Experiments with water (more
about water? click here /
more about air click there
German
a morning with a children group of Eichberg
Primary School Lauterbach at 19.06. 2008
1.
Investigation of Lauter a small stream close to the school
Flowing water is the habitat of
different animals. Probably you will only find small ones:
Mayflies
are born in the Lauter from eggs. The females have only a short life.
After a very short time ashore they return to the water:
Underside a stone they fix hundreds of small eggs. After months a baby
mayfly (called larva) is hatching from each egg. In
spite of their small size they resemble mayflies. During their whole
underwater life the larvae are distinctive in that they breath
through 7 pairs of gills at both sides of their belly (abdomen). 3 tails
can be seen at its end. Like other insects
they have 6
legs at their breast (thorax)
and two big eyes aside their head.
The larvae feed on algae and grow quickly. After a short time their
hard skin is too small for them. Below the outer skin a soft skin is
growing. The outer skin cracks and the larva leaves it. 
Now it is
growing again and soon the second skin is also too small. It bursts as
a third soft skin has been formed. When the larva has reached its final
size
it has to leave the water and the female or male mayfly is hatching.
Larvae (of
one species in the Lauter) can be seen on the first photo and on the sketch at ist side: This
larva is flat and streamlined. Therefore it cannot be drifted off even
when the Lauter is in flood.
In the Lauter you will find
another species of mayflies that have not this streamlined shape.
In the
Lauter you will also find larvae of caddisflies. Most
of them are underwater architects: They build a house from small stones
or other
materials (left 
photo). Another species
also present in the Lauter does not have such a house (right ): Like mayfly larvae
they a head with eyes, a thorax with 3 pairs of legs and an abdomen
with 7 pairs of gills.
Larvae of caddisflies hatching from eggs are also growing, changing
their skin. When they have reached their final size they close their
house or build one to transform in a male or a female caddisfly that
leaves the water. They resemble small butterflies. In
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Stonefly larva
/ its last skin /
male / female with
male / with parcel of eggs
Stoneflies have their name because
they live under stones escaping light and current.
The species on the
photos lives in
the Lauter close to the fountain. In this habitat the water is cold
all the year. So it can dissolve more air than the water close to
your school. These larvae have no gills. So they suffer from lack
of air (click for
video). Before
transforming into a male (small, only stumps of wings) or a female
(Photo 3 and 4) they
have a length of 2 - 3 cm. The stonefly larvae you might find are much
smaller.
2.
Experiment with cold water
You need the ampoule you have
prepared at home.
a) Transfer as much
cold water to it as possible.
b) Cover the bottom of a small container (beaker of a tea candle) with
water. Leave it at a warm place.
c) Turn the ampoule with water slowly
upside down.
d) Place it in the container.
e) Wait for some hours. Changes?
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first publication: 18.06.2008
last modification: 23.06.08