A dragonfly is an insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera (from Greek ανισος anisos, "uneven" + πτερος pteros, "wings", because the hindwing is broader than the forewing). It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies can sometimes be mistaken for damselflies, which are morphologically similar; however, adults can be differentiated by the fact that the wings of most dragonflies are held away from, and perpendicular to, the body when at rest. Dragonflies possess six legs (like any other insect), but most of them cannot walk well. Dragonflies are among the fastest flying insects in the world. Dragonflies can fly backwards, change direction in mid-air and hover for up to a minute
Dragonflies are major predators that eat mosquitoes, and other small insects like flies, bees, ants, wasps, and very rarely butterflies. They are usually found around marshes, lakes, ponds, streams, and wetlands because their larvae, known as "nymphs", are aquatic. About 5,900 different species of dragonflies (Odonata) are known in the world today of which about 3000 belong to the Anisoptera.
Though dragonflies are predators, they themselves are subject to being preyed upon by birds, lizards, frogs, spiders, fish, water bugs, and even other large dragonflies.
- 1 Classification
- 2 Life cycle
- 3 Sex Ratios
- 4 Human Impact on Dragonfly Mortality
- 5 Flight speed
- 6 Dragonflies and damselflies
- 7 Examples of endangered species
- 8 Habitat Degradation and Extinction
- 9 Common species
- 10 Gallery
- 11 Dragonflies in culture
- 12 See also
- 13 References
- 14 External links
|This section does not cite any references or sources. (December 2012)|
Formerly, the Anisoptera were given suborder rank beside the "ancient dragonflies" (Anisozygoptera), which were believed to contain the two living species of the genus Epiophlebia and numerous fossil ones. More recently it turned out that the "Anisozygopterans" form a paraphyletic assemblage of morphologically primitive relatives of the Anisoptera. Thus, the Anisoptera (true dragonflies) are reduced to an infraorder in the new suborder Epiprocta (dragonflies in general). The artificial grouping Anisozygoptera is disbanded, its members recognized as extinct offshoots at various stages of dragonfly evolution. The two living species formerly placed there—the Asian relict dragonflies—form the infraorder Epiophlebioptera alongside Anisoptera.
Female dragonflies lay eggs in or near water, often on floating or emergent plants. When laying eggs, some species will submerge themselves completely in order to lay their eggs on a good surface. The eggs then hatch into naiads (nymphs). Most of a dragonfly's life is spent in the naiad form, beneath the water's surface, using extendable jaws to catch other invertebrates (often mosquito larvae) or even vertebrates such as tadpoles and fish. They breathe through gills in their rectum, and can rapidly propel themselves by suddenly expelling water through the anus. Some naiads even hunt on land, an aptitude that could easily have been more common in ancient times when terrestrial predators were clumsier.
The larval stage of large dragonflies may last as long as five years. In smaller species, this stage may last between two months and three years. When the naiad is ready to metamorphose into an adult, it climbs up a reed or other emergent plant. Exposure to air causes the naiad to begin breathing. The skin splits at a weak spot behind the head and the adult dragonfly crawls out of its larval skin, pumps up its wings, and flies off to feed on midges and flies. In flight the adult dragonfly can propel itself in six directions; upward, downward, forward, back, and side to side. The adult stage of larger species of dragonfly can last as long as five or six months.
The sex ratio between males and females dragonfly vary both temporally and spatially. Adult dragonflies have a high male-biased ratio at breeding habitats. The male-bias ratio has contributed partially to the females using different habitats to avoid male harassment. As seen in the Hine’s emerald dragonfly (Somatochlora hineana) male populations uses wetland habitats, while females use dry meadows and marginal breeding habitats, only migrating to the wetlands to lay their eggs or to find mating partners. Unwanted mating is energetically costly for females because it affects the amount of time that they are able to spend foraging.
