My Science School

Dragonflies are large, fast-flying insects that can dart at speeds up to 60 km per hour. Their four wings move independently of one another and make a rattling sound. Dragonflies can also fly backwards.

1. Dragonflies Are Ancient Insects

Long before the dinosaurs roamed the Earth, dragonflies took to the air. Griffenflies (Meganisoptera), the gigantic precursors to modern dragonflies had wingspans of over two feet and dotted the skies during the Carboniferous period over 300 million years ago.

2. Dragonfly Nymphs Live In the Water

There's a good reason why you see dragonflies and damselflies around ponds and lakes: They're aquatic! Female dragonflies deposit their eggs on the water's surface, or in some cases, insert them into aquatic plants or moss. Once hatched, the nymph dragonfly spends its time hunting other aquatic invertebrates. Larger species even dine on the occasional small fish or tadpole. After molting somewhere between six and 15 times, a dragonfly nymph is finally ready for adulthood and crawls out of the water to shed its final immature skin.

3. Nymphs Breath Through Their Anus

The damselfly nymph actually breathes through gills inside its rectum. Likewise, the dragonfly nymph pulls water into its anus to facilitate gas exchange. When the nymph expels water, it propels itself forward, providing the added benefit of locomotion to its breathing.

4. Most New Dragonfly Adults Are Eaten

When a nymph is finally ready for adulthood, it crawls out of the water onto a rock or plant stem and molts one final time. This process takes several hours or days as the dragonfly expands to its full body capacity. These newly emerged dragonflies, known at this stage as teneral adults, are soft-bodied, pale, and highly vulnerable to predators. Until their bodies fully harden they are weak flyers, making them ripe for the picking. Birds and other predators consume a significant number of young dragonflies in the first few days after their emergence.

5. Dragonflies Have Excellent Vision

Relative to other insects, dragonflies have extraordinarily keen vision that helps them detect the movement of other flying critters and avoid in-flight collisions. Thanks to two huge compound eyes, the dragonfly has nearly 360° vision and can see a wider spectrum of colors than humans. Each compound eye contains 28,000 lenses or ommatidia and a dragonfly uses about 80% of its brain to process all of the visual information it receives.

6. Dragonflies Are Masters of Flight

Dragonflies are able to move each of their four wings independently. They can flap each wing up and down, and rotate their wings forward and back on an axis. Dragonflies can move straight up or down, fly backward, stop and hover, and make hairpin turns—at full speed or in slow motion. A dragonfly can fly forward at a speed of 100 body lengths per second (up to 30 miles per hour).

7. Male Dragonflies Fight for Territory

Competition for females is fierce, leading male dragonflies to aggressively fend off other suitors. In some species, males claim and defend a territory against intrusion from other males. Skimmers, clubtails, and petaltails scout out prime egg-laying locations around ponds. Should a challenger fly into his chosen habitat, the defending male will do all he can to chase away the competition. Other kinds of dragonflies don't defend specific territories but still behave aggressively toward other males that cross their flight paths or dare to approach their perches.

8. Male Dragonflies Have Multiple Sex Organs

In nearly all insects, the male sex organs are located at the tip of the abdomen. Not so in male dragonflies. Their copulatory organs are on the underside of the abdomen, up around the second and third segments. Dragonfly sperm, however, is stored in an opening of the ninth abdominal segment. Before mating, the dragonfly has to fold his abdomen in order to transfer his sperm to his penis.

9. Some Dragonflies Migrate

A number of dragonfly species are known to migrate, either singly or en masse. As with other migratory species, dragonflies relocate to follow or find needed resources or in response to environmental changes such as impending cold weather. Green darners, for example, fly south each fall in sizeable swarms and then migrate north again in the spring. Forced to follow the rains that replenish their breeding sites, the globe skimmer—one of several species that's known to spawn in temporary freshwater pools—set a new insect world record when a biologist documented its 11,000 mile trip between India and Africa.

10. Dragonflies Thermoregulate Their Bodies

Like all insects, dragonflies are technically ectotherms ("cold-blooded"), but that doesn't mean they're at the mercy of Mother Nature to keep them warm or cool. Dragonflies that patrol (those that habitually fly back and forth) employ a rapid whirring movement of their wings to raise their body temperatures. Perching dragonflies, on the other hand, who rely on solar energy for warmth, skillfully position their bodies to maximize the surface area exposed to sunlight. Some species even use their wings as reflectors, tilting them to direct the solar radiation toward their bodies. Conversely, during hot spells, some dragonflies strategically position themselves to minimize sun exposure, using their wings to deflect sunlight.

Credit : Thought co ?

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Insects are small animals with no bones. An insect's body is protected by a hard outer covering called an exoskeleton. The body has three segments: head, thorax and abdomen. The head has eyes - which can have six to 30,000 lenses - and a pair of antennae to feel, taste and smell things. The thorax has wings and legs. The abdomen includes systems for digesting food.

The insects have proved to be the most successful arthropods. There are far more species in the class Insecta than in any other group of animals. These amazingly diverse animals have conquered all the environments on earth except for the frozen polar environments at the highest altitudes and in the immediate vicinity of active volcanoes.

Insects are the only invertebrates (animals without backbones) with wings. Much of their success results from their ability to fly and colonise new habitats. The study of insects is called entomology and entomologists are scientists who study insects.

Insects play a very important role in the web of life, in every environment. Some of their jobs include pollinating flowering plants, being a source of food for insectivorous animals and assisting in the decomposition of plants and animals.

