National insect week has just finished. What? You hadn't heard of it? Ok, I must confess that I hadn't either, until Miss W was prompted to mention it last week when she made a remarkable discovery in our
wildlife pond. The pond has matured well, and is now partly covered by water lily and ringed with marsh marigold, irises, norfolk reed and many other wild plants. As a result the life inside it has proliferated too, despite the attentions of Mike, the local heron, and some of the most fascinating creatures that we see swimming about are the mini lobster-like dragonfly nymphs, fearful predators that will attack and eat almost anything smaller than they are - including other dragonfly nymphs! So, what was the discovery? Tucked under a lily leaf, about 6" above the water was this:
 |
| This is called an exuvia - nope, I didn't know that either |
It looks like an insect, doesn't it - but it isn't. It is in fact a completely empty shell, translucent and gossamer thin. No, this is what is left of one of our free swimming nymphs after it has emerged from the water to transform itself into an adult dragonfly. The problem with having an exoskeleton is that it is a fixed size, and the creature has to shed it in order to grow. This nymph will have done that several times during its couple of years in the pond. Finally it develops wing buds on the thorax, and at this stage it is ready to emerge. It climbs up out of the water, anchors itself under a leaf, and then the skin splits from the base of the head right across the thorax. You can see the opening in the picture below.
 |
| Exuvia showing emergence opening |
First the legs emerge, and an hour or so passes whist the new legs harden. Once this has happened the dragonfly wriggles and tugs until it finally pulls its body free, and the wings slip out of the wing buds. Its old casing (now called the exuvia) is completely empty, and the newly emerged dragonfly starts to inflate its wings, eyes and body to full size - about twice as long as the nymph casing from which it emerged. In our case the nymph was 45mm long, so the dragonfly will have been around 90mm - quite a big one. It's very vulnerable at this stage as it has to hang there quite still
until body and wings are fully hardened, which can take a couple of
hours.
 |
| Dragonflies mating |
I wonder what type it was? I'm no expert, but maybe some can give me a clue. Dragonflies are fantastic creatures, and the picture below is of one of our regular visitors, the rather fab Broad Bodied Chaser.
 |
| Broad Bodied Chaser by the pond |