Human Impact on Dragonfly Mortality
The dragonfly has a uniquely long lifespan compared to other invertebrate groups of its kind. This, coupled with its relatively low population size, makes the dragonfly susceptible to some of the smallest environmental changes caused by human beings. Roadways built near wetland areas are a prime example of this. The departments of Biology at the University of South Dakota and Ecology at Iowa State University launched a joint study with The Nature Conservancy of Illinois to observe the effects of roadways on local dragonfly populations. The estimated mean number of deaths caused by motor vehicles ranged from 2 – 35 dragonflies/km/day. The study looked at four different locations from which nine different species of dragonfly were shown to have increased mortality rates due to roadways. However, of all species found, 71% of the total dead belonged to only three species. The two species most effected by the roadways were shown to be Plathemis lydia and Libellula luctuosa. Surprisingly, these two species only represented 14% and 31% of the live dragonflies observed, respectively. There could be many reasons as to why these species were affected the most, but the leading hypothesis is that slower reaction times coupled with low flight altitude may be the cause.
Tillyard claimed to have recorded the southern giant darner flying at nearly 60 miles per hour (97 km/h) in a rough field measurement. However, the greatest reliable flight speed records are for other types of insects. In general, large dragonflies like the hawkers have a maximum speed of 10–15 metres per second (22–34 mph) with average cruising speed of about 4.5 metres per second (10 mph).
Dragonflies and damselflies
Damselflies (suborder Zygoptera), typically smaller than dragonflies, are sometimes confused with newly moulted dragonflies. However, once a dragonfly moults, it is already fully grown. There are other distinctions that set them apart: most damselflies hold their wings at rest together above the torso or held slightly open above (such as in the family Lestidae), whereas most dragonflies at rest hold their wings perpendicular to their body, horizontally or occasionally slightly down and forward. Also, the back wing of the dragonfly broadens near the base, caudal to the connecting point at the body, while the back wing of the damselfly is similar to the front wing. The eyes on a damselfly are apart; in most dragonflies the eyes touch. Notable exceptions are the Petaluridae (Petaltails) and the Gomphidae (Clubtails).
The largest living odonate by wingspan is a damselfly from South America, Megaloprepus caerulatus (Drury, 1782) while the second largest are females of the dragonfly Tetracanthagyna plagiata (Wilson, 2009). The female T. plagiata is probably the heaviest living odonate.
One study looks at the probable extinction rates of dragonflies and damselflies from 1930 to 2003. It found that both Dragonflies and Damselflies exhibit lower probable extinction rates in source habitats and higher extinction rates in sink habitats. This result is consistent with the source-sink theory. The study concludes that immigration from source to sink habitats may not be enough to compensate for the high mortality and low reproduction rates in low quality habitats. Of course, extinction rates may vary based on species or location. However, this study shows that both dragonflies and damselflies are very similar when it comes to environmental needs and preferences.
Both of these animals can be severely effected by habitat loss and degradation. Water level fluctuations in source ponds were the leading cause of dragonfly disappearance. However, the populations always seem to bounce back after the water levels return to suitable levels. This suggests that the dragonflies of that region merely migrate to nearby ponds and streams until they can return to their own habitat. This behavior can explain why dragonflies have been able to survive even with their low populations and long reproduction cycle. Extinction rates for these animals are high, but this is due to our inability to track populations in a long term setting and their tremendous biodiversity.
Examples of endangered species
Leucorrhinia caudalis is a rare dragonfly species, endangered throughout Europe. It only survived in a single population in Switzerland in the 1980s. However, it recently spread and colonized several new ponds. Recently, eight microsatellite markers were developed and tested on 24 different dragonflies from six ponds in Switzerland in order to be able to analyze the ongoing migration in this species.
Although there is evidence of the recent extension of its range of migration, the rates of migration between ponds for L. caudalis are unspecified. The ongoing migration patterns of L. caudalis were examined using Bayesian assignment tests and the migration rates related to the distance between ponds, forest zones, bodies of water, and hedgerows. The migration rates of L. caudalis are not restricted to any landscape components. The tendency of the species to disperse is mainly independent of the types of the landscape.
Somatochlora hineana (Hine's emerald dragonfly)
Somatochlora hineana This unique dragonfly currently lives in the wetlands of Wisconsin, Michigan, Illinois and Missouri and is characterized by its dazzling green eyes.This insect requires a very specific environment to survive in that it requires wetlands close to calm waters so that the larve can survive on its own for four years. This has led to it being classified as the most endangered species of Dragonfly within the United States.
Somatochlora hineana (Hine's emerald dragonfly) recovery 
The United States Fish and Wildlife Service created and completed a recovery plan to aid the species. The plan to aid the species had six steps that included:
- protect and manage extant populations
- conduct research studies
- carry out searches for additional Hine's emerald populations
- run an information and education program
- manage a reintroduction and augmentation program
- review and track recovery progress.
