Dragonflies (Odonata) are an order of large-winged insects with narrow and elongated bodies. In the world of insects, dragonflies are among the best fliers and are known to possess the most advanced vision. Water is essential for the development of dragonflies, though there are rare cases where they inhabit environments without water.
They undergo incomplete metamorphosis, and both dragonflies and their larvae are voracious predators. The dragonfly order is divided into three suborders. The scientific name of the order Odonata comes from the Greek word odontos (tooth), referring to the tooth-like structure of their mandibles. Dragonflies are studied in a special branch of entomology called odonatology.
Description
Adults
Adult dragonflies have a slender, elongated body that ranges from 20 to 130 mm in length and are equipped with three pairs of legs. They are often vividly colorful, and some species even display metallic-like luster. Their bodies are frequently marked with stripes or spots, and males and females usually differ in coloration (sexual dichromatism). The weight of an adult dragonfly varies depending on the species, for example, a very small specimen may weigh about 20 mg, while a larger species, such as the Anax imperator, may weigh up to 1200 mg.
The head is large, equipped with large, compound eyes positioned on the sides. The head is highly mobile, allowing the dragonfly to turn it 180 degrees and tilt it backward by 70 degrees. The compound eyes can consist of up to 28,000 individual lenses (ommatidia). The upper part of the eye helps the dragonfly see distant objects, while the lower part focuses on closer objects. The mouthparts are robust, with sharp, tooth-like structures for biting. The antennae are short and bristle-like. The dragonfly has three simple eyes (ocelli) located on the crown of its head, which are always well developed.
The thorax consists of three parts: the prothorax, mesothorax, and metathorax. The legs are attached to the mesothorax and metathorax. The dragonfly’s thorax is adapted for efficient flight. Both pairs of wings are membranous, rich in veins, and are attached to the thorax in such a way that they move independently, giving the dragonfly great control over flight. Dragonflies cannot fold their wings backward like many other insects, and their wingspan can vary from 19 mm to 200 mm. The wings are mostly transparent, though some species have colorful patterns on them.
The legs are relatively short but are equipped with spines that help in catching prey during flight. The abdomen is elongated and consists of ten segments, ending in short bristles. The female dragonfly has reproductive organs located between the eighth and ninth segments, while the male has reproductive organs between the second and third segments of the abdomen.
Nymphs
Dragonfly nymphs (larvae) have heads that are firmly attached to their thorax. Their compound eyes are not as large as those of the adult dragonfly. The lower part of the nymph’s face forms a unique, extendable device called a mask, used for capturing prey. Nymphs have longer, stronger legs than adult dragonflies.
Their bodies are much wider and shorter, equipped with three elongated appendages at the end of the abdomen, which serve as swimming aids. Remarkably, nymphs have the ability to regenerate lost limbs, though the new ones are often less perfect than the originals.
Eggs
Dragonfly eggs measure between 0.5 and 2 mm in length. Species that lay eggs on plants have elongated eggs, while species that lay eggs freely in water have round eggs covered in a gelatinous coating.
Development
Dragonflies develop through incomplete metamorphosis, meaning they do not go through a pupal stage. Dragonfly nymphs hatch from eggs laid in water or near it. If the eggs do not enter dormancy during winter, the nymph emerges from the egg after about two to four weeks. The first stage of the nymph’s development, called the pronymph, lasts only a few minutes. During this time, the nymph does not yet resemble a dragonfly. However, once the nymph undergoes its first molt (shedding its skin), it starts to take on the characteristics of a dragonfly.
The nymph molts approximately 10 to 15 times, shedding its exoskeleton along with parts of its digestive and respiratory systems each time. The duration of the nymphal stage can vary from a few months to several years, depending on the species. Some species may remain in the nymph stage for up to five years.
Before its final molt, the nymph stops feeding and emerges from the water, typically climbing onto plant stems or sometimes directly onto the shore. Emergence from the nymphal skin, a process called ecdysis, usually occurs in warm weather during the early morning hours. The nymph firmly grips a substrate, and the adult dragonfly begins to emerge. This process takes about an hour. Once the dragonfly has fully emerged, it sits for some time, spreading its wings and drying them before it can fly.
The time to reach sexual maturity varies by species. For example, it can take anywhere from 14 days to a month. The lifespan of an adult dragonfly also varies by species. For instance, the red dragonfly lives an average of seven days, while the common darter may live for 14 days. The maximum recorded lifespan of an adult dragonfly is 60 days. However, species that overwinter as adults may live up to six months.
Lifestyle
Hunting and Diet
Both adult dragonflies and their nymphs are predators. Adults usually catch prey in flight, but some species remain stationary and wait for prey to come within reach before attacking. Larger dragonflies often consume their prey while flying. Thanks to their exceptional vision, dragonflies can detect prey from up to two meters away. They use their legs to catch prey in mid-air and then bring it to their mouth to eat. Their prey mainly consists of other flying insects, including mosquitoes and sometimes even other dragonflies.
Nymphs hunt underwater using their extendable mask, which acts as a grabbing device. They can extend the mask to a third of their body length to seize prey and bring it to their mouth. Nymphs primarily feed on the larvae of other aquatic insects.
Reproduction
Male dragonflies possess two reproductive organs: a primary organ where sperm is stored and a secondary organ located on the underside of the second abdominal segment, which is used during mating. Before mating, the male transfers sperm from the primary organ to the secondary organ.
The male then grasps the female’s head using claspers at the end of his abdomen. During mating, the female bends the tip of her abdomen to reach the male’s secondary reproductive organ. If the female has already mated with another male, the current male removes the previous sperm using a sharp filament at the tip of his reproductive organ.
After mating, the female lays her eggs, often while still being held by the male. Depending on the species, the female lays eggs in water, on aquatic plants, or on trees above the water.
In some species, the female, accompanied by the male, submerges underwater in a bubble of air while laying eggs, and they may descend to depths approaching one meter, staying submerged for up to an hour. Dragonflies orient themselves by the reflection of sunlight on water when laying eggs, but they have occasionally been known to mistake shiny car surfaces for water and lay eggs on vehicles.
Distribution
There are at least 5,956 known species of dragonflies worldwide. In Europe, there are up to 143 species, and in Russia, there are around 74 species within two suborders. Dragonflies are most commonly found in the tropics, particularly near bodies of water, and in forests where they are more abundant than butterflies.
Paleontology
Dragonflies are believed to be around 330 million years old. The earliest dragonflies are recorded in Africa and Australia. Their ancestors, known as Protodonata, originated in the Carboniferous period. The oldest existing suborder of dragonflies, Anisozygoptera, is documented from the early Mesozoic era. Today, this suborder is represented by only two species, which are found in East Asia.
Prehistoric dragonflies from the Paleozoic era were much larger than modern species, with some having wingspans of up to 700 mm. Fossil discoveries of ancient dragonflies have been found not only in Australia and Africa but also in Russia.
Benefits of Dragonflies
Dragonflies provide many ecological benefits. Since they feed on mosquitoes and other insects, they help gardeners and outdoor enthusiasts by controlling pest populations. This reduces the need for pesticides and aids in preserving the environment. Dragonflies are also helpful in reducing the spread of diseases carried by mosquitoes, horseflies, and flies.
These insects are vectors for diseases such as malaria, yellow fever, anthrax, and tularemia. However, dragonflies are indiscriminate eaters, meaning they may also consume other beneficial species. Despite this, scientists agree that the positive impact of dragonflies far outweighs any potential drawbacks.