THE DRAGON-FLY
What child is there that is not familiar with the insect commonly known
as the dragon-fly, snake doctor or snake feeder? Every lover of the
stream or pond has seen these miniature aeroplanes darting now here, now
there but ever retracing their airy flight along the water's edge or
dipping in a sudden nose dive to skim its very surface. At times it is
seen to rest lazily, wings out-stretched, perched on some projecting
reed or other object. But when approached how suddenly it "takes off"
and is out of reach. The dragon-fly is an almost perfect model of the
modern monoplane. Its two long wings on either side are the planes, its
head the nose, its thorax the fuselage and its long projecting abdomen
the tail or rudder. On wing the dragon-fly is one of the swiftest and
most powerful insects. The dragon-flies are found all over the world
being most abundant in the warmer regions where rainfall and bodies of
water are abundant. For breeding they require water, their immature
stages living under water feeding on aquatic animal life. Our present
order of dragon-flies is the remains of an ancient race of insects of
immense size. From fossil remains we learn that ancient dragon-flies
had a wing expanse of three feet.
[Illustration: Cast off skin of dragon-fly nymph, showing shape and
position taken on a twig when the adult winged form emerged from the
last nymph stage.]
The dragon-fly is a beneficial insect thruout life. The young feed on
mosquito wigglers and similar life in ponds and streams while the adults
dart here and there over ponds, fields or lawn catching mosquitoes and
other winged insects. Many look upon the dragon-fly as a dangerous
stinging insect but it is entirely harmless and can be handled without
the least danger. They vary greatly in size and appearance. The
so-called damsel-flies form a group of dragon-flies or Odonata which
rest with the wings in a vertical position and the young aquatic stages
are more slender. In color markings dragon-flies include all hues of the
rainbow tho as a rule they do not have such extravagant colors as the
butterflies.
[Illustration: One of our common dragon-flies found about ponds and
streams.]
OBSERVATIONS AND FIELD STUDIES
Go into the fields and study and collect the different kinds of
dragon-flies and their young stages from the bottoms of ponds. How
swiftly can they fly? Do they fly high in the air as well as near the
water or surface of the earth? Can you see them catch other insects? Do
birds catch them and eat them? Take a position along the edge of a pond
and as they come flying by swing swiftly with your net and catch one.
Examine it carefully. Note the strength of the long, slender wings with
their lace-like network of veins. Measure the distance across the back
from tip to tip of wings. Compare this with the length from tip of head
to the tip of the abdomen. Examine the head with its large compound eyes
and the chewing mouth parts. Note the strong thorax which is filled with
muscles to operate the wings in flight. How many segments are there to
the abdomen?
With the hands or with a bucket dip up a quantity of mud and trash from
the bottom of a pond and pile it on the bank. As the water soaks away
watch for signs of life in the mass. If you find a few small creatures,
say half an inch long with large head and eyes, broad body and with six
rather long legs they are probably the nymph stages of dragon-flies.
Wash the mud off of them so that you can examine them carefully. With a
straw probe in the mouth and you will find that the lower lip is a long
elbowed structure which can be suddenly thrown out in front of it and
with a pair of pincher-like prongs at the tip it can catch and hold its
prey. Some forms keep their bodies covered with mud so that they can
slowly creep up close to their prey.
Collect several nymphs and keep them in a jar of water and study their
movements and feeding habits. Disturb one with a pencil or straw and see
how it darts forward. It has a water chamber in the large intestines,
including also the respiratory tracheal gills, from which the water can
be suddenly squirted which throws the insect forward. The escaping
stream of water forces the insect forward on the same principle as the
rotating lawn sprinkler. If you collect some almost mature nymphs and
keep them for a time in a vessel of water you may see them crawl out of
the water, shed their skin and change to winged adults. Collect a few
adults of different species for pinning in your permanent collection.