The programs current objective is to preserve the ecosystems where the Dragonfly lives. This plan however faces numerous challenges in the form of off-road vehicle damage and the damage by invasive plants.These challenges has shifted the focus to finding new location where the Somatochlora hineana could survive.
Nannophya pygmaea Rambur (Scarlet Dwarf)
The Nannophya pygmaea Rambur (Scarlet Dwarf) is currently an endangered species in Korea. It is a widely distributed specie in China and Japan, but the N.pygmaea is very rare in Korea. The primary habitats of N.pygmaea in Korea are recently abandoned paddy fields. The paddy fields are in oligotrophic states and as succession proceeds in these habitats, N.pygmaea disappears. The interbreeding by N.pygmaea in isolated pockets of suitable habitat can lead to the lost of genetic diversity in the long run. The N.pygmaea is a less efficient flier than other dragonfly species; therefore it makes it more difficult for them to disperse from isolated habitats.
Habitat Degradation and Extinction
Dragonflies in Japan
Dragonflies are in danger and it is likely correlated to an aggressive case of habitat degradation. A study by Taku, Shin-ichi and Izumi have questioned just how bad is the case for dragonflies whom heavily depend upon rice paddies and floodplains as sources of food and shelter. Over several hundred years, a large swath of Japan's wetlands have been completely lost, and as a result, paddy fields, ponds and creeks have served as replacement habitats for the floodplains inhabited by numerous aquatic species. The Satoyama landscape of Japan houses several species which are being threatened by urban development in an area that consists of forests, residential areas and paddy fields. Rice, a cereal crop grown in paddy fields in over 100 countries, is a staple for most of the developing world. Although crop loss can be an issue, there are far-reaching impacts on the species that rely on these fields as safe habitats in which they can thrive. For example, dragonflies are a predator to rice pest insects such as flies and act as a form of natural pest control. Without this balance, ecosystems would be overpopulated with various species of insects thereby resulting in lower crop yields and lower production. There are already species of dragonflies that are in danger of becoming extinct and any further damage may result in incalculable costs to the physical environment were they to disappear. In a study by Bambaradeniya and Amarasinghe, it was stated that the more than 50 percent of arthropod species in rice fields consist of predators.
An array of dragonfly species are at risk of losing their natural habitats due to floodplain loss over the last several years. Over the past century alone, over 60% of Japan's wetlands have been completely lost to the detriment of the species that live there. In the Miyagi Prefecture, the data shows a startling decline of 92% of total wetlands, the worst in the nation of Japan. Modern practices are to blame for these increasing trends in a study published by Kurechi. The human practice of letting fields dry out completely during the winter has created a barrier to wetland functions, driving some species to extinction like the Japanese White Stork.
In Africa, the Zambian swamps and woodlands, as well as the rainforests of the Guinea and Congo Basin, are filled with a rich and diverse group of dragonflies. In a study whose purpose was to discover the top ways in prioritizing conservation among dragonflies as well as fish, crabs and molluscs, it was noted that dragonflies took up approximately 19.7% of the protected areas in Africa, representing 82.2% of the species overall. If these areas were to be lost, the impact on the population would be enormous. The study claims that biodiversity is on a continued decline, and it will be a massive challenge for generations ahead to correctly allocate and reserve areas to protect species as needed in Africa.
Influence of roadways on adult dragonflies
Roadways have a grave effect on the lives and the ecosystems of Dragonflies. The construction of roadways near the Wetlands where dragonflies live has drastically increased the number of dragonfly deaths due to motor vehicle collisions with the insects. These motor vehicle deaths have more severe effects on the dragonflies who have relatively low flight heights causing numerous more deaths and severely lowering the population of these dragonflies in the wetlands.
