The are the only invertebrate capable of

The evolution of dragonflies can be traced back more than 300 million years, predating dinosaurs by almost 100 million years (Corbet, 2013). Dragonflies were one of the first winged insects on the planet and are one of the oldest insects to still exist. Surprisingly, dragonflies have not changed significantly from their ancestors. ( Zielinski, 2011 ) They are classified as a part of the Arthropoda phylum – the largest phylum in the animal kingdom ( Barnes, 2017 ). Dragonflies are the only invertebrate capable of flight and can be found in almost every habitat and exist on every continent except Antarctica (Corbet, 2013). Adult dragonflies have segmented bodies, made up of a head, thorax, and a 10 segment abdomen. They have a hard exoskeleton that supports and provides protection to the dragonfly. As well as their exoskeleton combined with the muscle system helps with locomotion. They have six legs all located near their head, mainly used for laying eggs and hunting. They have two mostly transparent narrow wings with a wingspan of up to 16cm. ( Barnes, 2017 ) Their hind wings are much broader and larger than their forewings, and contain veins which add strength and flexibility to them. Unique among insects, dragonflies can use their fore and hind wings separately. This enables them to hover when flying, as well as move in all directions, and turn quickly. The speed they can fly is around 100 body lengths per second forward, 3 body lengths per second backward, and hover for approximately 1 minute. (Waggoner, 2000) Their wings also remain extended vertically when they are resting because they do not have hinges. Finally, an especially useful feature they have is two large compound eyes that cover most of their heads and allow them to see all around themselves. Their eyes have about 30,000 lenses giving them almost a 360-degree field of vision. This is advantageous for hunting prey. They can be a wide variety of colours ranging from metallics to pastels. ( Britannica, 2017 )When it comes to food, dragonflies are generalists and eat whatever is suitable, abundant and in their region. This consists mostly of insects including termites, ants, mayflies, mosquitoes, and caddisflies. The dragonflies that hunt the most are females developing eggs, and maturing larvae. However, temperature as a huge effect on there hunting. Dragonflies will only hunt when it is warm. This is because their wings need to be a certain temperature to function. If they are too cold the dragonfly will find a way to heat them up, commonly by staying in the sunlight. ( Britannica, 2017 )  Prey is captured by their labium which is shot forward quickly to grasp prey and then is pulled back towards its mouth to be chewed. The labium is located beneath their jaw and acts like a pair of hands with thorns on the end ( see figure ___). ( Trueman and Rowe, 2009 )  Most dragonflies will either use a sit and wait strategy to hunt, or will stalk their prey. Their mouths have also adapted for biting to make them efficient hunters. Other adaptations enable them to avoid predation as well as hunt prey, including exceptional visual responses and agile flight. More than 80% of their brain is used to analyze visual information and they have complex colour vision.  Their predators include birds, lizards, frogs, spiders, fish, water bugs, and even larger dragonflies. (Waggoner, 2000)Dragonflies are believed to belong to the order of Odonata which include some of the largest flying invertebrates to ever exist (Waggoner, 2000). Odonata is an order of aquatic paleopterous insects and means “toothed one”  referring to their serrated teeth ( Trueman and Rowe, 2009). Over 5,000 known species of dragonflies (including Damselflies) belong to the order of Odonata (Zielinski, 2011). Each of those species has evolved to have different appearances and jobs in order to fill different niches and avoid competition between species (British Dragonfly Society, n.d). Odonates have many distinguishing characteristics including, minute antennae, very large eyes, 2 pairs of transparent wings with small veins, a long slender abdomen, aquatic larval stage (nymph) with tracheal gills, and labium (Waggoner, 2000). The system of the head of Odonata is unique among arthropods and consist of a head and neck. The order of Odonata has 3 suborders, dragonflies are included in the Anisoptera suborder. One of the oldest ancestors with recognizable fossils is the extinct order Protodonata (see figure ____). They were similar to dragonflies in which they were fast flying and had spiny legs. Although, they were much longer with wingspans up to 75 cm and were thought to have existed at the same time as dinosaurs. (Waggoner, 2000) Protodonata fossils show solid evidence that links them to existing odonates. This includes an aquatic larval stage, a complex life cycle, and their mating system which involves the transfer of sperm. (Bybee et al, 2016)Dragonflies are commonly compared and difficult to decipher from Damselflies. Damselflies are even often referred to as dragonflies. They fall under the order of Odonata as well except being in a separate suborder called Zygoptera. Damselflies, however, have well-separated eyes, evenly sized wings, and can rest their wings horizontally unlike dragonflies who have to leave them vertically. (Britannica, 1999) Another difference is the shape of their labia. In damselflies, the labium is flattened whereas dragonflies have a spoon-like shaped labium (British Dragonfly Society, n.d).The lifecycle of all dragonflies includes 3 stages, it begins as an egg, then nymph, then adult (see figure ____).  