Common green darners (Anax junius) are a dragonfly species found across a majority of the Nearctic region. Their range extends across the entirety of the United States, north into southern Canada, and south into parts of Mexico. Migrants from the north can be found during the winter in Central America, including the Yucatan, Belize, and Veracruz. There are also populations in Hawaii, Tahiti, the West Indies, China, and the Kamchatka peninsula in Russia. Occasionally, common green darners will turn up in Bermuda, the United Kingdom, France, Alaska, and parts of northeastern Asia, but these individuals are carried there by storms or strong winds, and there do not seem to be any established populations in these regions. (Corbet, 1999; May, 2013; Paulson, 2011)
Adults are found in a large variety of habitats. They spend much of their time in riparian habitats, which may be close to the water where they emerged, or it may be where they will lay their eggs. Adult common green darners often perch in herbaceous vegetation, especially during the night. Since some populations migrate thousands of kilometers, they are often spotted in many different habitats during the trip. Migrations are very common along coastlines and other landmarks, so dunes and beaches are popular habitats. They also live and forage in forests, grasslands, and deserts, though nearby water sources are necessary. Nymphs are aquatic, and are found in lakes, ponds, and slow streams. They typically stick close to shore, in waters less than 0.5 m deep. (Corbet, 1999; May, 2013; Paulson, 2011; Polcyn, 1994; Russell, et al., 1998)
Common green darners are one of the larger dragonflies, growing up to about 7 or 8 cm in length. Their eyes are large, their thorax is short and robust, and their abdomen is long and slender. Their abdomen gives this type of dragonfly the common name "darner", as it resembles a darning needle. They have four large outstretched wings that attach at the thorax. Both males and females have a green thorax. On their abdomen, there is a black dorsal stripe that widens towards the end. Males have dull green eyes, their face is green, and their thorax is bright to dull green. The first segment on their abdomen is green, the next 2 to 6 segments are bright blue, after which, the abdomen fades to a dull green and then mostly dark. Females are polymorphic. On most females, the first two abdominal segments are green, then the rest is brown above and gray-green on the sides. The minority morph resembles the male in coloration. In both sexes the last 7 segments are red-purple during the teneral stage. Wings are uncolored or orange-tinted in this stage. The wings become an amber color as they age, particularly in females. Nymphs have an elongated oval abdomen, large eyes, and a large labium that can be extended to capture prey. Darner nymphs have flat labiums with pointed palps that are used to spear prey. They are typically brown or green in color. Later instars have prominent wing pads and can grow up to 3.5 to 5 cm in length. (Fraker and Luttbeg, 2012; Paulson, 2011)
Common green darners are hemimetabolous. Eggs are laid in aquatic habitats, and hatch after at least 6 or 7 days. They hatch as nymphs, and undergo 9 to 13 nymphal instars. As they reach the end of the nymphal stage, the nymphs climb out of the water and search for a place to eclose. Common green darners can actually travel quite far from the water before climbing a vertical surface, such as a plant stem. After which, the nymphal skin splits and they emerge. The wings unfurl as the wings and body expands. At this time, they are in the teneral stage, as sexually-immature adults. They have very little body fat, incompletely developed (but functional) wing muscles, and females have underdeveloped ovaries. They leave their nymphal skin, and quickly gain body mass as they spend much of their time foraging. The cuticle hardens, and their color pattern becomes more distinct as they develop into sexually-mature adults. This species has two different population types: resident and migratory populations. Residents remain in the general area from which they emerge. For residents in the north, the adults mate and oviposit in late July to August. The resulting offspring hatch and develop to mid-instars and then overwinter when temperatures drop. Total nymphal development time can take 11 to 12 months for residents, as the nymphs finish development when temperatures warm in the spring and then emerge as adults in the following June and July. Adults that migrate northward tend to arrive in the northern regions in the spring before any of the residents emerge. Migratory adults mate and oviposit in June. Unlike resident populations, nymphal development for migrant offspring takes only 3 to 5 months, and they do not overwinter. They emerge as tenerals typically around late-August and September. They often begin their migration as tenerals, feeding along the way and developing into adults. They mate and oviposit during migration and when they reach their southern destinations. The offspring produced develop during the warm southern winter, before emerging as adults and migrating north. (Corbet, 1999; Crumrine, 2005; Hopkins, et al., 2011; May, 2013; Paulson, 2011; Russell, et al., 1998)
