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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. |
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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.
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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.
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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. |
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Emergence
of a damselfly |
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
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| 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.
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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. |
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Three
hours having elapsed, it was time to return to Sandles
for a welcome cup of tea and some biscuits.
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Table
of damselflies and dragonflies recorded on the day
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Other
species recorded: |
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Brookweed
(Samolus valerandi) a rare plant growing by Orchard
Lake
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A blue/green
leafhopper (Cicadella viridis) poses for
a photograph.
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