THE DRAGONFLIES OF HONG KONG Part I
The word dragonfly has its source in the myth that dragonflies were once dragons, both having long thin bodies and outstretched wings. Called the ‘Devil’s riding horse’in Old English, dragonflies were believed to be either demonic or seen as a poisonous winged snake. In contrast, dragonflies have been revered in Asia. Generally associated with prosperity and harmony, they are cultural symbols of good harvests and are good luck charms. (Japan’s ancient name Akitsushmia literally means “dragonfly island”).They are also farmed and eaten – both as larva and as adults – specifically in Indonesia and China.
Harmless Dragons –
They may look aggressive, with twitching moutparts and a curled sting like tale, but they are quite harmless. In many Asian countries I have seen small children catch them by the body behind the wings and then “fly” them, like brilliant miniature kites, using cotton thread tied around the thorax or legs.
If you are near enough you can hear the characteristic buzz of their flight, like a crackle of electricity. They have four wings; by moving these in a rapid figure-of-eight motion, dragonfly’s can hover like a helicopter in all six directions at up to 40 miles an hour. Dragonflies do all this while flapping their wings a mere 30 times a minute (while houseflies need to flap their wings 1000 times a minute).
Some species hold their wings open and outstretched; then at the next moment fold them shut; hence one of the classifications name of Libellula, which itself means “little book”.
Eating. Dragonflies are excellent hunters, using the basket formed by its legs to catch insects whilst flying. Amazingly they can eat food equal to its own weight in less than 30 minutes. Their prey includes mayflies, flies, mosquitoes, and other insects, even butterflies and bees.
The eyes are one of the most dramatic parts of this incredible insect. It has approximately 30,000 ommatidia within its compound eyes, and it sees in colour. Its huge many faceted bulbous eyes means it can see in all 360 degrees around it, and they say 80% of the insect’s brain power is dedicated to its sight.It also has a flattened area right in front of its eyes with a concentration of eye cells that see directly in front. This is to ensure they capture their prey whilst in fast flight.
In these two photos you can see the difference between the larrge eyes of a dragonfly (below) compared to the split eyes of a damoiselle (above right).
Inspiration for helicopters A bamboo dragonfly is an age-old Chinese toy – dating back 500BC - made up of a horizontal bar with a small hole in the middle and a straight bamboo stick inserted into the hole. Rolling the stick with both hands the bamboo dragonfly will rotate and fly into the sky, with the horizontal piece serving like a propeller. It found its way to England in the 18th Century, and fascinated and inspired the “father of aviation” Sir George Cayley, whose first project copied the design in 1796, working out the first designs for propellers. This in turn led to inspiration for Western designers working on the first helicopters.
The Dragonfly Life Cycle
A dragonfly has a life span of more than a year, but very little of that life is actually as an adult dragonfly. There are three stages of the dragonfly life cycle, the egg, the nymph, and the adult dragonfly. They will live as nymphs for up to four years, molting their skin many times, and finally when they mature into adults, they only live for a few months (depending upon the weather), often living just long enough to mature and reproduce.
Dragonfly copulation, which can
last for hours, can be seen when they are in a “wheel position”, like above, even when flying. The female curves her abdomen so her genitalia located at the tip of the abdomen can connect with the male’s penis. You may also see the pair “in tandem” where the male grasps the female behind the head, which is to deter other males, before or after mating - and it gives a nice perch for a view around, as in the picture here.
laying eggs Picture by jack
This is the Pale-spotted Emperor laying eggs.
All Damselflies and dragonflies lay their eggs in water, sometimes inside the stems and leaves of emergent or submerged plants.
Once the eggs hatch, the dragonfly larva – or nymph – is aquatic, and normally found underwaterwhile they grow and develop into dragonflies which can take one to three or four years to complete.
They are generally dull, prehistoric-looking creatures – nothing like the glorious adults. During this time the larvae will act as a voracious predator of other insect larvae, tadpoles and even small fish, even when they need a quick burst of speed, they eject water from their anal opening to act like a jet propulsion system.
Unlike butterflies, dragonflies lack a pupal stage in their development. So when the adult is ready to emerge, the larva has to crawl up onto the land, or plant stem, or tree. The shed larval skin (known as an exuvia) is left in place, and you can look for these around the artificial ponds.
Hatching during a rainy night
Freshly emerged dragonflies are ghost-like. Their wings are shiny, their bodies lacking in pigments. It can take up to two weeks for a dragonfly to reach sexual maturity, during which time there is a transition to adult coloration.
A few dragons, found near the fish ponds at the end of Bride's Pool Road, near Tai Po, New Territories.
Common Flangetail – Ictinogomphus pertinax is a common dragonfly, easily seen on top of plants or hovering along pond edges. Look for the distincitive projection near the end of its abdomen.
The Variegated Flutterer - Rhyothemisvariegata aria. With its distinct wing patterns it flies like a butterfly, and can often be seen in large groups.