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Radley Lakes Wetland Centre Activities and Events in 2011 (July)

   
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On this occasion, as a relief from hard labour, and perhaps as a reward for it, volunteers were treated to a guided walk in search of damselflies and dragonflies led by local ecologist, Ian Smith. While the weather was not ideal for seeing lots of dragonflies on the wing, with the day starting cloudy and a little breezy, there was still plenty to see and learn.
 

Dragonflies and damselflies spend most of their lives in the water as larvae and emerge into adults during the summer months. This involves the insect climbing out of the water, often along a plant stem. It then has toextract itself from the larval case, unfold its wings and warm itself up before it can fly off. During this process, which can take several hours, the insect is vulnerable to predators, mainly waterfowl, such as ducks and coots, foraging on the surface of the water. Different species have evolved various strategies to minimise the risk. The larger dragonflies emerge at night, while damselflies, which generally emerge during the day, climb up as far as possible out of the water so they are above the easy reach of waterfowl foraging at the water’s edge. The larval cases, known as exuviae, that are left behind are therefore good evidence of dragonflies and damselflies breeding in the water.

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Exuvia of Emperor Dragonfly (Anax imperator) recovered from northern edge of Thrupp Lake.

 

Much of the morning was spent looking for and collecting exuviae along the northern shore of Thrupp Lake. These were mainly of the emperor dragonfly, Anax imperator, the UK’s largest dragonfly, and one which is often seen in flight around the lakes.

   
 
There were also coenagrionid damselflies (common blue and blue-tailed damselflies) emerging on the wooden structure of the bridge across the NW corner of Thrupp Lake. One was found just beginning to emerge from its case, and this was recorded for the first 5 minutes before we had to move on.
 
Emergence of a damselfly

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1m 14s

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2m 25s

 
 

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4m 39s

The wings, which are rolled up into four finger-like tubes are now clearly visible.

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5m 44s

This shows how the damselfly extracts itself fom the case. The case is broken across the back along base of the thorax and the front part pushed forward creating a hole large enough for the adult to emerge through. The head is pulled out first, then the tail. Afterwards, the empty case springs shut leaving one wondering how anything that was ever inside could have got out.

 
 

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Newly emerged blue-tailed damselfly (Ischnura elegans) resting on wooden handrail

 

 
The weather was gradually improving and the sun began to peek through the clouds. While walking along the western shore of the lake, we encountered both Common Blue (Enallagma cyathigerum) and Azure (Coenagrion puella) damselflies among the lakeside vegetation. A large Red-eyed damselflied posed on a sprig of vegetation some distance out over the lake just in front of the bird hide.
 

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Red-eyed Damselfly (Erythromma najas)
posing on a sprig of vegetation over the lake.

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Common Blue Damselflies (Enallagma cyathigerum)
in mating embrace.

   
 

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A male Common Blue damselfly (Enallagma cyathigerum).
This is distinguished from several similar-looking species
by the shape of the black mark between the first two abdominal segments.

 

The walk proceeded to Orchard Lake to the south. This is one of Radley’s most spectacular ‘lakes’ and is an excellent site for many species of wildlife, including dragonflies. Here our guide netted an adult Emperor (Anax imperator) and showed us how to handle it by its wings without harming it. In this way, it was possible to obtain some spectacular closeup shots of this amazing insect before eventually releasing it unharmed.

 

Three hours having elapsed, it was time to return to Sandles for a welcome cup of tea and some biscuits.

 
 

Table of damselflies and dragonflies recorded on the day

Scientific name(Click on name to see image) Common Name Observation
Aeshna mixta Migrant Hawker exuviae
Anax Imperator Emperor adults & exuvia
Coenagrion puella Azure Damseffly adults
Enallagma cyathigerum Common Blue Damselfly adults & exuviae
Erythromma najas Red-eyed Damselfly emerging and adults
Ischnura elegans Blue-tailed Damselfly emerging and adults
Orthetrum cancellatum Black-tailed Skimmer exuviae
Sympetrum sanguineum Ruddy Darter adults
Sympetrum striolatum Common Darter exuviae
 
 
Other species recorded:
 

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Brookweed (Samolus valerandi) a rare plant growing by Orchard Lake 

Flora

Field Madder (Sherardia arvensis)

New Zealand Pygmyweed (Crassula helmsii)

Brookweed (Samolus valerandi)

Fauna

Mystacides longicornis – a caddis fly

Cicadella viridis – a leafhopper

Pardosa amentata – a wolf spider

Small Skipper (Thymelicus sylvestris)

Common Soldier Beetle (Rhagoncha fulva)

Shaded broad-bar (Scotopteryx chenopodiata)

plus a few as-yet unidentified things.

 

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A blue/green leafhopper (Cicadella viridis) poses for a photograph.

   
 

Permanent link to this article: http://www.radleyvillage.org.uk/radley-lakes-wetland-centre-activities-and-events-in-2011-july/