abdomen has been modified into caudal gills, in addition to being able to absorb oxygen through the wall of their rectum, whereas dragonflies breathe through internal rectal gills only.<ref>[http://assets.press.princeton.edu/chapters/i7940.pdf Dragonflies and Damselflies of Texas and the South-Central United States: Texas, Louisiana, Arkansas, Oklahoma, and New Mexico - Princeton University]</ref><ref>[https://books.google.com/books?id=QjgHAd_SjoAC&dq=gills+zygopterous+epiproct+paraprocts&pg=PA99 Physiology of Insects]</ref> Damselfly nymphs swim by fish-like undulations, the gills functioning like a tail. Dragonfly nymphs can forcibly expel water in their rectum for rapid escape.<ref name=btj>{{cite book|pages=187–201|title=Study of Insects|edition=6|first1=Donald J.|last1=Borror|first2=Charles A.|last2=Triplehorn|first3=Norman F.|last3=Triplehorn|place=Philadelphia|publisher=Saunders College Publishing}}</ref>