To begin mating, a male usually just grabs a female, but the female chooses whether to mate. The male grasps the female by the top of the head or prothorax with his cerci. The pair flies away from water, and typically lands on vegetation to mate. Male dragonflies have a separation of the genital opening and the copulatory organ. At some point, likely before connecting with the female, the male transfers sperm from the genital opening under the ninth abdominal segment to the seminal vesicle under the second abdominal segment. Once the sperm is transferred, and the male and female are linked in tandem, the female swings the tip of her abdomen up to the seminal vesicle on the male, where sperm transfer occurs. Her legs also grasp the abdomen of the male. This is called the "wheel position". If the female has any sperm from a previous mating, the male will flush out the other sperm. Common green darners are polygynandrous, with both males and females mating many times with many different mates. Females often have marks on their pronotum or eyes from being grasped by males during copulation, this is sometimes seen in males as well. Resident populations in the north typically mate during the late summer, from July to August. In migratory populations, those that have migrated northward mate in June, while those that have traveled south mate in late fall. Mating also takes place during the southward migrations. Males do not necessarily defend their territory, but they are aggressive toward other males. Single males often attack mating pairs in tandem. The single males try to land on the mating pair, and the mating pair responds by fluttering their wings. The male in tandem also rapidly shakes its abdomen. In more extreme instances, the single male rams, pulls on, and bites the male in tandem. The male in tandem defends the pair by beating its wings, clinging to plants, and biting in return. In these instances, the tandem pair often gets divided or drowned. (Corbet, 1999; May, 2013; Paulson, 2011)
Once mating is complete, common green darners remain in tandem and oviposit in pairs. The pairs fly low over the water, with the male still grasping the female, and they land in the open to oviposit. They lay eggs on floating stems and leaves, including alive and dead material, as well as on woody branches. Large female dragonflies can lay huge clutches of eggs, though the clutch size of common green darners has not been reported. Females can lay multiple batches of eggs from multiple matings. Hypoxia triggers hatching of the eggs. Resident populations require about a year of development before they are sexually mature, while migratory populations mature after 3 to 5 months. (Corbet, 1999; Paulson, 2011)
Adult common green darners provide provisioning in eggs, and lay the eggs in a suitable aquatic environment. Otherwise, they provide no parental care. (Paulson, 2011)
Adults can often be seen flying over open areas, sometimes in small swarms. They are active during the day, and at dawn and dusk. To rest, common green darners perch in lower herbaceous vegetation, grasping the perch with their legs and hanging downward. They also retire to vegetation to roost during the night. Common green darners are strong fliers, with all four wings moving independently, giving them the ability to fly forward, backward, and to change directions rapidly. This allows them to be very successful hunters of other airborne prey, as well as terrestrial prey. However, their flight is significantly impacted by strong winds and unfavorable weather conditions; some are blown off course during migrations and end up across the ocean. They can often be seen hovering in place, facing into a strong breeze. Common green darners are active thermoregulators. By contracting and vibrating their wing muscles, these dragonflies can warm their bodies; they can also modulate the flow of hemolymph throughout the body to transfer heat. This allows them to be active at lower temperatures and in colder regions, without having to rely solely on the sun or other surrounding heat sources. However, they also utilize heat sources when available. On autumn migrations, they have been seen sunning themselves in the morning. Nymphs are very active, and are constantly moving in their aquatic habitat, spending much of their time hunting prey. They are solitary, and actively avoid other dragonfly nymphs. This is likely due to the threat of cannibalism and intraguild predation. Nymphs are active during the day and night. Resident populations in the north overwinter as nymphs, while migratory nymphs do not. (Corbet, 1999; Fraker and Luttbeg, 2012; Paulson, 2011; Polcyn, 1994; Russell, et al., 1998)
Some populations of common green darners undertake huge migrations every year. In mid-August to October, large groups move south from Canada and the northern United States to Mexico and other southern regions along coastlines and other areas. They can gather in huge swarms on the coast when migrating south. In these swarms, common green darners can often be found with other dragonfly species, such as variegated meadowhawks. Migrating birds are usually nearby as well. During the migration, they make frequent stops for short foraging flights to replenish their energy stores. Interspersed with the foraging flights are long migration flights of many kilometers. Migrations can take several weeks due to this stop-and-go behavior. There is also a return migration to the north in the spring, though this is undertaken by the offspring of the southern migrants. Northern migrations are largely unobserved, as it seems fewer dragonflies migrate north, or they are spread out over a longer time period. Northward swarms are rare. Northern migrants also do not return to the same bodies of water that their parents emerged from, and also likely do not return to even the same general area. Weather systems have a significant influence on migrations. Cold fronts are often a good indicator that an autumn migration will begin, while northern migrants in the spring often arrive on warm fronts. While in flight on their migrations, common green darners often utilize thermals and updrafts in their movements. During southern migrations, adults roost during the night in warm, west-facing surfaces in vegetation. In the morning, after fluttering their wings to generate enough heat, they adjust to east-facing perches in the sun to warm themselves. (Corbet, 1999; May, 2013; Russell, et al., 1998)
After eclosion and emerging from the water, tenerals may travel far from the water, before becoming sexually mature adults and returning to a different body of water. Resident adult populations likely remain in the same general area, staying near the water. Migratory populations have a huge range they travel through. Some travel from southern Canada all the way into Mexico and perhaps even farther. Migrants can move up to 140 km per day. The maximum total migration is 3,000 km, with most averaging a total of about 900 km. Once they reach their destination, they likely stay in the same general area and oviposit in a nearby body of water. (May, 2013; Paulson, 2011)