- Orange emperor Anax speratus
- Common thorntail Ceratogomphus pictus
- Southern yellowjack Notogomphus praetorius
- Ivory pintail Acisoma trifidum
- Banded groundling Brachythemis leucosticta
- Broad scarlet Crocothemis erythraea
- Little scarlet Crocothemis sanguinolenta
- Black percher Diplacodes lefebvrii
- Black-tailed false-skimmer Nesciothemis farinosa
- Two-striped skimmer Orthetrum caffrum
- Epaulet skimmer Orthetrum chrysostigma
- Julia skimmer Orthetrum julia
- Red-veined dropwing Trithemis arteriosa
- Navy dropwing Trithemis furva
- Kirby's dropwing Trithemis kirbyi
- Jaunty dropwing Trithemis stictica
- Common glider Trapezostigma loewii
- Scarlet percher Diplacodes haematodes
Broad-bodied chaser (Libellula depressa)
Tau Emerald (Hemicordulia tau)
Australian emperor (Hemianax papuensis)
Common glider (Trapezostigma loewii), Darwin, Australia
Scarlet percher (Diplacodes haematodes), Queensland, Australia
Blue Dasher, (Pachydiplax longipennis), Wichita, Kansas, USA
Dragonflies in culture
In Europe, dragonflies have often been seen as sinister. Some English vernacular names, such as "devil's darning needle" and "ear cutter", link them with evil or injury. A Romanian folk tale says that the dragonfly was once a horse possessed by the devil. Swedish folklore holds that the devil uses dragonflies to weigh people's souls.:25–27 The Norwegian name for dragonflies is Øyenstikker ("eye-poker"), and in Portugal they are sometimes called tira-olhos ("eye-snatcher"). They are often associated with snakes, as in the Welsh name gwas-y-neidr, "adder's servant". The Southern United States term "snake doctor" refers to a folk belief that dragonflies follow snakes around and stitch them back together if they are injured.
For some Native American tribes they represent swiftness and activity, and for the Navajo they symbolize pure water. Dragonflies are a common motif in Zuni pottery; stylized as a double-barred cross, they appear in Hopi rock art and on Pueblo necklaces.:20–26
They have also been used in traditional medicine in Japan and China. In some parts of the world they are a food source, eaten either as adults or larvae; in Indonesia, for example, they are caught on poles made sticky with birdlime, then fried in oil as a delicacy.
In the United States dragonflies and damselflies are sought out as a hobby similar to birding and butterflying, known as oding, from the Latin name of the dragonfly order, Odonata. Oding is especially popular in Texas, where 225 different species of odonates have been observed. With care, and with dry fingers, dragonflies can be handled and released by oders, as can be done with butterflies, though it is not encouraged.
Images of dragonflies are common in Art Nouveau, especially in jewelry designs. They also appear in posters by modern artists such as Maeve Harris. They have also been used as a decorative motif on fabrics and home furnishings. Douglas, a British motorcycle manufacturer based in Bristol, named its innovatively designed postwar 350cc flat twin model the Dragonfly. Progressive rock group Coheed And Cambria often depicts a dragonfly in associated artwork.
As a seasonal symbol in Japan, the dragonfly is associated with summer and early autumn. More generally, dragonflies are symbols of courage, strength, and happiness, and they often appear in art and literature, especially haiku. The love for dragonflies is reflected by traditional (layman's) names[clarification needed] for almost all of the 200 species of dragonflies found in and around Japan. Japanese children catch large dragonflies as a game, using a hair with a small pebble tied to each end, which they throw into the air. The dragonfly mistakes the pebbles for prey, gets tangled in the hair, and is dragged to the ground by the weight.:38
Beyond this, one of Japan's historical names – Akitsushima (Kanji: 秋津島 Hiragana: あきつしま) – is an archaic form meaning "Dragonfly Islands". This is attributed to a legend in which Japan's mythical founder, Emperor Jinmu, was bitten by a mosquito, which was then promptly eaten by a dragonfly.
Human-sized, prehistoric dragonfly nymphs called "Meganulon" appear in the 1956 film Rodan, based on the extinct genus Meganeura. The main kaiju antagonist in the 2000 film Godzilla vs. Megaguirus is a variation of this fictional creature.
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- Tree of Life Odonata
- Dragonfly at DMOZ
- Identification key to dragonflies found in Ireland
- British Dragonfly Society
- Dragonflies and Damselflies (Odonata) of the United States
- Phaon (Pinhey's Heritage African Odonata Network)
- Dragonflies and damselflies on the UF / IFAS Featured Creatures Web site
- Photos of dragonflies from Asia-dragonfly.net, Africa-dragonfly.net, America-Dragonfly.net, Libellulasman.com and Odonata.su
- List of field guides to dragonflies, from the International Field Guides Database