|Aeshna juncea hovering over a pond.|
The Odonata are an order of flying insects that includes the dragonflies and damselflies. Like most other flying insects (flies, beetles, Lepidoptera and Hymenoptera), they evolved in the early Mesozoic era.Their prototypes, the giant dragonflies of the Carboniferous, 325 mya, are no longer placed in the Odonata but included in the Protodonata or Meganisoptera.
The two common groups are easily distinguished:
All Odonata have aquatic larvae called 'nymphs', and all of them, larvae and adults, are carnivorous. The adults can land, but rarely walk. Their legs are specialised for catching prey. They are almost entirely insectivorous.
Fabricius coined the term Odonata from the Ancient Greek ὀδώνodṓn (Ionic form of ὀδούςodoús) 'tooth' apparently because they have teeth on their mandibles, even though most insects also have toothed mandibles.
The word dragonfly is also sometimes used to refer to all Odonata, but odonate is a more correct English name for the group as a whole.Odonata enthusiasts avoid ambiguity by using the term true dragonfly, or simply Anisopteran, when referring to just the Anisoptera. The term Warriorfly has also been proposed. Some 5,900 species have been described in this order.
This order has traditionally been grouped together with the mayflies and several extinct orders in a group called the "Paleoptera", but this grouping might be paraphyletic. What they do share with mayflies is the nature of how the wings are articulated and held in rest (see insect flight for a detailed discussion).
In some treatments,the Odonata are understood in an expanded sense, essentially synonymous with the superorder Odonatoptera but not including the prehistoric Protodonata. In this approach, instead of Odonatoptera, the term Odonatoidea is used. The systematics of the "Palaeoptera" are by no means resolved; what can be said however is that regardless of whether they are called "Odonatoidea" or "Odonatoptera", the Odonata and their extinct relatives do form a clade.
The Anisoptera was long treated as a suborder, with a third suborder, the "Anisozygoptera" (ancient dragonflies). However, the combined suborder Epiprocta (in which Anisoptera is an infraorder) was proposed when it was found that the "Anisozygoptera" was paraphyletic, composed of mostly extinct offshoots of dragonfly evolution. The four living species placed in that group are (in this treatment) in the infraorder Epiophlebioptera, whereas the fossil taxa that were formerly there are now dispersed about the Odonatoptera (or Odonata sensu lato).World Odonata List considers Anisoptera as a suborder along with Zygoptera and Anisozygoptera as well-understood and widely preferred terms.
Tarsophlebiidae is a prehistoric family of Odonatoptera that can be considered either a basal lineage of Odonata or their immediate sister taxon.
The phylogenetic tree of the orders and suborders of odonates according to Bechly (2002):
The largest living odonate is the giant Central American helicopter damselfly Megaloprepus coerulatus (Zygoptera: Pseudostigmatidae) with a wing span of 191 mm. The heaviest living odonates are Tetracanthagyna plagiata (Anisoptera: Aeshnidae) with a wing span of 165 mm, and Petalura ingentissima (Anisoptera: Petaluridae) with a body length of 117 mm (some sources 125 mm) and wing span of 160 mm. The longest extant odonate is the Neotropical helicopter damselfly Mecistogaster linearis (Zygoptera: Pseudostigmatidae) with a body length of 135 mm. Sometimes the giant Hawaiian darner Anax strenuus (Anisoptera: Aeshnidae) is claimed to be the largest living odonate with an alleged wing span of 190 mm, but this seems to be a myth as only 152 mm wing spans are scientifically documented.
Odonata and their ancestors come from one of the oldest winged insect groups. The fossils of odonates and their cousins, including Paleozoic "giant dragonflies" like Meganeuropsis permiana from the Permian of North America, reached wing spans of up to 71 cm and a body length of 43 cm, making it the largest insect of all time. This insect belonged to the order Meganisoptera, the griffinflies, related to odonates but not part of the modern order Odonata in the restricted sense. They have one of the most complete fossil records going back 319 million years.
The smallest living dragonfly is Nannophya pygmaea (Anisoptera: Libellulidae) from east Asia, with a body length of 15 mm and a wing span of 20 mm. The smallest damselflies (and also the smallest odonates) are species of the genus Agriocnemis (Zygoptera: Coenagrionidae) with a wing span of only 17–18 mm.
These insects characteristically have large rounded heads covered mostly by well-developed, compound eyes, legs that facilitate catching prey (other insects) in flight, two pairs of long, transparent wings that move independently, and elongated abdomens. They have three ocelli and short antennae. The mouthparts are on the underside of the head and include simple chewing mandibles in the adult.
Flight in the Odonata is direct, with flight muscles attaching directly to the wings; rather than indirect, with flight muscles attaching to the thorax, as is found in the Neoptera. This allows active control of the amplitude, frequency, angle of attack, camber and twist of each of the four wings entirely independently.
