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13 November 2012

Flying dragons ...

Broad Scarlet Crocothemis erythraea (male)





These beautiful insects belong to the order Odonata - which means "toothed ones" (Gr odontos) - because of their immensely strong mandibles.  They had been around for many millions of years and changed little in the last 300 million years.  They lived long before the pterodactyls and even birds and some of the species had a wingspan of up to 750mm (close to 1 metre).  Fossils of dragonflies show that they have changed very little over time - the Emperor Anax imperator is clearly the same species correlating with fossil specimens of 5 million years ago.

Broad Scarlet Crocothemis erythraea (female)
There are close to 6 000 species in the world - and in South Africa 158 species had been recorded.  Of these about a fifth are endemic to South Africa, meaning they live nowhere else in the world.  The species in this article shows clear sexual dimorphism - the male and female look distinctly different in colouration. The female in picture is close to the end of her life cycle with her wings showing the wear and tear of hardship clearly.  The body length of the Broad Scarlet is 39-40mm, they are medium-sized amongst their peers and the body is particularly wide.  A characteristic of the species is the small amber patch at the base of the hindwing.  They occur throughout South Africa in suitable habitat - pools ans still reaches of rivers - usually with an abundance of vegetation on the sides and floating in the water.  They perch conspicuously and flight is strong and darting.

Dragonflies live in a variety of habitats - varying from small, fast flowing mountain streams to large ponds and gardens where females may even oviposit (lay eggs) in swimming pools.  They are indicators of a healthy ecological system, as they soon disappear when water quality deteriorates or when alien vegetation invades their habitat.

It need to be fairly warm - around 20 degrees Celsius - for dragonflies to fly. The adult flying stage emerge from Spring to Autumn and the larvae spend the cooler season in the water.  

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