Anisoptera

Diversity

Dragonflies (Anisoptera) belong to the order Odonata. Odonata means "toothed,” and refers to the toothed mandibles of these carnivorous insects. There are two suborders within Odonata: Anisoptera and Zygoptera (damselflies). Currently there are eight recognized families and 124 genera of dragonflies, but this may change as many species are still undescribed. (von Ellenrieder, 2003; Corbet, 1980; McGavin, 2001)

Dragonflies are carnivorous insects with a lifestyle that is closely tied to freshwater aquatic habitats. Eggs are laid in or near water, and immature dragonflies have adaptations such as gills that allow them to spend the first few months to several years as aquatic nymphs, preying on other small aquatic organisms. As adults, dragonflies are agile fliers that prey on other insects. (Corbet, 1999)

Some species of dragonfly are territorial, with males that defend territories of high-quality egg-laying sites. In these species, males are often brightly colored and use aerial displays both to ward off other males and to lure females. Other species are not territorial. In these species, males do not attempt to attract females, but rather seize them as they pass by. Whichever mating strategy is employed, sperm competition is an important factor in determining how many eggs a male dragonfly will fertilize. In order to ensure that their own sperm will fertilized the majority of eggs, males remove previously deposited sperm from the sperm storage organ of the female before depositing their own sperm. Most males further ensure their paternity by guarding the female as she lays her eggs. (von Ellenrieder, 2003; McGavin, 2001; Silsby, 2001)

Geographic Range

Dragonflies are found worldwide, except in polar regions. The greatest diversity of dragonflies is found in tropical areas. (von Ellenrieder, 2003; Silsby, 2001)

Habitat

Dragonflies are nearly always found near freshwater. They lay their eggs in or close to water, and the immature dragonflies, called nymphs, are fully aquatic. Dragonflies are most abundant and diverse in and around slow-moving freshwater with submerged and emergent vegetation, for example small streams and ponds. However, they can also be found in many other freshwater habitats, including small water-filled holes, vernal pools, ditches, dikes, marshes, swamps, rivers, waterfalls and lakes. Adult dragonflies spend the majority of their time near water, but may travel miles away while hunting. They are agile fliers, and tend to hunt in open areas rather than amongst thick trees or other vegetation. (Borror, et al., 1989; McGavin, 2001; Silsby, 2001)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools

Physical Description

Dragonfly nymphs have large eyes, six legs, and a stout body that is only a few times longer than it is wide. They are typically brown or greenish and sometimes have algae growing on them. Nymphs occupy different habitats within aquatic ecosystems, and their shape reflects their habitat. Bottom dwellers are slow moving and have flat, stout, hairy bodies with short strong legs for digging. Weed dwellers are more active, and therefore have long, smooth, streamlined bodies. (Silsby, 2001)

Dragonfly nymphs have a modified mouthpart called a facial mask. The facial mask is a modified lower lip (labium) that is long and hinged and armed with a set of grasping, claw-like lobes. When a nymph senses prey nearby, it thrusts the labium rapidly forward to capture the prey between the two lobes. When folded, the facial mask covers the majority of the underside of the head, hence the name “facial mask.” (McGavin, 2000; McGavin, 2001)

Because dragonfly nymphs are entirely aquatic, they breathe by pumping water over tracheal gills in their rectal chamber. When necessary, they can rapidly expel water from the rectal chamber, moving themselves forward by jet propulsion. Dragonfly nymphs can be distinguished from damselfly nymphs by the location of their gills. Dragonfly gills are located inside the rectal chamber, and are not visible. Damselfly nymphs have three external gills at the end of their abdomen. (McGavin, 2001)

Adult dragonflies are easily recognized by their long thin bodies, two pairs of long wings and very large eyes that seem to cover most of their head. They can be distinguished from the closely-related damselflies by the round shape of their heads, their disproportionately large eyes, and the difference in shape between their two pairs of wings, which are held horizontally at rest. Unlike damselflies, the rear wings of dragonflies have a broad base. Other characteristics that distinguish dragonflies from damselflies include three anal appendages (one less than damselflies) and females with non-functional or vestigial ovipositors. (McGavin, 2001; Silsby, 2001)

