DESCRIPTION
Dragonflies (suborder Anisoptera) are heavy-bodied, strong-flying insects that hold their wings horizontally when at rest. By contrast, damselflies (suborder Zygoptera) are slender-bodied weak-fliers that fold their wings over the abdomen when stationary.[5]
An adult dragonfly has the same typical division into head, thorax and abdomen as do other insects. It has a chitinous exoskeleton of hard plates held together with flexible membranes. The head is large with very short antennae. It is dominated by the two compound eyes, which cover most of its surface, each consisting of nearly 28,000 ommatidia. There are also three simple eyes. The mouthparts are adapted for biting with a toothed jaw; the flap-like labrum, at the front of the mouth, can be shot rapidly forward to catch prey.[7][8] http://en.wikipedia.org/wiki/Dragonfly#mediaviewer/File:Dragonfly.svg
LIFE CYCLE
Dragonflies are hemimetabolous insects; they do not have a pupal stage and undergo an incomplete metamorphosis into adults.[9] 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 of eggs may number as many as 1,500, and they take about a week to hatch into aquatic naiads (nymphs) which moult between six and fifteen times (depending on species) as they grow. Most of a dragonfly's life is spent in the naiad form, beneath the water's surface, using extendable jaws to catch other invertebrates (often mosquito larvae) or even vertebrates such as tadpoles and small fish.[9] They breathe through gills in their rectum, and can rapidly propel themselves by suddenly expelling water through the anus.[10] Some naiads hunt on land.[11]
The larval stage of large 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 skin begins to split at a weak spot behind the head. The adult dragonfly crawls out of its larval skin, 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.[12]
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" will emerge within a few days of each other. The springtime darner (Basiaeschna janata), for example, is suddenly very common in the spring but has disappeared a few weeks later and is not seen again until the following year. By contrast, a "summer species" will emerge 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 short lifespans.[13]
TERRITORIAL
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, and the blue dasher (Pachydiplax longipennis) will jostle other dragonflies to maintain the right to alight here.[14]
Defending a breeding territory is fairly common among male dragonflies, especially among species that congregate around ponds in large numbers. The territory will contain desirable features such as a sunlit stretch of shallow water, a special plant species or a particular substrate that is necessary 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. Some dragonflies signal ownership with striking colours on face, abdomen, legs or wings. The common whitetail (Plathemis lydia) dashes towards an intruder holding its white abdomen aloft like a flag. Other dragonflies engage in aerial dogfights or high speed chases. Any female will need to mate with the territory holder before laying her eggs.[14]
Dragonflies (suborder Anisoptera) are heavy-bodied, strong-flying insects that hold their wings horizontally when at rest. By contrast, damselflies (suborder Zygoptera) are slender-bodied weak-fliers that fold their wings over the abdomen when stationary.[5]
An adult dragonfly has the same typical division into head, thorax and abdomen as do other insects. It has a chitinous exoskeleton of hard plates held together with flexible membranes. The head is large with very short antennae. It is dominated by the two compound eyes, which cover most of its surface, each consisting of nearly 28,000 ommatidia. There are also three simple eyes. The mouthparts are adapted for biting with a toothed jaw; the flap-like labrum, at the front of the mouth, can be shot rapidly forward to catch prey.[7][8] http://en.wikipedia.org/wiki/Dragonfly#mediaviewer/File:Dragonfly.svg
LIFE CYCLE
Dragonflies are hemimetabolous insects; they do not have a pupal stage and undergo an incomplete metamorphosis into adults.[9] 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 of eggs may number as many as 1,500, and they take about a week to hatch into aquatic naiads (nymphs) which moult between six and fifteen times (depending on species) as they grow. Most of a dragonfly's life is spent in the naiad form, beneath the water's surface, using extendable jaws to catch other invertebrates (often mosquito larvae) or even vertebrates such as tadpoles and small fish.[9] They breathe through gills in their rectum, and can rapidly propel themselves by suddenly expelling water through the anus.[10] Some naiads hunt on land.[11]
The larval stage of large 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 skin begins to split at a weak spot behind the head. The adult dragonfly crawls out of its larval skin, 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.[12]
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" will emerge within a few days of each other. The springtime darner (Basiaeschna janata), for example, is suddenly very common in the spring but has disappeared a few weeks later and is not seen again until the following year. By contrast, a "summer species" will emerge 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 short lifespans.[13]
TERRITORIAL
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, and the blue dasher (Pachydiplax longipennis) will jostle other dragonflies to maintain the right to alight here.[14]
Defending a breeding territory is fairly common among male dragonflies, especially among species that congregate around ponds in large numbers. The territory will contain desirable features such as a sunlit stretch of shallow water, a special plant species or a particular substrate that is necessary 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. Some dragonflies signal ownership with striking colours on face, abdomen, legs or wings. The common whitetail (Plathemis lydia) dashes towards an intruder holding its white abdomen aloft like a flag. Other dragonflies engage in aerial dogfights or high speed chases. Any female will need to mate with the territory holder before laying her eggs.[14]