Dragonflies have exceptional vision, with very large, well-developed eyes. Their eyes are so large they wrap around their head and give almost a 360 degree view, though they cannot see well above or below them. They can easily detect movement, which allows them to detect airborne or terrestrial prey, as well as to find mates. Dragonflies can detect a wide range of colors, including UV light. Common green darners may be able to use plane polarized light to determine which direction is south, when migrating. When mating, vision is important in identifying mates, but a tactile connection is also vital. Males grasp females with their terminal appendages throughout copulation. (Corbet, 1999; Paulson, 2011)
Nymphs are voracious predators, and eat aquatic insects, zooplankton (Daphnia), Amphipoda, and other aquatic organisms, including tadpoles, larval salamanders, and even small fish. They also feed on other Odonata nymphs, including smaller conspecific nymphs. Dragonfly nymphs have a large, specialized labium they use to shoot out and stab prey with the labial palps. The labium retracts and brings the prey back to the mandibles. Adults are also carnivorous, and primarily eat insects. They usually feed on airborne insects including many Hymenoptera, flies, butterflies, and other Odonata species. They can also snatch terrestrial insects from plants and the ground including beetles, and hemipterans. (Corbet, 1999; Fraker and Luttbeg, 2012; Kerby, et al., 2011; Paulson, 2011)
Common green darner nymphs are traditionally considered the top predator in fish-less habitats, so nymphs have few predators. If they are ever found in fish-inhabited waters, then freshwater fish will readily prey on them. Frogs and aquatic insects are also predators, as well as other larger Odonata nymphs. Larger salamander larvae can also occasionally prey on common green darners. Cannibalism of smaller nymphs by larger nymphs is also a threat. To defend themselves, nymphs use the lateral spines on their abdomen and their cerci to poke and stab at predators. They can twist their abdomen in any direction for better access to the predator. If stabbing the predator does not work, as a last resort nymphs can extend the labium and use the labial hooks to stick into the predator. This can damage the labium, however, which is essential for feeding should the nymphs survive the encounter. Dragonfly nymphs also have a specialized water storage chamber in their rectum, where the gills are located. They can shoot water from the anus to quickly propel themselves forward, away from potential predators. Nymphs may also reduce activity or cease movement altogether in the presence of a predator. Additionally, their brown or green coloration serves as camouflage. More green nymphs are found in the spring and summer, when there is more vegetation in the water. Birds, spiders, robberflies, and other large dragonflies are all airborne predators of adult common green darners. Frogs and fish can also prey on adults when they are ovipositing in the water. Adult dragonflies can fly quickly and dodge predators easily and they also have very good vision that allows them to spot threats. (Corbet, 1999; Fraker and Luttbeg, 2012; Hopkins, et al., 2011; May, 2013; Paulson, 2011)
Nymphs of common green darners are traditionally considered top predators in fish-less aquatic habitats. They play a significant role in the ecosystem and have the potential to effect the community structure in their habitats by preying on other organisms. Both adults and nymphs serve as prey to a variety of other insects, birds, frogs, and even other odonates. There are several parasites and parasitoids that use common green darners as hosts. Parasitic gregarines, Prismatospora cloptoni, can be found in the midgut and hindgut of nymphs. Cysticercoids of the tapeworm Schistotaenia tenuicurris, will infect nymphs, and can be found in the hemocoel. The tapeworm kills common green darners during metamorphosis. Their definitive hosts of the tapeworms are grebe species, bird species that hunt and dive in the water, and prey on common green darner nymphs. Ectoparasitic midges, mainly species of Forcipomyia and Pterobosca, attach to the wings of common green darners and suck their hemolymphs for a day or two. The parasitoid wasp Aprostocetus polynemae lays its eggs in the eggs of common green darners, which kills the dragonfly embryos. (Corbet, 1999; Crumrine, 2005; Hopkins, et al., 2011; Smith and Cook, 2012)
Common green darners often feed on some insects that are harmful to humans, such as mosquitoes, and some agricultural pests, such as Mexican bean beetles. However, these dragonflies likely do not cause significant pest reduction, and are not a method of crop control outside natural predation. Dragonfly nymphs can sometimes be used as bioindicators of water quality; common green darter nymphs may have the potential to serve as bioindicators, though further research is necessary. (Catling, 2005; Corbet, 1999)
Common green darners have been recorded gathering in large groups to feed on honey bees in bee yards, especially queens and drones on nuptial flights. This has caused serious financial loses for beekeepers, especially during a particularly severe occurrence in 1941. Huge aggregations have the potential to destroy many hives. (Corbet, 1999)
Common green darners have been deemed a species of "least concern" and have a stable population. (Paulson, 2009)
Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
active at dawn and dusk
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
mainly lives in water that is not salty.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
An animal that eats mainly insects or spiders.
fertilization takes place within the female's body
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5? N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
uses sight to communicate
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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