Dragonflies have a short thorax, with three pairs of long, spiny legs that are slanted forward. Bristles on the legs interlock to form a basket that is used to scoop prey out of the air. The abdomens of adult dragonflies are very long, with 10 segments, and are often marked with colorful spots, bands and lines. The long wings of dragonflies can also have distinctive color patterns, as well as venation patters that can be used to sort them into families and species. The abdomens of some tropical species can change color with temperature, from bright red or blue in warm weather to a dull dark gray at lower temperatures. This may be an adaptation against to avoid detection from predators. (McGavin, 2001; Silsby, 2001; McGavin, 2001; Silsby, 2001)

In most species of dragonflies, the two sexes are similarly colored, though the male may be slightly brighter. Females may also have a slightly more stout abdomen. In a few species in the family Libellulidae, the two sexes have different patterns on their wings. (Borror, et al., 1989)

The smallest wingspan of an extant dragonfly species is 34 mm. The largest wingspan, 162 mm, belongs to the Australian species, Petalura ingentissima. (von Ellenrieder, 2003; Silsby, 2001)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful

Development

Dragonfly eggs are laid in water, on the surface of the ground near the water or inserted into submerged vegetation. The dragonfly larvae, called nymphs, spend at least a few months (sometimes several years) as aquatic predators. They have gills that allow them to remove oxygen from the water. (Gullan and Cranston, 2000; McGavin, 2001)

As they grow, dragonfly nymphs molt 8 to 15 times. After their final immature stage (instar), nymphs crawl out of the water, usually early in the morning, and attach themselves to a plant stem or rock. Here the adult stage frees itself from the nymphal exoskeleton. The adult spends the first half hour or so after emerging drying out and expanding to its full size, including expanding and hardening its wings. After this initial expansion as an adult, dragonflies do not grow, though their exoskeleton may harden some and they may change color over the first few weeks as an adult. (McGavin, 2001; Silsby, 2001)

Reproduction

Some species of dragonflies are territorial, with males that defend territories of high-quality egg-laying sites. In these species, males are often brightly colored and use aerial displays both to ward off other males and to lure females. The size of the territories depends on the species, the population density, and often the size of the male himself. Larger males are often able to defend larger territories than small males. Other species of dragonflies are not territorial. In these species, males do not attempt to attract females for copulation, but rather seize them as they pass by. It is not clear why some species of dragonflies are territorial and others are not. In general, it seems that the territorial species are also the more colorful species. (von Ellenrieder, 2003; Silsby, 2001)

Sperm competition is an important factor in determining how many eggs a male dragonfly will fertilize. Males use their specialized penis to remove previously deposited sperm from the spermatheca (the sac-like sperm storage organ of the female) before depositing their own sperm. This ensures that the majority of eggs laid by the female will be fertilized by the last male’s sperm. Most males attempt to further ensure their paternity by guarding the female as she lays her eggs. They do this either by flying nearby (“non-contact guarding”) or holding on to her while she lays the eggs (“contact guarding”). (von Ellenrieder, 2003; Borror, et al., 1989; McGavin, 2001; Silsby, 2001)

Dragonflies are sexually mature within days or weeks of entering the adult stage. In territorial species, males chose and defend a territory of good egg-laying habitat. In non-territorial species, males simply position themselves near such a habitat, and wait for females to arrive. Dragonflies and the closely related damselflies are unique in that the males have two sets of genitalia; primary genitalia near the tip of the abdomen and and secondary genitalia near the front of the abdomen. The sperm are produced in the primary genitalia and must be transfered to the secondary genitalia, which is used for copulation. Before copulation, the male transfers sperm from the primary to the secondary genitalia by bending his abdomen downward and forward to form a circle. (von Ellenrieder, 2003; Borror, et al., 1989; McGavin, 2000; McGavin, 2001; Silsby, 2001)

