Ecology Dragonflies and damselflies are predatory both in the aquatic nymphal and adult stages. Nymphs feed on a range of freshwater invertebrates and larger ones can prey on
tadpoles and small
fish. Naiads of one species,
Phanogomphus militaris, may even act as parasites, feeding on the gills of gravid freshwater mussels. The mating system of dragonflies is complex, and they are among the few insect groups that have a system of indirect sperm transfer along with sperm storage, delayed fertilisation, and sperm competition. Adult males vigorously defend territories near water; these areas provide suitable habitat for the nymphs to develop, and for females to lay their eggs. Swarms of feeding adults aggregate to prey on swarming prey such as emerging flying ants or termites.
on an emergent plant, the water violet Hottonia palustris'', with submerged vegetation in the background Dragonflies as a group occupy a considerable variety of habitats, but many species, and some families, have their own specific environmental requirements. Some species prefer flowing waters, while others prefer standing water. For example, the Gomphidae (clubtails) live in running water, and the Libellulidae (skimmers) live in still water. Some species live in temporary water pools and are capable of tolerating changes in water level, desiccation, and the resulting variations in temperature, but some genera such as
Sympetrum (darters) have eggs and nymphs that can resist drought and are stimulated to grow rapidly in warm, shallow pools, also often benefiting from the absence of predators there. Vegetation and its characteristics including submerged, floating, emergent, or waterside are also important. Adults may require emergent or waterside plants to use as perches; others may need specific submerged or floating plants on which to lay eggs. Requirements may be highly specific, as in
Aeshna viridis (green hawker), which lives in swamps with the water-soldier plant,
Stratiotes aloides. The chemistry of the water, including its trophic status (degree of enrichment with nutrients) and
pH can also affect its use by dragonflies. Most species need moderate conditions, not too
eutrophic, not too acidic; a few species such as
Sympetrum danae (black darter) and
Libellula quadrimaculata (four-spotted chaser) prefer acidic waters such as peat bogs, while others such as
Libellula fulva (scarce chaser) need slow-moving, eutrophic waters with reeds or similar waterside plants.
Behaviour '' male in Bulgaria Many dragonflies, particularly males, are
territorial. Some defend a territory against others of their own species, some against other species of dragonfly and a few against insects in unrelated groups. A particular perch may give a dragonfly a good view over an insect-rich feeding ground; males of many species such as the
Pachydiplax longipennis (blue dasher) jostle other dragonflies to maintain the right to alight there. Defending a breeding territory is common among male dragonflies, especially in species that congregate around ponds. The territory contains desirable features such as a sunlit stretch of shallow water, a special plant species, or the preferred
substrate for egg-laying. The territory may be small or large, depending on its quality, the time of day, and the number of competitors, and may be held for a few minutes or several hours. Dragonflies including
Tramea lacerata (black saddlebags) may notice landmarks that assist in defining the boundaries of the territory. Landmarks may reduce the costs of territory establishment, or might serve as a spatial reference. Some dragonflies signal ownership with striking colours on the face, abdomen, legs, or wings. The
Plathemis lydia (common whitetail) dashes towards an intruder holding its white abdomen aloft like a flag. Other dragonflies engage in aerial dogfights or high-speed chases. A female must mate with the territory holder before laying her eggs. There is also
conflict between the males and females. Females may sometimes be harassed by males to the extent that it affects their normal activities including foraging and in some dimorphic species females have evolved multiple forms with some forms appearing deceptively like males. In some species females have evolved behavioural responses such as feigning death to escape the attention of males. Similarly, selection of habitat by adult dragonflies is not random, and terrestrial habitat patches may be held for up to 3 months. A species tightly linked to its birth site utilises a foraging area that is several orders of magnitude larger than the birth site.
Reproduction '', forming a "heart" Mating in dragonflies is a complex, precisely choreographed process. First, the male has to attract a female to his territory, continually driving off rival males. When he is ready to mate, he transfers a packet of sperm from his primary genital opening on segment 9, near the end of his abdomen, to his secondary genitalia on segments 2–3, near the base of his abdomen. The male then grasps the female by the head with the claspers at the end of his abdomen; the structure of the claspers varies between species, and may help to prevent interspecific mating. The pair flies in tandem with the male in front, typically perching on a twig or plant stem. The female then curls her abdomen downwards and forwards under her body to pick up the sperm from the male's secondary genitalia, while the male uses his "tail" claspers to grip the female behind the head: this distinctive posture is called the "heart" or "wheel"; the pair may also be described as being "in cop". Egg-laying (ovipositing) involves not only the female darting over floating or waterside vegetation to deposit eggs on a suitable substrate, but also the male hovering above her or continuing to clasp her and flying in tandem. This behaviour following the transfer of sperm is termed as mate guarding and the guarding male attempts to increase the probability of his sperm fertilising eggs.
Sexual selection with sperm competition occurs within the spermatheca of the female and sperm can remain viable for at least 12 days in some species. Females can fertilise their eggs using sperm from the spermatheca at any time.