Dragonfly eggs are round and approximately 0.5mm long. They are generally laid on, above, or below water. They can take  7 – 9 days to hatch or even several months depending on the species. (Trueman and Rowe, 2009) Most of a dragonflies life is spent in the larval stage which traditionally lasts 1 – 2 years but can go up to 6 years depending on its surroundings. (Waggoner, 2000) Nymphs are usually found in still water or slow flowing rivers and streams. They will eat anything from other larvae their size to tadpoles and worms. (Britannica, 2017) As a nymph, they have six legs, wing-sheaths (visible halfway through development), a labium, and are capable of breathing underwater (British Dragonfly Society, n.d). To do so, they have gills in their rear abdomen that expand and contract for gas exchange to occur. Their gills also allow them to move by exerting short bursts of air for jet propulsion which is useful to escape predators. Dragonflies are in fact capable of growing back limbs in the case of losing one. This can happen after each molt. In the larval stage, a dragonfly will molt 6 – 15 times. In its final molt, they crawl out of the water typically on a plant stem and become an adult dragonfly with functional shiny wings (Waggoner, 2000). During this molt they pull their top body segments out then have to wait around 30 mins for their legs to harden so they can continue. Once completely out of there shell, the adult is about double the length of its exuvia (larvae shell) This process lasts approximately 3 hours. They are a pale green colour with hints of their final colour at first, allowing them to partially blend into their surrounding (see figure ____). (British Dragonfly Society, n.d)  For the first few days of being an adult, they will feed and fully develop their colour (Trueman and Rowe, 2009). They molt due to the fact that exoskeletons do not grow so they must shed the old one in order to grow a new one. Dragonflies were the first to develop hemimetabolous development, an incomplete form of metamorphosis where there is no pupal stage ( Waggoner, 2000 ). The adult stage lasts less than a month up to six months.Male sex organs are located on their abdomen near the second and third segment. Sperm, on the other hand, is stored in an opening on the ninth segment of the abdomen. Therefore the male must transfer the sperm prior to mating. Mating happens in tandem flight or perched. The male holds the female by her head while flying. (Trueman and Rowe, 2009) The skeletal muscle and arrester immobilize the head during feeding and mating. This is considered to be an adaptation to support the head during tandem flight. ( Gorb, 1999 ) The mating process commonly last for 1 – 2 minutes although some species will mate for several hours.Dragonflies must mate with the same species since their sex organs are very intricate and species-specific (Corbet, 2013). Males take the mating process seriously and are very territorial. They will defend and fight other males who try to invade their mating area and possibly injure them. The females will then mate with the best fighters. If the female decides to mate with the male, he will clasp her head and she will bring her abdomen towards his. He will then transfer his sperm into the female creating a heart-shaped “wheel” formation (see figure ___). (Corbet, 2013) During this, he may also use a hook-like structure located on his penis to scoop out any sperm that is already in her from other males. Once the process is over, the female typically will lay her eggs immediately. The male will decide whether to leave the female or follow her around to ensure no other males remove his sperm and her eggs are laid (Trueman and Rowe, 2009). They continue to reproduce with whomever until death.All species of dragonflies are completely harmless to humans because they cannot sting or bite. One benefit they provide to humans is that they assist in the control of pest insects potentially eliminating health risks. This includes nuisance insects like biting flies and mosquitoes that might carry diseases ( Trueman and Rowe, 2009 ). For some inland fishermen, dragonfly larvae can be used as bait. Additionally, in certain countries, they are eaten by humans. Another benefit dragonflies provide is that they aid in assessing the effects of climate change and global warming ( The Xerces Society for Invertebrate Conservation, n.d ). The presence of dragonflies helps in indicating and determining the quality and health of an ecosystem ( Trueman and Rowe, 2009 ). Since most of their lives are spent underwater, they require clean water to survive so their presence can tell humans the water quality. Healthy vegetation is also a must for survival, therefore, the absence of dragonflies could potentially mean there are pesticides and excessive nutrients, heavy metals, or various water contaminants from humans. Water quality issues are having a negative impact on the dragonflies and putting them at risk. ( Simon, 2012 )