Dragonfly

Article, images and video by Dr Julie O'Connor, senior conservation partnerships officer, Sunshine Coast Council

If you had to design a creature that was so successful it could survive from the Jurassic era to the present day largely unchanged, what physical characteristics would you give it?

• it would need superb vision for predator avoidance and enhanced hunting skills, so you could give it large compound eyes with, say, 30,000 facets (see image “large compound eyes”)
• perhaps a highly flexible neck could complement the large eyes to give it 360º vision
• the prey it hunts might be very fast so giving the eyes a flicker-fusion rate of 300 (6 times faster than the human eye) would effectively allow it to see the world in slow motion
• you might also want to give your creature some visual dexterity, so an eye design that allows one part of the eye to detect changes in light or sudden movements, and another part to track fast-moving prey would be ideal
• it would also be beneficial to be highly manoeuvrable, so an ability to turn within its own body length would be handy, as would the possession of two pairs of large wings that could beat either together or independently (see image “wings can function independently”)
• speed would also be important so you might want to give it large wing muscles that will allow your creature to fly at speeds of up to 65km hour.

If you incorporated all the above in your design, congratulations, you have just designed a dragonfly, one of the planet’s extraordinary examples of the way evolutionary strategies shape life on earth.

The fact that some Australian dragonfly species were here when Australia was part of the larger Gondwana landmass is testament to the phenomenal success of these physical attributes.

Dragonflies are not only exceptional aerial predators as adults, but they are also formidable in their aquatic larval stages. Some species use ‘sit and wait’ ambush tactics while others pursue and attack. They are powerful enough to capture small fish and tadpoles and other prey items larger than themselves.

The tiny wing buds, which eventually become the full adult wings, are present on the nymph immediately after hatching and will become progressively larger with each moult. Depending on the species and conditions, dragonfly larvae progress through 9-15 moults before reaching their full adult form.

When the larva is fully developed with fully formed wing pads, it will leave the water to crawl onto a plant or rock to prepare for the emergence of the new adult dragonfly (see "dragonfly exuvia" image). To avoid predators this is usually done under cover of darkness. While it stays in that position it gradually swells its body until the exoskeleton splits along the head region and thorax.

After the dragonfly has dragged itself free of its final larval exoskeleton, known as the exuvia, it will gradually inflate its new body and wing buds by pumping haemolymph through its veins until the crumpled wings expand to the exquisite wings we see on the adult dragonfly (see video).

That extraordinary metamorphosis has long captured the human imagination. Dragonflies feature in folklore and mythology in many cultures across the globe, and in 1833 Alfred Lord Tennyson penned The Dragon-Fly:

Today I saw the dragon-fly

Come from wells where he did lie.

An inner impulse rent the veil

Of his old husk: from head to tail

Came out clear plates of sapphire mail.

He dried his wings: like gauze they grew;

Thro’ crofts and pastures wet with dew

A living flash of light he flew.

Glossary

• haemolymph – a fluid equivalent to blood in most invertebrates.

References

• Attenborough, D. 2006. Life in the Undergrowth, Princeton University Press
• Brunet, B. 2000. Australian Insects: A natural history, New Holland, Sydney
• Theischinger, G & Hawking, J. 2006. The Complete Field Guide to Dragonflies of Australia, CSIRO Publishing, Australia.