Odonata is anorder ofpredatoryflying insects that includes thedragonflies anddamselflies (as well as theEpiophlebia damsel-dragonflies). The two major groups are distinguished with dragonflies (Anisoptera) usually being bulkier with largecompound eyes together and wings spread up or out at rest, while damselflies (suborderZygoptera) 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 haveaquaticlarvae callednaiads ornymphs, and all of them, larvae and adults, arecarnivorous and are almost entirelyinsectivorous, although at the larval stage they will eat anything that they can overpower, including smallfish,tadpoles, and even adultnewts. 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 broaderOdonatoptera, which contains other dragonfly-like insects.The scientific study of the Odonata is called odonatology.[1]
The worddragonfly usually denotes onlyAnisoptera, but is sometimes used to mean all Odonata.[3] Odonata enthusiasts avoid ambiguity by using the termtrue dragonfly,[4] or simplyanisopteran,[5] when they mean just the Anisoptera. An alternative termwarriorfly has been proposed.[6]
The largest living odonate is the giantCentral American helicopter damselflyMegaloprepus coerulatus (Zygoptera: Pseudostigmatidae) with a wing span of 191 mm (7.5 in). The heaviest living odonates areTetracanthagyna plagiata (Anisoptera: Aeshnidae) with a wing span of 165 mm (6.5 in), andPetalura ingentissima (Anisoptera: Petaluridae) with a body length of 117 mm (4.6 in) (some sources 125 mm (4.9 in)) and wing span of 160 mm (6.3 in). The longest extant odonate is the Neotropical helicopter damselflyMecistogaster linearis (Zygoptera: Pseudostigmatidae) with a body length of 135 mm (5.3 in).[7]
The smallest living dragonfly isNannophya pygmaea (Anisoptera: Libellulidae) from east Asia, with a body length of 15 mm (0.59 in) and a wing span of 20 mm (0.79 in). The smallest damselflies (and also the smallest odonates) are species of the genusAgriocnemis (Zygoptera: Coenagrionidae) with a wing span of only 17–18 mm (0.67–0.71 in).[8]
Maleblue ringtail (Austrolestes annulosus), a damselfly (Zygoptera:Lestidae)Dragonfly (top) and damselfly (bottom) wing shape and venation
These insects characteristically have large rounded heads covered mostly by well-developed,compound eyes, which provide good vision, legs that facilitate catching prey (other insects) in flight, two pairs of long, transparent wings that move independently, and elongated abdomens. They have threeocelli and shortantennae. Themouthparts are on the underside of the head and include simple chewingmandibles in the adult.[9]
Flight in the Odonata isdirect, with flight muscles attaching directly to the wings; rather than indirect, with flight muscles attaching to the thorax, as is found in theNeoptera. This allows active control of the amplitude, frequency, angle of attack, camber and twist of each of the four wings entirely independently.[10]
In most families, there is a structure on the leading edge near the tip of the wing called thepterostigma. 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 asflutter would set in on the wing above a certain critical speed, making gliding impossible. The pterostigma is also found in other insect species.[11]
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.[12] Damselflynymphs breathe through externalgills on the abdomen, while dragonfly nymphs respire through an organ in theirrectum.[9]
Members of thecrown group Odonata first appeared during theLate Triassic,[14] though members of theirtotal group,Odonatoptera, first appeared in theLate Carboniferous, making them one of the earliest groups of winged insects.[14] The fossils of odonates and their cousins, includingPaleozoic "giant dragonflies" likeMeganeuropsis permiana from thePermian of North America, reached wing spans of up to 71 cm (28 in) and a body length of 43 cm (17 in), making it the largest insect of all time.[15] This insect belonged to the extinct orderMeganisoptera, 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.[16]
In some treatments,[20] the Odonata are understood in an expanded sense, essentially synonymous with thesuperorderOdonatoptera, but not including the prehistoricMeganisoptera. In this approach, instead of Odonatoptera, the term Odonatoidea is used. Thesystematics 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 aclade.[21]
TheAnisoptera was long treated as a suborder, with a third suborder, the Anisozygoptera (ancient dragonflies). However, the combined suborderEpiprocta (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 livingspecies placed in that group are (in this treatment) in the infraorderEpiophlebioptera, whereas the fossiltaxa that were formerly there are now dispersed about the Odonatoptera (or Odonatasensu lato).[22][23] World Odonata List considersAnisoptera as a suborder along withZygoptera andAnisozygoptera as well-understood and widely preferred terms.[24][25]
Cladogram of Epiprocta after Rehn et al. 2003[26]:
Ovipositing flight of two pairs of azure damselflies (Coenagrion puella)
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 arecarnivorous (or more specificallyinsectivorous) throughout their life, mostly feeding on smaller insects.[28]
Male Odonata have complex genitalia, different from those found in other insects. These include graspingcerci 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 thespermatozoa 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).[29][30] 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.[31] 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.[9] 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 thecerci located at the tip of the abdomen to remove the sperm of a rival male's from the female and put in his own.[32][33]
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 intoinstars with approximately 9–14molts that are (in most species) voraciouspredators on other aquatic organisms, including smallfishes. Thenymphs 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.[citation needed]
Odonates can act asbioindicators of water quality inrivers 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 examinedecosystem.[34]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 thepool frog acting as a bioindicator of water quality due to its high quantity of time spent in and around water.[35]
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.[16]
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.[36]
^"Odonatology".www.collinsdictionary.com. Collins. Retrieved19 November 2024.
^Mickel, Clarence E. (1934). "The significance of the dragonfly name "Odonata"".Annals of the Entomological Society of America.27 (3):411–414.doi:10.1093/aesa/27.3.411.
^Norberg, R. Åke (1972). "The pterostigma of insect wings an inertial regulator of wing pitch".Journal of Comparative Physiology A.81 (1):9–22.doi:10.1007/BF00693547.S2CID23441098.
^The Biology of Dragonflies. Cambridge University Press Archive. 2018. p. 324. GGKEY:0Z7A1R071DD.No Dragonfly at present existing can compare with the immenseMeganeura monyi of theUpper Carboniferous, whose expanse of wing was somewhere about twenty-seven inches.
^Golfieri, Bruno; Hardersen, Sönke; Maiolini, Bruno; Surian, Nicola (2016). "Odonates as indicators of the ecological integrity of the river corridor: Development and application of the Odonate River Index (ORI) in northern Italy".Ecological Indicators.61:234–247.Bibcode:2016EcInd..61..234G.doi:10.1016/j.ecolind.2015.09.022.ISSN1470-160X.
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