Tuesday, July 28, 2009

Aeshna isoceles likes flowers of the Water Soldier

The English name is Norfolk Hawker, because in the UK the species can only be found in Norfolk. The name Green-eyed Hawker had been proposed, and that makes more sense, because the species is present in many countries outside of the UK. Aeshna isoceles is particularly common around where I live. I have spotted it several times even in city parks. But I had never seen this species ovipositing before.

Is it rare to spot oviposition of Aeshna isoceles? I did a quick check on waarneming.nl. For the Norfolk Hawker less than 1% of the observations was oviposition, as compared with more than 2% for Aeshna grandis and more than 5% for Anax imperator. So maybe it isn't very rare, but it seems to be less common.

This time I was lucky. It was at the beginning of the evening, around 18:45. Maybe the evening is a good time for oviposition, because the males are less active and so less likely to disturb the ovipositing females.

But anyway, I was there, and she was there. She picked a place for oviposition that was only 20 centimeters or so from the water side, allowing me to make this photo.

Aeshna isoceles

The most interesting part however is still to come. While I was watching this female fly around, I noticed that she was particularly interested in the flowers of the Water Soldier (Stratiotes aloides). Not the leaves, but the flowers. She was flying from flower to flower. One of the was unreachable for her, because the leaves around it left not enough space for her wings. She tried, but could not get to it. As can be seen on the photo, the flower is where she wanted to lay her eggs.

Of course this is just a single observation. I did a search on internet and found that the wikipedia article on the Norfolk Hawker shows photos of ovipostion on Water Soldier leaves. Another photo elsewhere (here) showed oviposition on a flower. And on a forum somebody said that oviposition of Aeshna isoceles on the Water Soldier isn't always, but quite often on flowers.

By the way, it is good to know that Aeshna isoceles seems strictly dependent on Water Soldier in the UK, but not elsewhere. In the Netherlands it seems to prefer Water Soldier, but does not depend on it.

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