Temporal range: 271–0 Ma
|A female bluetail damselfly
All damselflies are predatory; both nymphs and adults eat other insects. The nymphs are aquatic, with different species living in a variety of freshwater habitats including acid bogs, ponds, lakes and rivers. 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 courtship 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.
Fishing flies that mimic damselfly nymphs are used in wet-fly fishing. Damselflies sometimes provide the subject for personal jewellery such as brooches.
ClassificationThe Zygoptera are an ancient group, with fossils known from the lower Permian, at least 250 million years ago. All the fossils of that age are of adults, similar in structure to modern damselflies, so it is not known whether their larvae were aquatic at that time. The earliest larval odonate fossils are from the Mesozoic. Fossils of damselfly-like Protozygoptera date back further to 311–30 Mya. Well-preserved Eocene damselfly larvae and exuviae are known from fossils preserved in amber in the Baltic region.
Molecular analysis in 2013 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 7 more likely to be created. The discovered clades 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 18 extant traditional families are provisionally rearranged as follows (the 3 paraphyletic families disappearing, and many details not resolved):
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 19 cm (7.5 in) in Megaloprepus and body length up to 13 cm (5.1 in) in Pseudostigma aberrans.
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 cerci 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 they possess caudal gills (on the abdomen) whereas dragonflies breathe through the rectum. 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.
Distribution and diversityOdonates are found on all the continents except Antarctica. Although some species of dragonfly have wide distributions, damselflies tend to have smaller ranges. Most odonates breed in fresh-water; a few damselflies in the family Caenagrionidae breed in brackish water (and a single dragonfly species breeds in seawater). Dragonflies are more affected by pollution than are damselflies. The presence of odonates indicates that an ecosystem is of good quality. The most species-rich environments have a range of suitable microhabitats, providing suitable water bodies for breeding.
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. Forktails in the family Coenagrionidae seem particularly prone to do this, large male boreal bluets (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 rigs 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.
BiologyAdult 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. Although predominantly using vision to locate their prey, adults may also make use of olfactory cues. 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. In tropical South America, helicopter damselflies (Pseudostigmatidae) feed on spiders, hovering near an orb web and plucking the spider, or its entangled prey, from the web. There are few pools and lakes in these habitats, and these damselflies breed in temporary water bodies in holes in trees, the rosettes of bromeliads and even the hollow stems of bamboos.
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 crustaceans such as water fleas.
In the tropics, the helicopter damselfly Mecistogaster modesta (Pseudostigmatidae) breeds in phytotelmata, the small bodies of water trapped by bromeliads, 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 waterfalls 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, water beetles, backswimmers and giant water bugs.
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, Hetairina 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.
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.
Life cycleDamselflies are hemimetabolous insects that have no pupal stage in their development. The female inserts the eggs by means of her ovipositor into slits made in water plants or other underwater substrates and the larvae, known as naiads or nymphs, are almost all completely aquatic. Exceptions include the Hawaiian Mealagrion oahuense and an unidentified Megapodagrionid from New Caledonia, which are terrestrial in their early stages. The 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.
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.
ConservationConservation of Odonata has usually concentrated on the more iconic suborder Anisoptera, the dragonflies. However, the two suborders largely have the same needs, and what is good for dragonflies is also good for damselflies. The main threats experienced by odonates are the clearance of forests, the pollution of waterways, the lowering of groundwater levels, the damming of rivers for hydroelectric schemes and the general degradation of wetlands and marshes. The clearance of tropical rainforests is of importance because the rate of erosion increases, streams and pools dry up and waterways become clogged with silt. The presence of alien species can also have unintended consequences. In Hawaii, the introduction of the mosquitofish (Gambusia affinis) was effective in controlling mosquitoes but nearly exterminated the island's endemic damselflies. The ancient greenling Hemiphlebia mirabilis has been an important flagship species for conservation action in preserving its habitat in Australia.
In human cultureDamselfly is a 2005 short film directed by Ben O'Connor. Damselfly is also the title of a 2012 novel in the Faeble series by S. L. Naeole, and of 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.
Fishing flies that mimic damselfly nymphs are sometimes used in wet-fly fishing, where the hook and line are allowed to sink below the surface.
Damselflies have formed subjects for personal jewellery such as brooches since at least 1880.
- "Antique "Damselfly" Brooch in Silver-topped Gold with Ruby Eyes". Macklowe Gallery. Retrieved 13 March 2015.[dead link]
|Wikimedia Commons has media related to Zygoptera.|
|Wikispecies has information related to: Zygoptera|
- Berger, Cynthia (2004). Dragonflies. Stackpole Books. ISBN 978-0-8117-2971-0.
- Dijkstra, Klaas-Douwe B. (2006). Field Guide to the Dragonflies of Britain and Europe. British Wildlife Publishing. ISBN 0-9531399-4-8.
- Paulson, Dennis (2009). Dragonflies and Damselflies of the West. Princeton University Press. ISBN 1-4008-3294-2.
- Trueman, John W. H.; Rowe, Richard J. (2009). "Odonata". Tree of Life. Retrieved 25 February 2015.