To copulate, the male dragonfly uses the three appendages at the end of his abdomen to grasp the female by the back of the head. When in this position, the male and female are said to be in “tandem.” If the female is cooperative, she bends her abdomen forward to connect with the secondary genitalia of the male. This position, in which the bodies of the two dragonflies form a closed circle is called the “wheel” position. During copulation, which usually occurs in flight, sperm is transferred from the male’s penis to the female’s sperm storage organ, called the spermatheca. In many species of dragonflies, the males have a specialized penis, which they use to remove sperm from previous matings before inserting their own sperm. This helps ensure that the majority of eggs laid will be fertilized by their sperm. In many species the male-female pair will remain in tandem while the female lays her eggs. In other species, the male releases the female but guards her by flying nearby and chasing off other males while she lays her eggs. Males of some species do not guard the females at all. (von Ellenrieder, 2003; Borror, et al., 1989; McGavin, 2000; McGavin, 2001; Silsby, 2001)

After copulation, female dragonflies lay dozens or hundreds of eggs. Different species place them in different places in or near freshwater. Some release them directly into the water. Others lay them on plants over the water or in mud or algae at the edge of the water.

Male dragonflies do not have to wait any amount of time between copulations. However, after laying a batch of eggs, female dragonflies must wait one to five days for the next batch to mature. (Silsby, 2001)

Dragonfly eggs usually hatch one to three weeks after laying. However, in some species, the eggs overwinter before hatching. The amount of time required for eggs to hatch can vary within a species as well. In some tropical species, the eggs survive long dry periods and hatch only when the rainy season begins. After hatching, the aquatic larvae live for six months to five years before developing into adults, depending on water temperature and food availability. Generally speaking higher water temperature and food availability promote more rapid growth and transformation into the adult stage. (Silsby, 2001)

  • Breeding season
    spring or summer

There is no parental care among dragonflies. The female dragonfly carefully chooses the location where she lays her eggs in order to provide her offspring with the best chances of surviving. However, once the eggs are laid, parents have no influence on the survival of their offspring.

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

The lifespan of dragonflies varies by species. Once in the adult stage, some species survive for a few weeks and some for several months. The average dragonfly probably has a lifespan of 6 to 8 weeks, once they reach the adult stage. However, there is quite a bit of variability. The amount of time that dragonfly nymphs spend in the aquatic stage can also range from weeks to years. In general, tropical species spend less time in the aquatic stage and more time in the adult stage than their temperate counterparts. (von Ellenrieder, 2003; Borror, et al., 1989)

Behavior

Dragonflies are solitary, rather than social creatures. The males of many species are territorial. However, individuals may congregate where resources are abundant, such as where a swarm of flying ants is emerging, or behind large animals that stir up prey. (Silsby, 2001)

Dragonflies are generally excellent fliers. Their two sets of wings beat out of phase with one another (one set is up while the other is down), and dragonflies can control both the frequency and amplitude of their wingbeats. They can also control the angles of the two sets of wings independently, and so can hover or fly forward, upward, backward or sideways. Because they can control their two sets of wings independently, dragonflies are agile fliers, and can even turn around within the space of one body length. Most species of dragonflies require a certain minimum temperature in order to fly. Dragonflies can control their temperature by stretching out on a sunny perch to warm up and changing their orientation to the sun (tipping abdomen up or down) to adjust the amount of solar heat they absorb. Some larger dragonflies can also cool themselves by gliding through the air and by circulating large amounts of blood through their abdomen. Because they require a minimum temperature in order to fly, most species are diurnal. However, there are a few species of dragonflies that hunt at night. (von Ellenrieder, 2003; McGavin, 2001)

A few species of dragonflies are migratory. However, a single generation of dragonflies does not complete a roundtrip migration. Rather, the individuals that arrive in the north each year are the offspring of individuals that flew south the previous year. For example, in North America, a generation of Pantala flavescens that spends its time as nymphs in the south flies north to breed. When their offspring mature, they fly south to breed. (Silsby, 2001)