In most families there is a structure on the leading edge near the tip of the wing called the pterostigma. This is a thickened, hemolymph–filled and often colorful area bounded by veins. The functions of the pterostigma are not fully known, but it most probably has an aerodynamic effectand may also have a visual function. More mass at the end of the wing may also reduce the energy needed to move the wings up and down. The right combination of wing stiffness and wing mass could reduce the energy consumption of flying. A pterostigma is also found among other insects, such as bees.
The nymphs have stockier, shorter, bodies than the adults. In addition to lacking wings, their eyes are smaller, their antennae longer, and their heads are less mobile than in the adult. Their mouthparts are modified, with the labium being adapted into a unique prehensile organ for grasping prey. Damselfly nymphs breathe through external gills on the abdomen, while dragonfly nymphs respire through an organ in their rectum.
Although generally fairly similar, dragonflies differ from damselflies in several, easily recognizable traits. Dragonflies are strong fliers with fairly robust bodies and at rest hold their wings either out to the side or out and downward (or even somewhat forward). Damselflies tend to be less robust, even rather weak appearing in flight, and when at rest most species hold their wings folded back over the abdomen (see photograph below, left). Dragonfly eyes occupy much of the animal's head, touching (or nearly touching) each other across the face. In damselflies, there is typically a gap in between the eyes.
Odonates are aquatic or semi-aquatic as juveniles. Thus, adults are most often seen near bodies of water and are frequently described as aquatic insects. However, many species range far from water. They are carnivorous (or more specifically insectivorous) throughout their life, mostly feeding on smaller insects.
Male Odonata have complex genitalia, different from those found in other insects. These include grasping cerci for holding the female and a secondary set of copulatory organs on the abdomen in which the sperm are held after being produced by the primary genitals. To mate, the male grasps the female by the thorax or head and bends her abdomen so that her own genitalia can be grasped by the copulatory organs holding the sperm.Male odonates have a copulatory organ on the ventral side of abdominal segment 2 in which they store spermatozoa; they mate by holding the female's head (Anisoptera) or thorax (Zygoptera) with claspers located at the tip of the male abdomen; the female bends her abdomen forward to touch the male organ and receive sperm. This is called the "wheel" position.
Eggs are laid in water or on vegetation near water or wet places, and hatch to produce pronymphs which live off the nutrients that were in the egg. They then develop into instars with approximately 9–14 molts that are (in most species) voracious predators on other aquatic organisms, including small fishes. The nymphs grow and molt, usually in dusk or dawn, into the flying teneral immature adults, whose color is not yet developed. These insects later transform into reproductive adults.
Odonates can act as bioindicators of water quality in rivers because they rely on high quality water for proper development in early life. Since their diet consists entirely of insects, odonate density is directly proportional to the population of prey, and their abundance indicates the abundance of prey in the examined ecosystem.Species richness of vascular plants has also been positively correlated with the species richness of dragonflies in a given habitat. This means that in a location such as a lake, if one finds a wide variety of odonates, then a similarly wide variety of plants should also be present. This correlation is not common to all bioindicators, as some may act as indicators for a different environmental factor, such as the pool frog acting as a bioindicator of water quality due to its high quantity of time spent in and around water.
In addition, odonates are very sensitive to changes to average temperature. Many species have moved to higher elevations and latitudes as global temperature rises and habitats dry out. Changes to the life cycle have been recorded with increased development of the instar stages and smaller adult body size as the average temperature increases. As the territory of many species starts to overlap, the rate hybridization of species that normally do not come in contact is increasing.If global climate change continues many members of Odonata will start to disappear. Because odonates are such an old order and have such a complete fossil record they are an ideal species to study insect evolution and adaptation. For example, they are one of the first insects to develop flight and it is likely that this trait only evolved once in insects, looking at how flight works in odonates, the rest of flight can be mapped out.
Lists of Odonata species of Australia - Britain - Canada (dragonflies | damselflies) - Estonia - Finland - France - India - Ireland - South Africa - Sri Lanka - Taiwan
A dragonfly is an insect belonging to the order Odonata, infraorder Anisoptera. Adult dragonflies are characterized by large, multifaceted eyes, two pairs of strong, transparent wings, sometimes with coloured patches, and an elongated body. Dragonflies can be mistaken for the related group, damselflies (Zygoptera), which are similar in structure, though usually lighter in build; however, the wings of most dragonflies are held flat and away from the body, while damselflies hold the wings folded at rest, along or above the abdomen. Dragonflies are agile fliers, while damselflies have a weaker, fluttery flight. Many dragonflies have brilliant iridescent or metallic colours produced by structural coloration, making them conspicuous in flight. An adult dragonfly's compound eyes have nearly 24,000 ommatidia each.
Damselflies are insects of the suborder Zygoptera in the order Odonata. They are similar to dragonflies, which constitute the other odonatan suborder, Anisoptera, but are smaller, have slimmer bodies, and most species fold the wings along the body when at rest, unlike dragonflies which hold the wings flat and away from the body. An ancient group, damselflies have existed since at least the Lower Permian, and are found on every continent except Antarctica.
