Among the 51 species recorded, the Midget (Mortonagrion hirosei) is a damselfly classified as 'endangered' by the World Conservation Union, while 15 others are rare or uncommon species in Hong Kong.

The Midget has only been found in a few places in Hong Kong and Japan.

Also, the researchers found the Eastern Lilysquatter (Paracercion melanotum) in Mai Po for the first time. It is a blue damselfly - about 25 millimetres long - that is very rare.

WWF Hong Kong education officer Alex Wong Wai-tung said dragonflies and damselflies are semi-aquatic insects developed from larvae.

Dragonflies spend their early stages in fresh water, and therefore an aquatic environment, such as marshes and ponds, is vital in their breeding cycles.

He also pointed out a crucial difference between a motionless dragonfly and damselfly - the former spreads its wings halfway while the latter keeps still.

Since the 51 species comprise more than 40 per cent of all types of dragonfly and damselfly ever recorded in Hong Kong, the study shows that Mai Po provides a key food source and breeding ground for the insects.

But WWF Hong Kong said freshwater habitats in Hong Kong are threatened by pollution, reclamation and the invasion of exotic species.

These have had a negative impact on dragonflies as well, the green group said.

'The more we understand their [dragonflies'] ecology, the better we can work out a strategy or habitat management. Apart from their ecological value, dragonflies also serve as an indicator of the integrity of our natural environment and are a key component in our education programme for students,' said WWF Hong Kong training officer Samson So.