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Damselflies are of the suborder Zygoptera in the order Odonata. They are similar to dragonflies (which constitute the other odonatan suborder, Epiprocta) but are usually smaller and have slimmer bodies. Most species fold the wings along the body when at rest, unlike dragonflies which hold the wings flat and away from the body. Damselflies have existed since the Late Jurassic, and are found on every continent except Antarctica.
All damselflies are : both nymphs and adults actively hunt and eat other insects. The nymphs are aquatic, with different species living in a variety of freshwater habitats including acidic , , and . The nymphs moult repeatedly, at the last moult climbing out of the water to undergo metamorphosis. The skin splits down the back, they emerge and inflate their wings and abdomen to gain their adult form. Their presence on a body of water indicates that it is relatively unpolluted, but their dependence on freshwater makes them vulnerable to damage to their wetland habitats.
Some species of damselfly have elaborate mating behaviours. Many species are sexually dimorphic, the males often being more brightly coloured than the females. Like dragonflies, they reproduce using indirect insemination and delayed fertilisation. A mating pair form a shape known as a "heart" or "wheel", the male clasping the female at the back of the head, the female curling her abdomen down to pick up sperm from secondary genitalia at the base of the male's abdomen. The pair often remain together with the male still clasping the female while she lays eggs within the tissue of plants in or near water using a robust ovipositor.
Artificial fly that mimic damselfly nymphs are used in wet-fly fishing. Damselflies are sometimes represented in personal jewellery such as brooches.
Molecular analysis in 2021 confirms that most of the traditional families are monophyletic, but shows that the Amphipterygidae, Megapodagrionidae and Protoneuridae are paraphyletic and will need to be reorganised. The Protoneuridae in particular is shown to be composed of six clades from five families. The result so far is 27 damselfly families, with seven more likely to be created. The discovered did not agree well with traditional characteristics used to classify living and fossil Zygoptera such as wing venation, so fossil taxa will need to be revisited. The results of the analysis are show in the phylogenetic tree shown below, with the seven new or ressurrected families marked with an asterisk:
In general, damselflies are smaller than dragonflies, the smallest being members of the genus Agriocnemis (wisps). However, members of the Pseudostigmatidae (helicopter damselflies or forest giants) are exceptionally large for the group, with wingspans as much as in Megaloprepus and body length up to in Pseudostigma aberrans.
The first 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 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.
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.
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. 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.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 and in males, its underside bears a pair of paraprocts.
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 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. Dragonflies and Damselflies of Texas and the South-Central United States: Texas, Louisiana, Arkansas, Oklahoma, and New Mexico - Princeton University Physiology of Insects 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.
Although most damselflies live out their lives within a short distance of where they were hatched, some species, and some individuals within species, disperse more widely. Ischnura in the family Coenagrionidae seem particularly prone to do this, large male ( Enallagma boreale) in British Columbia often migrating, while smaller ones do not. These are known to leave their waterside habitats, flying upwards till lost from view, and presumably being dispersed to far off places by the stronger winds found at high altitudes. In this way they may appear in a locality where no damselflies were to be seen the day before. Rambur's forktail ( Ischnura ramburii) has been found, for example, on Oil platform far out in the Gulf of Mexico.
The distribution and diversity of damselfly species in the biogeographical regions is summarized here. (There are no damselflies in the Antarctic.) Note that some species are widespread and occur in multiple regions.
| 1 |
| 151 |
| 19 |
| 39 |
| 224 |
| 4 |
| 108 |
| 185 |
| 144 |
| 6 |
| 2 |
| 68 |
| 51 |
| 2 |
| 9 |
| 29 |
| 2 |
| 4 |
| 39 |
| 12 |
| 59 |
| 1 |
| 1 |
| 5 |
| 61 |
| 1266 |
| 46 |
| 404 |
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 such as Cladocera.
In the tropics, the helicopter damselfly Mecistogaster modesta (Pseudostigmatidae) breeds in phytotelmata, the small bodies of water trapped by , epiphytic plants of the rainforest of northwest Costa Rica, at the high density of some 6000 larvae per hectare in patches of secondary forest. Another tropical species, the cascade damselfly Thaumatoneura inopinata (Megapodagrionidae), inhabits in Costa Rica and Panama.
Damselflies, both nymphs and adults, are eaten by a range of predators including birds, fish, frogs, dragonflies, other damselflies, water spiders, , Notonectidae and Belostomatidae.
Damselflies have a variety of internal and external parasites. Particularly prevalent are the Gregarinasina 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. Water mites Hydrachnidiae are often seen on the outside of both nymphs and adults, and can move from one to the other at metamorphosis. 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.
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. 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. 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.
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. The 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. Some species such as the rubyspot damselfly, 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.
Parthenogenesis (reproduction from unfertilised eggs) is exceptional, and has only been recorded in nature in female Ischnura hastata on the Azores Islands.
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,
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) made possible by delayed fertilisation and driven by sexual selection. 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. 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.
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.
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. 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. A possible exception is an apparent instance of 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.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.
The nymphs are voracious Predation and feed by means of a flat 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. 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.
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.
Damselflies have formed subjects for personal jewellery such as brooches since at least 1880.
Damselfly is a 2005 short film directed by Ben O'Connor.
Damselfly is the title of a 2012 novel in the Faeble series by S. L. Naeole and of a 2018 novel by Chandra Prasad.
Modern poems with the damselfly as a subject include a 1994 poem by August Kleinzahler, which contains the lines "And that blue there, cobalt / a moment, then iridescent, / fragile as a lady's pin / hovering above the nasturtium?" The poet John Engels published "Damselfly, Trout, Heron" in his 1983 collection Weather-Fear: New and Selected Poems.
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