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Odonata is an order of predatory that includes the dragonflies and damselflies (as well as the Epiophlebia damsel-dragonflies). The two major groups are distinguished with dragonflies (Anisoptera) usually being bulkier with large together and wings spread up or out at rest, while damselflies (suborder Zygoptera) are usually more slender with eyes placed apart and wings folded together along body at rest. Adult odonates can land and perch, but rarely walk.
All odonates have aquatic animal called naiads or nymphs, and all of them, larvae and adults, are carnivorous and are almost entirely insectivorous, although at the larval stage they will eat anything that they can overpower, including small fish, , and even adult . The adults are superb aerial hunters and their legs are specialised for catching prey in flight.
Odonata in its narrow sense forms a subgroup of the broader Odonatoptera, which contains other dragonfly-like insects. The scientific study of the Odonata is called odonatology.
The word dragonfly usually denotes only Anisoptera, but is sometimes used to mean all Odonata. Odonata enthusiasts avoid ambiguity by using the term true dragonfly, or simply anisopteran, when they mean just the Anisoptera. An alternative term warriorfly has been proposed. (2025). 9780007151691, Collins. ISBN 9780007151691
The smallest living dragonfly is Nannophya pygmaea (Anisoptera: Libellulidae) from east Asia, with a body length of and a wing span of . The smallest damselflies (and also the smallest odonates) are species of the genus Agriocnemis (Zygoptera: Coenagrionidae) with a wing span of only .
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 pterostigma, a heavier section of the wing than nearby sections, assists in gliding. Without the pterostigmata, self-exciting vibrations known as flutter would set in on the wing above a certain critical speed, making gliding impossible. The pterostigma is also found in other insect species.
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 called a labial mask for grasping prey. Damselfly nymphs breathe through external on the abdomen, while dragonfly nymphs respire through an organ in their rectum.
The Odonata is closely related to mayflies and several extinct orders in a group called the Palaeoptera, but this grouping might be paraphyletic. What they do share with mayflies is the nature of insect flight.
Tarsophlebiidae is a prehistoric family of Odonatoptera that can be considered either a basal lineage of Odonata or their immediate sister taxon.
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 thought 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.
Cladogram of Epiprocta after Rehn et al. 2003:Cladogram of Odonatoptera including Odonata by Deregnaucourt et al. 2023.
Male Odonata have complex genitalia, different from those found in other insects. These include grasping Cercus at the tip of the abdomen for holding the female, and a secondary set of copulatory organs located between the second and third abdominal segment in which the spermatozoa are stored after being produced by the primary genitals— whose external opening is known as the genital pore, on the ninth abdominal segment. This process is called intra-male sperm translocation (ST). Because the male copulatory organ has evolved independently from that in other insects, it has been suggested the stem-group dragonflies had external sperm transfer. To mate, the male claspers grasps the female by the thorax (Zygoptera) or head (Anisoptera) while the female bends her abdomen so that her own genitalia can be grasped by the copulatory organ holding the sperm. This is known as the "wheel" position. In Anisoptera, males often mate while flying, lifting the females in the air, which typically last from a couple of seconds to a minute or two, whereas the males in Zygoptera mate while perched. They might even move to different spots during the mating process, which can make it last longer, anywhere between five and ten minutes. Male Odonata are very competitive when it comes to mating that in some species, the males use the Cercus located at the tip of the abdomen to remove the sperm of a rival male's from the female and put in his own.
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 with approximately 9–14 Moult that are (in most species) voracious on other aquatic organisms, including small . The nymphs grow and molt, usually in dusk or dawn, into the flying teneral immature adults, whose color is not yet developed. These transform into reproductive adults.
Odonates can act as bioindicators of water quality in 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.
Cannibalism
Cannibalism has been recorded in many species of odonates, at both the larval and adult stages. Cannibalism is caused by either errors in species recognition, intrasexual competition for mating, or prevention of mating harassment.
Gallery
See also
Various lists of Odonata species of different regions:
Cited sources
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