Insect classification

Modern insect classification divides the Insecta into 29 orders, many of which have common names. Some of the more common orders are:

Mantodea - praying mantids
Blattodea - cockroaches
Isoptera - termites
Siphonaptera - fleas
Odonata - dragonflies and damselflies
Dermaptera - earwigs
Diptera - flies
Lepidoptera - butterflies and moths
Orthoptera - grasshoppers, katydids, crickets
Coleoptera - beetles
Hymenoptera - wasps, bees, ants, sawflies

Insect features

The insect body is divided into three main parts, the head, thorax and abdomen.
Insects have no internal skeleton, instead they are covered in an external shell (exoskeleton) that protects their soft internal organs.
No insect has more than three pairs of legs, except for some immature forms such as caterpillars that have prolegs. These are appendages that serve the purpose of legs.
The typical insect mouth has a pair of lower jaws (maxillae) and upper jaws (mandibles) which are designed to bite. There are many variations to this structure, as many moths and butterflies have tubular sucking mouthparts, many bugs and other blood-sucking insects have sucking stabbing mouthparts and some adult insects simply don't have functional mouthparts.
Insects have one pair of antennae located on the head
Most insects have one or two pairs of wings although some insects such as lice, fleas, bristletails and silverfish are completely wingless.

Credit : Australian.museum

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Although natural disasters and sudden changes on Earth's surface, such as earthquakes, volcanoes and wildfires, can hurt the animal kingdom, human-led changes, such as the cutting down of forests, deliberate forest fires, water and air pollution, have also severely affected wild animal habitats across the world.

Earthquakes and tsunamis

According to United States Geological Survey (USGS), each year there are 15-20 major earthquakes worldwide with a magnitude of over 7.0 and over a thousand that measure above 5.0.5 Unlike hurricanes and volcanoes, earthquakes hit without warning.6 In addition to shaking land, they can shake and displace the seabed. Islands and beaches can disappear from subsiding land or double in size because the land surrounding it is uplifted.7 When the ocean floor is displaced, it can create a tsunami, which is a series of high, fast waves that begin quickly, can cross oceans, and can last for days.8 They may be followed by landslides that bury animals alive and destroy their homes9 or floods that can sweep them away.

Volcanoes

There are at least 20 volcanoes erupting around the world at any time, not including volcanoes erupting underwater, which are much greater in number.13 Eruptions can last for months or years, spewing abrasive and toxic lava and ash, causing explosions, and heating nearby water that can boil marine animals alive.

Storms

The wind, rain, and debris from storms injure and kill animals and cause a lot of damage to their habitats, including destroying shelters and contaminating food and water sources. During Hurricane Dorian in 2019, winds reached 295 km per hour. Strong winds and rain can cause broken limbs, head trauma, as well as breathing problems and infections from getting water in the lungs. Animals are displaced and orphaned. Most of these problems would not be fatal if the animals were able to receive care, but in most cases they do not. A few lucky mammals and birds get care if they are blown into urban areas and are found disoriented on someone’s lawn.

Floods

Smaller animals are more vulnerable to drowning or dying in resulting floods and mudslides. Burrowing animals may be safe from smaller disturbances, but torrential rains can collapse their burrows or block the entrances, trapping them or leaving them without shelter. Burrow entrances can be blocked by branches, leaves, stones and other debris moved around by water or wind.

Fires

A single wildfire can kill millions of animals. The flames and smoke of forest fires kill most animals in their path, including many burrowing animals who are too near the surface, and animals who live in rivers and streams as the flames pass over. Even if they survive the fires, the aftermath can leave animals with burns, blindness, and respiratory problems that can be fatal or permanently debilitating. Hurricane force winds can carry embers and ash from a fire up to a mile away, which can trigger new fires. Strong fires generate so much energy that they change the local weather by modifying wind and temperature. The moisture coming off a fire can generate clouds that cause rain.

Credit : Animal ethics

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When one animal kills another for food, it is called predation. The animal which kills is called a predator, and the animal which gets killed is known as prey. Predators often have special skills for hunting, with highly tuned vision, hearing and sense of smell. Many have sharp claws and jaws to grab hold of and tear the body of the prey. Predators can act in a group or can kill alone. At times they hide and wait to catch their prey off-guard in an ambush killing.

Predator and prey evolve together. The prey is part of the predator's environment, and the predator dies if it does not get food, so it evolves whatever is necessary in order to eat the prey: speed, stealth, camouflage (to hide while approaching the prey), a good sense of smell, sight, or hearing (to find the prey), immunity to the prey's poison, poison (to kill the prey) the right kind of mouth parts or digestive system, etc. Likewise, the predator is part of the prey's environment, and the prey dies if it is eaten by the predator, so it evolves whatever is necessary to avoid being eaten: speed, camouflage (to hide from the predator), a good sense of smell, sight, or hearing (to detect the predator), thorns, poison (to spray when approached or bitten), etc.

In this snowy environment, the polar bear is white to avoid being noticed as it approaches the seal, and the seal pup is white to avoid being noticed by the bear.

The fastest lions are able to catch food and eat, so they survive and reproduce, and gradually, faster lions make up more and more of the population. The fastest zebras are able to escape the lions, so they survive and reproduce, and gradually, faster zebras make up more and more of the population. An important thing to realize is that as both organisms become faster to adapt to their environments, their relationship remains the same: because they are both getting faster, neither gets faster in relation to the other. This is true in all predator-prey relationships.

Another example of predator-prey evolution is that of the Galapagos tortoise. Galapagos tortoises eat the branches of the cactus plants that grow on the Galapagos islands. On one of the islands, where long-necked tortoises live, the branches are higher off the ground. On another island, where short-necked tortoises live, the branches are lower down. The cactuses, the prey, may have evolved high branches so that the tortoises, the predators, can't reach them.

Credit : New England complex system institute

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