Pets: Why we’re falling for the low-rise dachshund
Dr Ben Aldiss looks at the remarkable life of these airborne predators
Having combed the undergrowth for caterpillars in last month’s look at Norfolk’s nature, we’re still hunting insects in September. This time it’s D for Dragonflies and I’m predicting an abundance of them around then. I say ‘predicting’ because I’m writing this a full six weeks early to meet the necessary publishing deadlines. If we continue to experience the wonderful summer weather I’m looking at through my office window, then the season of many insects – including dragonflies – will be extended and their numbers will increase as well.
Dragonflies received their name at least 400 years ago and it aptly describes the behaviour of the larger ones as they dash through the air on their strong wings in search of prey. We have around 25 species in Norfolk, a number of which are still on the wing in September.
The smaller varieties may look less impressive at first glance, but their colours can be equally stunning, if not more so. These smaller ones are the familiar damselflies, including the common Azure Damselfly with its bright blue abdomen and a particularly jewel-like creature called the Banded Demoiselle, the male of which is unmistakeable as he dances up and down over the water in his
livery of iridescent ultramarine with dusky patches on each of his four wings.
Not only are damselflies smaller than their huge cousins, but they differ in their weak, fluttering flight, their relatively small eyes and the way they hold their wings at rest: folded parallel to their bodies as opposed to stretched out flat at right angles.
I’m going to write about other Norfolk specialities under the letter N, but one should logically be included here – the Norfolk Hawker Dragonfly. This impressive creature is large and quite colourful, being mainly a light tan colour with yellow markings and enormous green eyes. If you were lucky, you might have seen one during its relatively short season in June and July, hunting around its favoured habitat in and around the Broads.
Norfolk Hawkers – like all dragonflies and damselflies – are carnivores, but the female of this species seems to depend on a rare plant, the water soldier, in which to lay her eggs.
The eggs of dragonflies and damselflies hatch into nymphs, but butterflies and most other insects produce larvae, the difference being that nymphs resemble miniature adults, whereas larvae are completely unlike their parents (just think of a butterfly caterpillar or fly maggot). Dragonflies share this feature of their life cycle with grasshoppers and cockroaches – a young grasshopper looks like a tiny version of the adult.
Dragonfly and damselfly nymphs have six legs and big eyes, but only develop wings when they emerge from the water and crawl out of their final skin to become an adult. The smaller damselflies spend a year or less as nymphs, changing their skins only a few times as they grow.
The Norfolk Hawker and other dragonflies though, have to undergo this ecdysis, as it’s properly called, around 15 times over the course of the two or three years they spend under the water. When nearing maturity, dragonfly nymphs are big, fearsome-looking beasts, but even then they rely on camouflage to avoid becoming fish-food and also so they can creep up on their prey.
The Norfolk Hawker nymph is predominantly pale brown with darker speckles, allowing it to blend in very effectively against the muddy bottom of the pond or broad. It will eat any small creature it can catch, including tadpoles and young frogs.
Considering the impressive speed of its parents in flight, the nymph is a very sluggish creature, so it would seem to have trouble capturing its prey, or escaping predators. However, it has two remarkable adaptations.
If it needs to escape, it can use a form of jet-propulsion by squirting water forcibly out of its back end, sending it shooting forwards out of danger. Then, if it’s hungry, it has another astonishing trick. Creeping up slowly to within a couple of centimetres of its prey, it suddenly shoots out a telescopic, hinged jaw from beneath its head.
Called a mask, this useful attachment has two claws on the end that grip the unfortunate prey before dragging it quickly back to the mouth. Damselfly nymphs also have this feature for capturing prey, but instead of the jet-propulsion apparatus, they carry three leaf-like gills at the end of the abdomen and escape predators by sinuous movements of their bodies, using their gills like the fins of a fish to propel them through the water.
When ready to emerge as an adult, the nymph crawls up a plant stem out of the water that’s been its home for so many months, then emerges as a winged dragonfly or damselfly a few hours later by splitting its final nymphal skin. Unlike other insects, though, adult dragonflies don’t develop their final colours until up to a fortnight after emerging and will spend most of this time hunting some considerable distance from their pond, before returning, resplendent in their dazzling livery to hunt over the water where they spent their youth.
The Norfolk Hawker will eat any small creature it can catch, including tadpoles and young frogs
ABOVE: A Norfolk hawker dragonfly at Upton Fen
ABOVE: Demoiselle by the river Yare at Bawburgh