DRAGONFLYS
DRAGONFLYS
With a superbly adapted body plan and behaviour repertoire that has stood the test of time.
The earliest fossil specimens date back 300 million years,
and in their form are virtually indistinguishable from their modern day counterparts.
The secret of their survival lies perhaps in the ecological niche that dragonflies occupy.
Dragonflies are intimately connected with fresh water ecosystems
and it's the strategies and adaptations that dragonflies employ at each phase of their life cycle
that make them such a success in this habitat.
Well Oat is usually the brightly coloured aerial hunter that we think of.
This phase of the dragonflies' life cycle forms only a small proportion of their life,
often less than a month in a total lifespan
that may be two to three years.
For the majority of their life, a dragonfly exists as a nymph.
A fully aquatic predator,
superbly adapted to exploit the abundance of food available in freshwater ecosystems.
Several species often share the same habitat
and have adopted a range of strategies enabling them to co-exist.
Many of the larger hawker nymphs are active predators,
openly moving through the aquatic vegetation stalking prey,
whereas chaser nymphs have specialised as ambush predators,
burying themselves in the sediment and waiting for prey to come to them.
The smaller and more vulnerable damselfly nymphs rely on concealment,
for much of the time remaining sedentary
and coloured to merge with the surrounding vegetation.
Although their lifestyles may vary,
all nymphs come equipped to hunt,
with large compound eyes and an extendable lower jaw
that they can project out like a hydraulic ram.
They are a formidable predator.
The nymphs are indiscriminate and voracious hunters
and are not averse to cannibalism.
Size matters in this world,
so even the nymphs of the largest dragonflies
need luck to survive the first few months of their lives
when their diminutive size exposes them to predation by larger nymphs.
If the nymph survives the hazards of its early life,
it must overcome the limitation placed on it
by its rigid exoskeleton in order to grow,
and this is achieved through a series of mounts.
Once free of the old exoskeleton,
the nymph puts on an instantaneous growth spurt
while the new exoskeleton is still supple.
After an hour or two it will harden
and no further growth will occur until the next malt.
The nymph looks almost ghost like
immediately after casting its old skin
and behaves cautiously as it will remain
vulnerable while the new exoskeleton hardens.
Malting punctuates distinct phases of growth for the nymphs
and these are known as instars
and may be repeated up to 15 or more times
before the nymph is finally ready to leave the water.
After two and a half years living below the surface,
the nymph is ready to undertake a final malt
that will see it leaving its aquatic home
and embarking on a final journey
to pass on its genes to the next generation.
Just before dawn, on a warm July day,
the nymph climbs up a reed stem
and sits motionless.
A few minutes later,
the carapace above the thorax begins to split
and the dragonfly begins to ease itself out
of the nymph's exoskeleton.
The dragonfly waits as its legs harden enough
for it to support itself.
As it re-orientates itself
and begins the slow process of unfolding its wings,
the dragonfly flexes,
stretching the still suple exoskeleton,
steadily elongating and expanding
to reach its full adult size.
Once the wings are fully extended,
the powerful muscles in the dragon's thorax
re-orient the wings into their final
horizontal position.
The dragonfly is now almost ready
to take its maiden flight.
Tremors in the flight muscle
are the first sign of impending departure.
And finally,
twelve hours after emerging as a nymph
from below the surface of the pond,
the flight muscles burst into life
and the dragonfly floats up
into the afternoon's ensuring.
The pale and fragile dragonfly
must now find a quiet spot to roost,
while its exoskeleton hardens
and develops the rich kulski
in its final form.
In the spring sunshine,
a profusion of damselflies
accompany the first of the dragons
to emerge from the water.
And these are the chasers.
Chasers are easy to spot
with their broad tapering abdomens
and distinctive colour schemes.
This male four-spotted chaser
will spend most of his time
perched close to the water,
hunting and waiting for passing females.
Although he's territorial,
he can't compete for aggression
with his close relative,
Chasers.
The bright blue males are fiercely territorial
and competition at the best mating pools
is fierce and unremitting.
The males engage in spectacular dogfights
in attempt to keep all the males away
from the favoured pool.
They perch close to the water,
ready to dart into the air
and drive away arrive,
or grab a passing female.
Mating only lasts a few seconds
before they break apart
and the female heads for the margins of the pond,
where she will begin laying
almost immediately,
dipping the tip of her abdomen in water
and scattering her eggs.
While the female lays her eggs,
the male hovers close by
to prevent her from being grabbed
by another male before she's finished of depositing.
There's no time for sentimentality here
and this female will mate with many males
and lay many hundreds of eggs
in the few short weeks of her animal life.
As spring moves into early summer,
a steady stream of colourful combatants
will arrive at the mating pools.
The female is the largest dragonfly in Britain.
And the black dart,
smaller than many damselflies,
is Britain's smallest.
In contrast to the chasers,
mating for many of the later emerging dragonflies
is carried out in less of a rush.
The male takes hold of the female behind the head.
The male has already transferred his sperm
from the tip of the abdomen
to a secondary sexual organ
situated on the underside of his abdomen
at the base of the legs.
And as the female curls her abdomen
in response to the male's grip,
the sexual organs come into contact
and fertilisation takes place.
Dartas remain attached during the process of egg laying.
This is a useful strategy for the male,
ensuring that the female isn't hijacked by another male
before she's completed laying.
It also seems an effective way of scattering eggs.
The male seeming to swing the female
to and fro as she deposits her eggs.
Hawke has taken altogether different approach to egg laying.
After fertilisation,
the females become almost secretive,
searching for suitable locations to lay their eggs
in the marginal vegetation at the edge of the pond.
This female appears to be concentrating intently
as she places individual eggs
into the rotting stems and vegetation.
Female hawkers are equipped with a sickle-shaped appendage
and this even enables them
to drill into rotting wood to place eggs.
The females lay in a wide variety of locations,
maximising the chances
that some of these eggs will hatch successfully.
It may seem somewhat random,
but it's worth remembering
that this pattern of behaviour is tried and tested
through countless generations.
By mid-october,
the pools that were alive with dragonflies
a few weeks before are now quiet.
The odd male hawker still remains,
but the few that have lasted this long
will soon succumb.
And either fall into the water
or fall prey to another predator
looking for a meal.
It's the end of the dragonfly's breeding season,
but down below the surface of the pond
there are dragons alive and well
and looking for a meal.
