Dragonflies abound

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by Kate C
Publish date
9 March 2011
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Last weekend's balmy evenings brought out a squadron of deadly aerial hunters in my backyard. I saw about ten dragonflies zooming around, plucking flying insects from the sky. It was an amazing sight – I’ve never seen so many in action in such a small area. From the half-eaten bodies I saw on the ground, it seems they were feasting on a swarm of young ant queens and males on their nuptial flights.

Dragonflies and damselflies belong to the 300-million-year-old insect order Odonata. You can tell the difference between the adults easily; damselflies are generally smaller, more delicate, and hold their wings together above their body when resting. Dragonflies are their beefy relatives and most rest with their wings held out to each side. As juveniles, odonates – known as nymphs – mostly lurk in freshwater ponds and streams eating smaller creatures such as mosquito larvae and small crustaceans.

Dragonfly eyes Compound eyes of a dragonfly.
Source: Museum Victoria
 

Adult dragonflies have incredible eyesight thanks to large compound eyes that wrap almost all the way around their heads. Combined with extraordinary agility, they are skilled hunters and snatch gnats, moths and flies from the air, eating them on the wing with their powerful jaws. They even mate on the wing; the male guards the female while she lays eggs in the water, grasping just behind her head with the claspers at the end of his abdomen.

dragonflies laying eggs in a pond A pair of dragonflies laying eggs in a pond. The male is holding on to the female just behind her head as she dips her tail into the water to lay eggs.
Image: Susan McBratney
Source: Susan McBratney
 

I love watching these animals and their amazing behaviour, which is reflected in the common names for some dragonfly families – hawkers, cruisers, skimmers and perchers. Another common name, darner, harks back to a medieval folk tale that they were the devil’s darning needles that would sew shut the mouths of unruly children!

Male scarlet darter (Crocothemis erythraea) male. Male scarlet darter (Crocothemis erythraea) male on the island of Crete. The thorax of the dragonfly is packed with powerful muscles that drive their wings. Unlike most other insects, dragonflies and damselflies can move each pair of wings independently of the other.
Image: Stavros Markopoulos
Source: Used under Creative Commons license CC BY-NC 2.0 from macropoulos
 

A lot of people have mentioned seeing more dragonflies than usual this season so I had a chat to MV’s aquatic insect expert, Richard Marchant, to find out more. He says that knowledge of Australian dragonfly biology is patchy, but they’re quite long-lived – nymphs might take one or two years to reach adulthood, and adults probably live a month or more and travel many kilometres. He believes that all the rain Victoria has received this summer means the increased areas of standing water has attracted dragonflies in huge numbers to many parts of the state, including the greater Melbourne area. So look up, and enjoy the stuntwork of these acrobats in the summer sky!

Links:

Infosheet: Dragonflies and damselfies

Australian Museum: Order Odonata

Devil's Darning Needle

600 Million Years: Giant invertebrates in the Carboniferous

Herald Sun: 'Bugs galore as Vic gets steamy'

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