Flying insects can often
prove to be a nuisance — mosquito bites cause an itchy rash, a wasp’s sting
inflicts acute pain, flies are singularly disgusting, but dragonflies, with
their strange droning noise as they descend on to water, are harmless, with an almost
fairy-like appearance and movement. Their flight is so unique that engineers
have been inspired to design robots that will fly like them.
These insects have four
independent, alternately moving wings and they can fly at speeds of 60 mph.
They can shoot up in a perpendicular direction of 20 feet. An amazing
observation was recorded by a marine biologist Charles Anderson, who lives and
works in the Maldives. In a video-film, Dr Anderson carefully tracked
plain-coloured dragonflies, the Globe Skimmer (Pantala flavescens), only to
discover they make the longest migratory journey of any insect in the world,
flying a distance of 11,000 miles, back and forth, across the Indian Ocean.
Dragonflies, with their
delicately fluttering wings, intriguing flight movements and possessing
individual beauty, are precious creatures that indicate the health of the
environment. Zoologist David Attenborough described how these creatures came
into being 300 million years ago in his book, Life on Earth, when our planet’;s
vegetation was devoid of trees. Short grasses and shrubs covered the earth back
then and insects like dragonflies and crickets adapted to the subterranean
depths. Therefore, they moulted, shedding their skins as they grew. This form
of shedding skin still occurs with the larvae of the dragonfly.
It was only later, when
forests and waterbodies developed, that dragonflies and erstwhile ground
insects moved to trees or ponds and rivers. In fact, scientists have theorised
that oxygen levels during prehistoric times were about 50 per cent more than it
is today. That explained why dragonflies were larger in size at the time. They
grew smaller over millennia due to predation caused by prehistoric birds, some
of which were big. The ancient dragonfly certainly deserves more respect than
we give them, with humankind destroying their habitats.
Both dragonflies and
another species related to them, damselflies, require clean water to survive.
The aquatic habitats where their larvae hatch and develop will reflect on the
condition of the water, depending on whether these insects survive. If
waterbodies are contaminated by pesticides or sewage, the larvae will perish soon
enough. The fact that dragonflies consume mosquitoes proves how beneficial the
insects are to human health. From their ancient giant forms to the present day
dainty creatures, dragonflies, by their presence, give us hope of a
pollutant-free ecology. To sight these insects in large numbers will indicate
that water sources are clean and free from impurities.
It may be prudent to
check the status of dragonflies in India, to the extent possible. Let us focus
on two states: areas in Assam/Meghalaya and a zone in Bengal. A pilot study was
conducted to examine the diversity and distribution of dragonflies from
selected sites in Asansol and the Durgapur industrial area of Burdwan district,
from January 2012 to December 2015. A total of 57 different species was recorded,
writes Amar Kumar Nayak. Despite Asansol and Durgapur being an industrial belt,
the study revealed an encouraging number of dragonflies, in terms of diversity.
The region has wetlands, grasslands and ponds, making it a conducive zone for
dragonflies to flourish. In India, a total of about 500 species of dragonflies
has been recorded.
In Meghalaya 33
species were recorded. Bidyut Kumar Das and Sarma Uddipta, students of zoology,
had conducted a study of dragonflies in Assam’s wetlands in Barpeta district,
recording 23 species. Although studies on dragonflies in India have been
documented from the time of Linnaeus, in the 1850s, not much research was done
on the diversity of these insects in Assam. Empirical studies require concerted
efforts to check the status of dragonflies throughout Assam’s vast expanses.
According to Fraser (1933), “Life in the tropics would soon become unbearable
were it not for the vast numbers of dragonflies acting as scavengers of the
atmosphere.”
Incredibly, scientists
have discovered more than 5,000 species of dragonflies all over the world, with
450 species in North America alone. Dragonflies belong to the insect order
Odonata, from the Greek word meaning “the toothed one”. This refers to the
serrated teeth that are the insect’s mandibles. Their movable heads have large
hemispherical eyes that enable them to locate prey with remarkable vision. They
defend their territories by a pattern of patrolling, at various heights. Their
larvae are aquatic while the adults are predominantly terrestrial.
From 300 million years
ago to the present incorporates the incredible odyssey of the dragonfly, which
once upon a time lived in a world with no forests; and then the gradual shift
to a combination of terrestrial existence and an aquatic life, flying around
the earth and across its oceans.
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