Communication and Perception

Adult dragonflies are visual hunters, and communicate visually much more than most other insects. Because of their large eyes, they also have much better long-distance vision than most insects. Like many other insects, dragonflies can see UV light, which may aid in communication. Male dragonflies frequently employ flight displays to threaten other males or to court females. These displays vary between species and individuals but generally involve showing-off their brightest-colored body part, such as brightly colored patches on the head, legs, abdomen or wings. Males also fight aerial duels for territories, displaying their size and speed to each other. Once paired, mating dragonflies probably communicate by touch and possibly by chemical signal. (von Ellenrieder, 2003; McGavin, 2001; Silsby, 2001)

As larvae, dragonflies respond to mechanical, visual and chemical cues. They sense their prey with their compound eyes and/or with mechanoreceptors. (McGavin, 2001)

  • Other Communication Modes
  • mimicry

Food Habits

Dragonflies are generally insectivores, but they will eat nearly anything they can capture. Dragonfly nymphs have a special hinged labium that is used to capture small aquatic animals. Because the prey that a nymph can capture is primarily limited by the nymph’s size, the variety of prey increases as the nymph grows. Common prey items include aquatic insects, tadpoles, small fish, and other invertebrates. Nymphs will also readily eat other nymphs. (Dunn, 1996; McGavin, 2001)

Adult dragonflies eat flying insects, especially mosquitoes and other true flies, but also aphids, midges, small moths, butterflies and caterpillars, bees, smaller dragonflies and damselflies and just about any other insects they can capture. (Borror, et al., 1989; McGavin, 2001)

The three pairs of legs positioned near the front of the dragonfly thorax act like a net that allows dragonflies to catch prey in flight. The short front pair of legs allows the insect to feed while flying. After catching a prey item, dragonflies may eat while in flight, or perch to eat. Dragonfly adults are typically active hunters, flying around in search of prey rather than sitting in wait for prey to pass by. (McGavin, 2001)

Predation

Predators of dragonfly nymphs include fish, newts, frogs, toads, and larger odonate (dragonfly and damselfly) larvae. The primary defense of nymphs is concealment among vegetation or along the bottom. However, nymphs are also able to move quickly when necessary by rapidly expelling water from their rectal cavity. (Silsby, 2001)

Predators of adult dragonflies include fish, birds such as swallows and martins, frogs, rodents and other small mammals, lizards, spiders, small bees and wasps, and insect eating plants such as sundew. (Silsby, 2001)

Adult dragonflies are agile fliers an may escape predation by outmaneuvering their predators. Some species are camouflaged to escape detection by predators. A few species mimic more dangerous animals such as hornets, wasps or scorpions. (McGavin, 2001; Silsby, 2001)

  • Anti-predator Adaptations
  • mimic
  • cryptic

Ecosystem Roles

Both dragonfly larvae and adult dragonflies are voracious predators. The larvae are important predators in freshwater ecosystems and are prey for other species. Adult dragonflies help control populations of other insects, including mosquitoes and true flies. They are also food for many aquatic and terrestrial organisms. (Dunn, 1996; McGavin, 2001)

Dragonflies in both the nymph and adult stages can be hosts to several species of parasites, including trematodes, parasitic wasps and biting gnats in the family Ceratopogonidae. The most common dragonfly parasites are larval water mites. The small, red or green mite larvae attach themselves to the dragonfly nymph, and then to the adult dragonfly when it emerges. They feed on the dragonfly’s blood for 2 or 3 weeks, and eventually leave it to return to the water where they develop into adult mites. In most cases, the parasites do not appear to significantly harm to their host. However, very high numbers of parasites can cause deformation or lowered egg production in some individuals. (Borror, et al., 1989; Corbet, 1999; Dunkle, 2000)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Dragonflies are excellent indicators of freshwater quality. Adult dragonflies may also play an important roll in controlling populations of other insects including mosquitoes. In some tropical areas, dragonfly nymphs are intentionally kept in drinking water storage tanks to control larval mosquito populations. (von Ellenrieder, 2003; McGavin, 2001)