Life cycle '' Dragonflies are
hemimetabolous insects; they do not have a
pupal stage and undergo an incomplete
metamorphosis with a series of nymphal stages from which the adult emerges. Eggs laid inside plant tissues are usually shaped like grains of rice, while other eggs are the size of a pinhead, ellipsoidal, or nearly spherical. A clutch may have as many as 1500 eggs, and they take about a week to hatch into aquatic
nymphs or naiads which moult between six and 15 times (depending on species) as they grow. Some naiads, such as the later stages of
Antipodophlebia asthenes, hunt on land. :
Emperor dragonfly,
Anax imperator, newly emerged and still soft, holding on to its dry
exuvia, and expanding its wings The nymph stage of dragonflies lasts up to five years in large species, and between two months and three years in smaller species. When the naiad is ready to metamorphose into an adult, it stops feeding and makes its way to the surface, generally at night. It remains stationary with its head out of the water, while its respiration system adapts to breathing air, then climbs up a
reed or other emergent plant, and moults (
ecdysis). Anchoring itself firmly in a vertical position with its claws, its
exoskeleton begins to split at a weak spot behind the head. The adult dragonfly crawls out of its nymph
exoskeleton, the
exuvia, arching backwards when all but the tip of its abdomen is free, to allow its exoskeleton to harden. Curling back upwards, it completes its emergence, swallowing air, which plumps out its body, and pumping
haemolymph into its wings, which causes them to expand to their full extent. Dragonflies in temperate areas can be categorized into two groups: an early group and a later one. In any one area, individuals of a particular "spring species" emerge within a few days of each other. The
springtime darner (
Basiaeschna janata), for example, is suddenly very common in the spring, but disappears a few weeks later and is not seen again until the following year. By contrast, a "summer species" emerges over a period of weeks or months, later in the year. They may be seen on the wing for several months, but this may represent a whole series of individuals, with new adults hatching out as earlier ones complete their lifespans.
Sex ratios The
sex ratio of male to female dragonflies varies both temporally and spatially. Adult dragonflies have a high male-biased ratio at breeding habitats. The male-bias ratio has contributed partially to the females using different habitats to avoid male harassment. As seen in Hine's emerald dragonfly (
Somatochlora hineana), male populations use wetland habitats, while females use dry meadows and marginal breeding habitats, only migrating to the wetlands to lay their eggs or to find mating partners. Unwanted mating is energetically costly for females because it affects the amount of time that they are able to spend foraging. '' in flight: The hindwings are about 90°
out of phase with the forewings at this instant, suggesting fast flight.
Flight '') in
mate guarding position with male above clasping the female behind the neck Dragonflies are powerful and agile fliers, capable of
migrating across the sea, moving in any direction, and changing direction suddenly. In flight, the adult dragonfly can propel itself in six directions: upward, downward, forward, backward, to left and to right. They have four different styles of flight. • Counter-stroking, with forewings beating 180°
out of phase with the hindwings, is used for hovering and slow flight. This style is efficient and generates a large amount of lift. • Phased-stroking, with the hindwings beating 90° ahead of the forewings, is used for fast flight. This style creates more thrust, but less lift than counter-stroking. • Synchronised-stroking, with forewings and hindwings beating together, is used when changing direction rapidly, as it maximises thrust. • Gliding, with the wings held out, is used in three situations: free gliding, for a few seconds in between bursts of powered flight; gliding in the updraft at the crest of a hill, effectively hovering by falling at the same speed as the updraft; and in certain dragonflies such as darters, when "in cop" with a male, the female sometimes simply glides while the male pulls the pair along by beating his wings. However, the greatest reliable flight speed records are for other types of insect. In general, large dragonflies like the hawkers have a maximum speed of with average cruising speed of about . Dragonflies can travel at 100 body-lengths per second in forward flight, and three lengths per second backwards.
Motion camouflage as used by fighting dragonflies In high-speed territorial battles between male
Australian emperors (
Hemianax papuensis), the fighting dragonflies adjust their flight paths to appear stationary to their rivals, minimizing the chance of being detected as they approach. To achieve the effect, the attacking dragonfly flies towards his rival, choosing his path to remain on a line between the rival and the start of his attack path. The attacker thus
looms larger as he closes on the rival, but does not otherwise appear to move. Researchers found that six of 15 encounters involved
motion camouflage.
Temperature control The flight muscles need to be kept at a suitable temperature for the dragonfly to be able to fly. Being
cold-blooded, they can raise their temperature by basking in the sun. Early in the morning, they may choose to perch in a vertical position with the wings outstretched, while in the middle of the day, a horizontal stance may be chosen. Another method of warming up used by some larger dragonflies is wing-whirring, a rapid vibration of the wings that causes heat to be generated in the flight muscles. The
green darner (
Anax junius), known for long-distance migrations, often resorts to wing-whirring before dawn to enable an early start. Dragonflies can avoid overheating on hot days by perching in the shade. Some species have dark patches on the wings which shade the body, and a few use the
obelisk posture to avoid overheating. This behaviour involves a "
handstand", perching with the body raised and the abdomen pointing towards the sun, minimising sun exposure. On a hot day, dragonflies sometimes adjust their body temperature by skimming over a water surface and briefly touching it, often three times in quick succession. This may also prevent desiccation.
Feeding '', with prey Adult dragonflies hunt on the wing using their exceptionally acute eyesight and strong, agile flight. They are almost exclusively carnivorous, eating a wide variety of insects ranging from small
midges and
mosquitoes to
butterflies,
moths,
damselflies, and smaller dragonflies. Nymphs are voracious predators, eating most living things smaller than themselves. Their staple diet is mostly
bloodworms and other insect larvae, but they also feed on
tadpoles and small fish.
Eyesight Dragonfly vision is thought to be like slow motion for humans. Dragonflies see faster than humans do; they see around 200 images per second. A dragonfly can see in 360 degrees, and nearly 80 percent of the insect's brain is dedicated to its sight. == Predators ==