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In this season of dengue and other mosquito-borne diseases, why dragonflies matter

One of Nature’s unparalleled masterpieces, dragonflies are a marvel of design and engineering

Ranjit LalA dragonfly (Credit: Ranjit Lal)

August, I believe, was celebrated as “Dragonfly Month” and all through it, I scanned the skies around my neck of the woods for the squadrons of these breathtaking glittering insects, launching hunting sorties after flies, butterflies and even other dragonflies, as well as patrolling and ferociously protecting their own airspace. The skies, alas, remained empty and I began to wonder if this had anything to do with the near total absence of rains in Delhi during that month. Dragonfly nymphs (not nymph-like by any stretch of the imagination) prowl underwater for a year or more, snatching tadpoles, small fishes and other underwater dwellers before finally hauling themselves out via plant stalks and morphing into the gorgeously tinted insects that we know. They live for a far shorter time as aerial hunters than they do underwater. Was it possible that a large number of dragonfly nymphs, that hatched perhaps last year, and prowled the depths since, simply died off because their ponds and water bodes dried up due to the lack of rain, leading to a lack of food?

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To confirm my suspicion, I rang my friend Faiyaz Khudsar at the Yamuna Biodiversity Park. He told me that they were carrying out a survey of dragonflies and damselflies – and the results of that survey did indeed indicate that fewer species and numbers were being recorded. But it was not — as I had suspected — because all the water-bodies which the nymphs inhabited had gone bone dry, but because the higher temperatures and dropping water level, speeded up the metamorphosis of the nymph, causing it to morph prematurely into adulthood. One result of this was smaller (and presumably weaker) wings, which inhibited the ability of dragonflies to disperse widely. That, perhaps, is one reason why I haven’t seen them in my neighbourhood, which is not exactly cheek-by-jowl with a water body (The Yamuna is about 2 km away as the crow flies).The explanation makes perfect sense: in the temperate regions, where the water is much colder, dragonfly nymphs can remain underwater for as many as five years before launching themselves off, developing slowly into adults.

Why should we now be bothered about the absence or presence of dragonflies and damselflies? They are after all, just another kind of insect – and there are millions of other creepy crawlies around. Well, we’re beginning to hyperventilate over dengue nowadays (hopefully COVID-19 has had its day) and better than any pesticide spray for mosquito control are dragonfly nymphs, which apparently feast voraciously on mosquito larvae, as do adult dragonflies on adult mosquitoes. But if you are a dragonfly with small, underpowered wings, you can fly only shorter distances and have a smaller hunting range, making life easier for mosquitoes.

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The presence or absence of dragonflies over a water body is also an indication of the level of pollution. Some dragonflies and damselflies can tolerate relatively dirty water, others prefer clean water to lay their eggs in (usually stuck to underwater stalks or the under-side of leaves) and by knowing their preferences, we can infer the state of the water. With the monsoon playing catch-up in September, the dragonflies and damselflies, too, have got busy laying their eggs. But with winter approaching, what’s going to happen to those eggs, Faiyaz asks. Will they hatch at all? If they do, the nymphs will certainly have to “over-winter” before thinking of emerging as combat flying machines next summer.

These apart, we need to be bothered about their fate because dragonflies and damselflies are among Mother Nature’s masterpieces of design and engineering. It is thought they evolved some 300 million years ago, with their design remaining virtually unchanged for the last 150 million years. They were whoppers, dragonfly fossils having wingspans of 7 feet have been found buried in coal seams in France.
They have among the best eyes in the insect world with around 30,000 lenses in each globular eye, some of which track movement, others which make out shapes. Their bulbous heads move every which way, their front legs are barbed baskets in which prey is scooped up and consumed on the wing; the cellophane-like wings (so beautifully tinted) can twist and turn about their axis, each one of the four wings being able to beat independently, powered by very strong flight muscles, which switch “on” the moment the feet leave a perch. Their long bodies are arranged in slanting sections so as to absorb the shock of an impact when they wham into an unsuspecting victim. Flight speeds can touch almost 55 kmph, cruising speeds are more relaxed.  Their jaws make short work of their prey. They will take down flying insects like mosquitoes and flies (one famous dragonfly is said to have consumed 40 flies in two hours!) and, dragons will not spare damsels – or even each other for that matter. They are strongly territorial and fiercely protect their airspace (I have been charged by one) driving out or preferably eating trespassers (I was spared). Those glistening stained cellophane wings can twist and turn about their axis, enabling the dragonfly to dart hither and thither in a trice as well as hover and fly backwards. Their evocative daisy-chain flight mode while mating may look romantic but a dragon dude is anything but: roughly grabbing his ladylove with his claspers (sometimes causing injury) and hitching her to him, as she arches the tip of her body into his ‘sperm bag’ located on his abdomen. He will, however, gallantly escort her to where she lays her eggs but only to ensure that no other dude tries any hanky panky before that!

First published on: 05-10-2022 at 11:39:38 am
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