Sunday, 22 September 2013

Zygonyx iris and Zygonyx asahina

Zygonyx iris is a common species of moderate to fast streams with rivulets in semi-open terrain. I encountered it for instance at Tam Dao National Park, where it is common in the lower reaches of the streams, and in Ba Be National Park. It tends to fly rather high, also when patrolling it is not very close to the water, but rather a few meters up. To my surprise I encountered in the interior of the forest at Tam Dao libellulids that superficially looked like fresh Z. iris, but had strikingly yellow S1-3. These patrolled smaller rapids and waterfalls inside the forest, close to the water, and instead of making long steady patrol flights, would hover in the same position for prolonged periods. What was more, Z. iris was not encountered this deep into the forest. In August I was first able to catch and photograph a male in hand, and later a female. This proved the give away, with the large amber basal patches to the wings this could be nothing else but Z. asahina, a species until now only verified on the border with China in the extreme north of Vietnam. Subsequent research confirmed this.

Zygonyx asahina, female

Zygonyx asahina, male

Zygonyx iris, male, for comparison
Note the lack of dorsal markings in Z. asahina on S4-10 and the very extensive yellow on S1-3. On top of this, the anterior lamina has a different shape, in Z. iris it has a bend towards the front.

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