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FORAGING BEHAVIOUR OF DRAGONFLY ADULT AND LARVAE

Presented by: Awais nazir

Roll No: 33

Supervisor : Dr. Azhar Abbas Khan Baloch

Subject : Insect Ecology

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INTRODUCTION

A dragonfly is an insect belonging to the order Odonata

Consist of short bristly antennae, compound

eye composed of nearly 30,000 lenses, thorax is in the

center for locomotion, head is a tough, rounded capsule,

chewing mouth part

Incomplete Metamorphosis (Egg, Nymph, Adult)

3Fig 1: Metamorphosis Stage Fig 2: Adult Dragon Fly

BIOLOGY OF DRAGONFLY LARVAE During all stages of their lives, dragonflies are fearsome

and efficient hunters

If dragonfly larvae were eight to sixteen inches long, as

they probably were 300 million years ago, we would dare

not swim in fresh water for fear of being attacked

Any moving, living thing could be prey for dragonfly

larvae, including other dragonfly larvae, daphnia,

mosquito larvae, tadpoles and even small fish

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Fig 3: Dragonfly with

Labeling

BIOLOGY OF DRAGONFLY LARVAE

Aquatic larvae are very visual; any nearby movement is

noticed.

Their antennae are very sensitive and are used as tactile

sensors, picking up even slight movement.

Prey is secured primarily through the use of the

powerful, extendable lower lip (labium) that is equipped

with “teeth.”

In as little as 1/100 of a second, the labium can be

extended out to 1/3 the length of its body, snagging the

victim with the teeth and delivering it to the waiting jaws

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Fig 4: Dragonfly Larva catching prey

FORAGING BEHAVIOR OF DRAGONFLY LARVAE

Some dragonfly larvae, such as the darners, stalk their prey

among the plants and detritus of their underwater jungle

These “crawlers” are able to see a moving target from a

distance of several inches and will slowly pursue prey in a

cat-like manner until within striking distance

Other larvae, such as the emeralds, skimmers and the long-

legged cruisers, are “sprawlers,” blending into the bottom

materials with camouflaging markings or by a build up of silt

on body hairs

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Fig 5: Dragonfly Larva catching prey

FORAGING BEHAVIOR OF DRAGONFLY

LARVAE

Sprawlers lay in wait with their antennae laid out on the

muck or sand until suitable prey happens by

A third hunting style is demonstrated by the “burrowers.”

Most clubtails

spike tails are burrowers who disappear below the sand

or silt, only their eyes and the tips of their abdomens are

visible.

They lunge at anything that comes within striking

distance

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Fig 6: Sprawlers

FORAGING BEHAVIOR OF DRAGONFLY LARVAE

Despite their skill as predators, the larvae are also heavily

preyed upon by fish, birds, predatory aquatic insects and

other dragonfly nymphs

Larval gills are located inside their abdomen and water must

be pulled in through the rectum and expelled for them to

breathe

To avoid predators they accelerate this process and

effectively become “jet propelled.”

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Fig 7: Dragonfly Larvae Feeding on Tedpole

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Fig 8: Dragonfly Larvae Feeding on Alevin (Aquatic Fish)12

FORAGING BEHAVIOR OF DRAGONFLY ADULT

Adults are also fearsome predators that have even beenknown to take down a hummingbird

Their hunting prowess is due in no small part to largeeyes, resilient and maneuverable wings, spiky legs thatform a snagging net and a powerful, muscular thoraxserving both the wings and the legs

Adult dragonflies capture exclusively live prey andalmost always while they are on the wing

Flying insects are located visually and smaller prey iscaught directly by the mouth

Larger insects are snared in a basket that the dragonflyforms with its legs, transferring the food to its mouth afterit has been secured

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FORAGING BEHAVIOR OF DRAGONFLY ADULT

Prey is either eaten on the wing or from a perch

The hard parts of beetles and wings of butterflies, moths,

damselflies and other larger insects are discarded and

may be found below a favored perch by the observant

naturalist

If you can approach close enough to a chewing

dragonfly you will be able to hear them “crunch, crunch”

on the exoskeleton of their “McBug” sandwich.

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Fig 9 :Dragonfly Adult Feeding on Grass/Plant15

Fig 10: Dragonfly Adult Feeding an Insect

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TEMPERATURE CONTROL

Because warmth is needed for activity and an efficient

metabolism, most dragonflies disappear to protected

perches on cool days or when the sun disappears behind a

cloud

Despite the fact that insects are “cold blooded,” many

dragonflies maintain an internal temperature as high as 110

degrees F.

This is accomplished by the burning of calories during

physical exertion and by staying in the sun

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TEMPERATURE CONTROL

A cold dragonfly preparing to get the day started will shiver

its wings to create heat in its thorax until it has warmed itself

enough to take flight

Some dragonflies, such as the Ebony Bog haunter, Stygian

Shadow dragon and the blue darners have adapted to

cooler weather

as a method of allowing early- or late-season emergence or

to take advantage of the plethora of insect life that becomes

active at dusk

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TEMPERATURE CONTROL

In hot, sunny weather it is important that dragonflies don’t

overheat

Cooling strategies include becoming less active, moving into

shade and changing their body position

The obelisk position orients the dragonfly’s abdomen

directly at the sun, thereby reducing the surface area

exposed to solar heating

Some dragonflies also point their wings forward and down in

order to reduce exposure to sunlight and, perhaps, to reflect

light and heat away from their bodies.

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TEMPERATURE CONTROL

Dragonflies drink by thrusting their bodies down onto the

water’s surface in a sequence of one to three splashdowns

Water is absorbed through the exoskeleton

Dew is also absorbed on cool mornings.

Some species will be seen flying well after sunset on

moonlit evenings or under street lights

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MIGRATION

Certain species of dragonfly migrate, either en masse or

individually

Dragonflies follow weather fronts, fleeing cold fronts in

the fall on their way south and chasing warm fronts in the

spring when moving north

Another seasonal migrator is the Variegated Meadow

hawk who may be seen in early spring returning from

year-round haunts in Oklahoma or Texas

It is risky business though, as April snow and cold can

strand and freeze thousands.

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WINTERING

Most winter beneath the ice in the larval form in a state of

diapauses, which is a sort of suspended animation

Other species, such as some of the meadow hawks, lay

their eggs along shorelines where the eggs will sit through

the winter until high water in spring washes them into the

lake

22Fig 11: Meadow Hawks ( Dragonfly Species)

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