The black-tailed skimmer is a dragonfly belonging to the family Libellulidae.
The blue-tailed damselfly or common bluetail is a damselfly, belonging to the family Coenagrionidae.
Meganisoptera is an extinct order of very large to gigantic insects, occasionally called griffinflies. The order was formerly named Protodonata, the "proto-Odonata", for their similar appearance and supposed relation to modern Odonata. They range in Palaeozoic times. Though most were only slightly larger than modern dragonflies, the order includes the largest known insect species, such as the late Carboniferous Meganeura monyi, Megatypus, and the even larger early Permian Meganeuropsis permiana, with wingspans of up to 71 centimetres (28 in).
The Calopterygidae are a family of damselflies, in the suborder Zygoptera. They are commonly known as the broad-winged damselflies, demoiselles, or jewelwings. These rather large damselflies have wingspans of 50–80 mm and are often metallic-coloured. The family contains some 150 species.
The Lestidae are a rather small family of cosmopolitan, large-sized, slender damselflies, known commonly as the spreadwings or spread-winged damselflies.
The Cordulegastridae are a family of Odonata (dragonflies) from the suborder Anisoptera. They are commonly known as spiketails. Some vernacular names for the species of this family are biddie and flying adder. They have large, brown or black bodies with yellow markings, and narrow unpatterned wings. Their bright eyes touch at a single point, and they can be found along small, clear, woodland streams, flying slowly 30 to 70 cm above the water. When disturbed, however, they can fly very rapidly. They usually hunt high in forest vegetation, and prefer to capture prey resting on leaves or branches.
The Himalayan relict dragonfly is one of four species of Epiprocta in the family Epiophlebiidae. They have at one time been classified as a suborder Anisozygoptera, considered as intermediate between the dragonflies and the damselflies, partly because the hind wings and fore wings are very similar in size and shape, and partly because the insect at rest holds them back over the body as damselflies do. These attributes now are known to be misleading however; the genus Epiophlebia shares a more recent ancestor with dragonflies and became separated from other Anisoptera in and around the uplifting Himalayas.
Widow Skimmer is one of the group of dragonflies known as king skimmers. The nymphs live in the water, molting and growing until they are ready to emerge from the water and then molting a final time to reveal their wings.
Megaloprepus caerulatus is a damselfly of the Forest Giant family (Pseudostigmatidae), found in wet and moist forests in Central and South America. It has the greatest wingspan of any living damselfly or dragonfly, up to 19 centimeters (7.5 inches) in the largest males. Its large size and the markings on its wings make it a conspicuous species; a hovering Megaloprepus has been described as a "pulsating blue-and-white beacon".
Thaumatoneura inopinata is a species of damselfly, sometimes called the cascade damselfly or giant waterfall damsel. It is unusual in flying among the falling water and spray from waterfalls in moist tropical or subtropical forests in Costa Rica.
Austrolestes colensonis, commonly known as the blue damselfly, is a species of damselfly of the family Lestidae. It is endemic to New Zealand and can commonly be found throughout the country, and at any time of the year. It is New Zealand's largest damselfly, and only blue odonate.
The Stenophlebiidae is an extinct family of medium-sized to large fossil odonates from the Upper Jurassic and Cretaceous period that belongs to the damsel-dragonfly grade ("anisozygopteres") within the stem group of Anisoptera. They are characterized by their long and slender wings, and the transverse shape of the discoidal triangles in their wing venation.
The Tarsophlebiidae is an extinct family of medium-sized fossil odonates from the Upper Jurassic and Lower Cretaceous period of Eurasia. They are either the most basal member of the damsel-dragonfly grade ("anisozygopteres") within the stem group of Anisoptera, or the sister group of all Recent odonates. They are characterized by the basally open discoidal cell in both pairs of wings, very long legs, paddle-shaped male cerci, and a hypertrophied ovipositor in females.
Bradinopyga geminata is a species of dragonfly in the family Libellulidae known commonly as the granite ghost. It is native to India, Sri Lanka and Thailand, where it is a common and widespread species.
The blue corporal, also known as little corporal, is a dragonfly in the Libellulidae, or skimmer family. First described as Libellula deplanata by Jules Pierre Rambur in 1842, it is common across much of the eastern United States.
Odonata are insects with an incomplete metamorphosis (hemimetabolous). The aquatic larva or nymph hatches from an egg, and develops through eight to seventeen instars before leaving the water and emerging as the winged adult or imago.
Procordulia smithii, commonly known as Smith's dragonfly or the ranger dragonfly, is a species of dragonfly that is endemic to New Zealand, as is its close relative Procordulia grayi.
No Dragonfly at present existing can compare with the immense Meganeura monyi of the Upper Carboniferous, whose expanse of wing was somewhere about twenty-seven inches.
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