Sunday, 17 June 2012

Fascinating behaviour of Green Metalwing (Neurobasis chinensis)

I wrote about my recent trip to Endau Rompin in my previous blog (posted on 10 June 2012). During the trip I recorded on video interesting behaviour of a few nice species of forest stream. Let me talk about that of a Neurobasis species today.

Species of Neurobasis are known as 'Metalwings', on account of the brilliant iridescence of their coloured wings. They are damselflies and engage in elaborate territorial fight and courtship during which the male displays brilliatly coloured wings, a performance which always leaves the observer breathless with admiration. The late M.A. Lieftinck spoke for many when he called Metalwings the "Birds of Paradise among Odonata."

In Singapore, only one species of metalwings had ever existed - Neurobasis chinensis (Green Metalwing). The last individual of Neurobasis chinensis was seen in a stream in the Upper MacRitchie Basin in 1970. Now, this species is considered to be nationally extinct. All suitable habitats for this species (clear, moderately flowing streams) have been destroyed in Singapore.

The footage of Neurobasis chinensis below was recorded in Malaysia in June 2012. It shows the patrol flight of a male, followed by vigorous territorial fight between two males. A female then came to the scene and the winning male copulated with her. I couldn't follow the mating pair with my camera as they flew to a concealed position in the vegetation. When they returned, they flew separately, with the male flying very low, just above water. The tips of his hindwings occassionally touched the fast flowing water, as if to test the flow rate. His abdomen was uplifted, apparently displaying the small white spot beneath. The female followed him closely behind, occasionally touching the flowing water with the tips of her legs, as if to test the flow rate too. The male eventually landed, perched on an oviposition substrate with his abdomen tip still turned upward. The female landed behind him and soon started to oviposit by curling her abdomen into a semi-circle and dipping the tip into water. Her male guarded her responsibly. At times, the male flew further from his mate and perch on a leaf nearby.

The other male (the one who lost the battle to the winning male earlier) came back and challenged the winning male again. The winning male took on the challenge and the two males flew in a tight circle just above the ovipositing female. The loser lost again and flew away. The female continued to oviposit without being harassed by the intruder.

It is amazing how such a delicate insect can stand against the swift current while ovipositing. A few times I thought she would be washed away by the strong current, but she could almost always hold onto the water plants. When she did lose grasp, she simply flew up and landed again.

For a more detailed account of the behaviour of Neurobasis chinensis, please refer to this book:

The Metalwing Demoiselles of the Eastern Tropics by Albert G. Orr and Matti Hämäläinen.

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