Odonata
is the order of insects that includes dragonflies and damselflies. To the human
eye, their shining colors and delicate-looking wings make them beautiful
creatures to behold. In the natural world, however, they are fearsome predators.
Dragonflies and damselflies get their name from the powerful serrated jaws they
use to tear apart their prey. The word odonata means "toothed jaw."
Dragonflies
and damselflies are often confused with each other because they are very
similar. Close observation reveals the differences between them. The most
obvious difference is the way they hold their wings while at rest. Dragonflies
hold their wings out to the side while damselflies fold their wings back.
Dragonflies have very large eyes that seem to cover the entire face because
they are so close together that they touch each other. Damselflies' eyes are
smaller, and there is a space between them. Dragonflies are larger and stronger
animals than damselflies and fly longer distances. Thus, they can be found in
woods and fields away from the water. Damselflies are not such strong fliers
and are most often seen around the edges of ponds and streams since they do not
normally fly far from the water.
The
largest odonata living today are the Hawaiian endemic dragonfly and the Central
American damselfly, each of these species having a wingspan of 19 centimeters.
The smallest is the libellulid dragonfly, native to east Asia, with a wingspan
of just 20 millimeters. Fossils have been discovered that prove that dragonflies
have been in existence for over 300 million years. The largest dragonfly fossil
ever found belongs to the now-extinct meganeura monyi, which lived 300 million
years ago and had a wingspan of 75 centimeters. This giant was a fearsome predator
indeed, which feasted on small amphibians as well as on other insects.
Dragonflies
and damselflies both lay their eggs on or just below the surface of the water
in a pond or stream. Some species lay their eggs on the stem of an aquatic
plant. The babies emerge from the eggs in the form of nymphs. They live
underwater, breathing through gills and preying upon water insects, tadpoles,
small fish, and even other nymphs. They hunt by hiding in the shadows at the
bottom of a pond or stream, waiting for prey animals to swim by. They have a
special lip that they can extend far forward in order to grab their prey when
it comes close. Depending on the species, they live this way for several months
or even several years. As the nymph grows, it sheds its skin several times.
Finally, leaves the water and sheds its skin one last time. The adult emerges,
ready to live the next few weeks or months on land and in the air. The adults
do not live for more than four months, and many species live as adults for only
a few weeks.
The
exceptional visual abilities and flying skills of dragonflies and damselflies
make them very adept hunters. Their special eyes give them a nearly 360-degree
field of vision, and they can detect even the smallest movement or flash of
light caused by other flying insects. They have two sets of wings that can move
independently of each other. This gives them great maneuverability1 in the air,
which is important to these creatures because they catch their prey while
flying. They can hover, make sharp turns, and fly backward. Some species of
dragonflies can fly 60 kilometers an hour or more. Their prey consists of
flying insects such as mosquitoes, deerflies, smaller dragonflies, and
butterflies and moths. One species of dragonfly takes spiders out of their
webs.
Bloodthirsty
predators that they are, dragonflies and damselflies are prey for other animals
in their turn. The nymphs are eaten by fish, frogs, toads, and other aquatic
creatures. In the adult stage, they are hunted by birds, frogs, and larger
dragonflies and damselflies. They might also be caught in a spider's web. What
goes around comes around.
Questions 1 – 6
Which of the facts below
are true of dragonflies, and which are true of damselflies, according to the
information in the passage? On lines 1 – 6 on your answer sheet, write:
A if it is a fact about dragonflies only
B if it is a fact about damselflies only
C if it is a fact about both dragonflies and
damselflies
1
They have sawlike jaws.
2
They hold their wings on their backs while resting.
3
Their eyes have a gap between them.
4 They
can be seen in fields at a distance from ponds and streams.
5
The largest species has a wingspan of 19 centimeters.
6
The largest fossil has a wingspan of 75 centimeters.
Questions 7 – 13
Complete the notes about
the life cycle of odonata below. Choose your answers from the box below and
write the correct letters, A – K,
on lines 7 – 13
on your answer sheet.
The eggs are laid 7........................... The young
dragonflies and damselflies, called
8.........................
live
underwater for a few 9........................They
eat small water animals, catching their food 10..............................When they are almost fully grown, they leave
the water. The adults live for only a few 11............................
They are skillful' 12.........................
and catch their prey
13.............................
A in
the air E near
the water's surface I weeks
or months
B with
their lips F nymphs J
swimmers
C tadpoles G at
the bottom of a pond K with
their wings
D fliers H months
or years