Dragonflies are considered a delicacy in several eastern countries. They have also been used in traditional medicine in China and Japan. (Corbet, 1999; McGavin, 2001)

Dragonflies are eaten several eastern countries. They have also been used in traditional medicine in China and Japan. (Corbet, 1980; McGavin, 2001)

Economic Importance for Humans: Negative

There are few known adverse affects of dragonflies on humans. Contrary to popular belief, adult dragonflies do not bite or sting. They are, however, host to parasitic trematodes, which can infect economically important animals such as poultry. (Corbet, 1999)

Conservation Status

Most dragonfly species are abundant and common, but a few require very specific habitats as immature nymphs. These species are at risk because their habitats are in danger. The most significant threat to dragonfly species is destruction and/or pollution of freshwater habitat by humans. Freshwater quality in many important dragonfly habitats is severely threatened by deforestation. (Silsby, 2001)

Nature preserves for the conservation of dragonflies exist in Japan, Europe and the United States. In Japan, some artificial habitats are also created and managed for the propagation of dragonflies. (von Ellenrieder, 2003)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

Odonates (dragonflies and damselflies) are widely considered among the most ancient of insect species. Fossils of dragonflies from 250 million years ago have been found. The forbearers of extant Odonates, order Protodonata, appeared as early as 325 million years ago. The largest dragonfly ever found was one of these fossils (Meganeuropsis americana), and had a wingspans as large as 71 cm (28 inches). (von Ellenrieder, 2003; Corbet, 1999)

An old name for the island of Japan, Akitsushima, means “Island of the Dragonfly.” (von Ellenrieder, 2003)

Contributors

Kari Kirschbaum (author), Animal Diversity Web.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

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.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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agricultural

living in landscapes dominated by human agriculture.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

cryptic

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.

diurnal
  1. active during the day, 2. lasting for one day.
drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

heterothermic

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.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

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.

migratory

makes seasonal movements between breeding and wintering grounds

mimicry

imitates a communication signal or appearance of another kind of organism

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

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).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Borror, D., C. Triplehorn, N. Johnson. 1989. An Introduction to the Study of Insects, 6th Edition. Orlando: Harcourt College Publishers.

Corbet, P. 1980. Biology of Odonata. Annual Review of Entomology, 25: 189-217.

Corbet, P. 1999. Dragonflies: Behavior and Ecology of Odonata. Ithaca, New York: Cornell University Press.

Dunkle, S. 2000. Dragonflies Through Binoculars: A Field Guide to Dragonflies of North America. New York: Oxford University Press.

Dunn, G. 1996. Insects of the Great Lakes Region. Ann Arbor: University of Michigan Press.

Gullan, P., P. Cranston. 2000. The Insects: An Outline of Entomology. Malden, Massachusetts: Blackwell Science, Inc.

McGavin, G. 2000. Insects, spiders and other terrestrial arthropods. London: Dorling Kindersley, Inc.

McGavin, G. 2001. Essential Entomology: An Order-by-Order Introduction. Oxford: Oxford University Press.

Needham, J., M. Westfall, M. May. 2000. Dragonflies of North America. Gainesville: Scientific Publishers, Inc.

O'Brien, M. 2001. "Michigan Odonata Survey Homepage" (On-line). Accessed February 05, 2004 at http://insects.ummz.lsa.umich.edu/MICHODO/mos.html.

Silsby, J. 2001. Dragonflies of the World. Washington, DC: Smithsonian Institution Press.

von Ellenrieder, N. 2003. Odonata (Dragonflies and Damselflies). Pp. 133-139 in A Evans, R Garrison, M Hutchins, eds. Grzimek's Animal Life Encyclopedia, Vol. 3, Second Edition. Detroit: Gale Group.