Dragonflies are 20 mm - 150 mm in length.They have two pairs of membranous wings, clear and similar in length. Both pairs have numerous cross-veins forming many cells. At rest they hold all four wings outstretched. The body is widest at the wing attachment with a slim abdomen that appears soft and fragile with two short tails (cerci).The tails are sometimes used as claspers in males which are used to hold onto the females during mating.Antennae are short and hair-like.Eyes are large and bulging, nearly touching in the middle.Mouthparts are designed for chewing or munching.They have six legs, short with strong bristles with the fore and midlegs held out from the body and bent at the elbows.Males are often found near water perched on vegetation, rocks or in the air.Females may be found away from the water.Dragonflies are solitary, though it is not uncommon to see large numbers perched on structures like fences.They are extremely strong fliers, capable of high speeds and flight in all directions, can hover, move in zigzags, and even fly backwards. .Males tend to be territorial.They are all predators that prey primarily on flying insects, taken from the air or as they land on vegetation.They are mostly active during the day, though some are primarily active around twilight and few are active at night.One species that lived around 250 million years ago was the largest insect known to exist and had a wingspan of over 70 cm. Their success as a group is largely because of their fantastic flying abilities and their well-developed eyes. They are excellent hunters of other flying insects. Many people find them intimidating but, despite their powerful jaws, they are harmless. In fact, they do us a favour by eating many insects that bite us.Eggs are laid into, or close to, water. The larvae are usually aquatic, feeding on other insects, tadpoles and occasionally fish. After progressing through up to twelve larval stages the larvae crawl out of the water. Their skin splits and the adults emerge. The adult stage has a pre-reproductive period that may last up to three weeks. At this stage the colour of the wings and body may change.There are over 6,000 species worldwide, 320 species known from Australia and about 100 of these occur around Sydney. The Asiatic Blood Tail, Lathrecista asiatica, is a species of dragonfly occurring in a widespread area from India to Australia.