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Sunday, 21 September 2014

Willow Emerald Damselfly has reached Rainham Marshes

Five years since it was first discovered in Suffolk, the Willow Emerald Damselfly (Chalcolestes viridis) has been seen at RSPB Rainham Marshes.

A few weeks ago, a regular visitor, Dawn Cowan, took some pictures of an Emerald damselfly at the bridge in the Woodland. I thought that it was probably an immature Lestes sponsa, but after some discussion and close study of her images, the conclusion was that it was indeed C. viridis.
Then, 2 weeks ago, Tony Madgwick and I spent a day looking for and at suitable habitat in the hope of finding another one. We were about to pack up for the day when, next to the Cordite Store, we disturbed a large damselfly which then flew up into a tree. We got binoculars on it for only a very few seconds before it flew off, but we were pretty confident that it was a C. viridis.


On the same day, another visitor, Mark Philips, took a photograph of what was clearly a male C. viridis at the "Troll Bridge" . This is the where the boardwalk to the west of the Woodland does a zigzag across a ditch - between the Bog Wood and the Ken Barrett Hide.

The Thursday after that, encouraged by Mark's image, I spent some time at the Troll Bridge. I didn't see any damselflies, but I did discover some marks on a branch of the overhanging willow tree that I suspected were the galls that the tree produces when a Willow Emerald has laid eggs into it's bark. I consulted Tony and other experts at the BDS who confirmed that they were C. viridis ovipisition galls, and also suggested that they may be from last year!

Last Tuesday, I went back to the bridge hoping to shoot some video, and I finally managed to see a damselfly properly for myself. A male was perching on Burr-reed, quite unconcerned about me and several others watching. After about half an hour, two more - a male and a female in tandem - appeared. They flitted back and forth across the little ditch from the burr-reed to the willow tree, and even spent some time laying eggs into at least one twig of the tree.


Another female was seen close to the Purfleet hide on Thursday, and many people are still seeing the action at the Troll Bridge.

Willow Emerald is the only damselfly in Britain to lay eggs into the branches of trees - in particular trees which overhang water. It spends the winter as the egg, protected under the tree bark, and the prolarva then emerges in spring and drops from the branch into the water below. The larva develops over a period of just a few months, and the adult emerges towards the end of summer.

While we haven't yet found conclusive evidence of breeding at Rainham Marshes (only an exuvia or emerging adult would provide that), the appearance of oviposition galls and an ovipositing female is a good sign. It seems very likely that Willow Emerald is at Rainham Marshes to stay.

Saturday, 20 September 2014

Tall Ships passing Rainham Marshes after the Greenwich Festival

On the afternoon of 9th September, the Thames river wall at Rainham Marshes was full of people gathered to watch the Tall Ships pass as they headed out to sea after the grand finale to the Royal Greenwich Tall Ships Festival.

I equipped my camera with a wide-angle zoom lens and set up on a tripod. Through the afternoon I moved to various spots along the path to shoot some images for this timelapse.
I took a shot every 3 seconds, and ended up with a total of about 1800 images. I adjusted the exposure in Lightroom, then exported to 1920 x 1080 pixel jpegs. I used Quicktime to build a video clip for each different view and then Premiere Elements to edit together the video and add titles.
I've discovered since that Premiere Elements can import still sequences directly, so I can save the Quicktime step for my next timelapse.