Thames & Kosmos TK2 Scope, Experiment Manual

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The goliath walking stick (Eurycnema goliath)
grows to more than 30 cm in length.
Wing of a house fly
Sizing Up Insects
Insects are by far the most successful
group of animals in the world. There is
almost no living space that they have
not occupied since their emergence
about 300 to 400 million years ago.
From the snow- and ice-covered Hima-
layas to the hot, dry deserts of Africa,
from the Antarctic with temperatures
of below -35 °C to the open sea to 50
°C hot springs, a tremendous variety of
insects has exploited living spaces ev-
erywhere. Of the 1.4 million animal species
known today, 1 million of them are insects, and
insect researchers suspect that there are another 1 million
“new” species waiting to be discovered. It is truly an animal
group of superlatives.
And yet no insects are known to be much more than 30 cm
long (the stick insect Pharnacia serratipes reaches a body
length of 33 cm!). Why is it, that such successful animals are
generally no bigger than a few centimeters?
It could be said that their success is often a result of their small size. Insects are
often capable, precisely because of their tiny size, of making use of living spaces
that would be unavailable to them if they were larger. For example, the parasitic
Trichogramma wasps are so tiny (one of the largest species of that genus has a
wing span of 3 mm!) that their larvae are able to grow in the eggs of other insects.
But there are other reasons for why larger species of insect have not developed
over millions of years. In looking at the wings of many insects, probably the most
important reason for this becomes clear.
Delicate lines run through the filigree wings of insects: the wing veins. In some
insect orders such as the butterflies, for example, these are only covered by scales.
The name already gives away a bit of what task these “veins” are charged with.
You know that all animals need oxygen to survive. The land vertebrates have
lungs for this purpose. Aquatic animals such as fish get the oxygen they need from
the water with the aid of their gills. Once the oxygen has been breathed in, it is
transported by a special bodily fluid — the blood — and distributed throughout
the body.
The insects have developed a completely different principle for supplying their
bodies with oxygen. If you look at the sides of the rear body of an insect using a
magnifying glass, you will see tiny little dots. These dots, called stigmas, are actu-
ally little holes through which fresh air gets into the insect’s body. Starting at these
stigmas, a richly branched system of tubes extends through the entire insect body,
even into the wings. The wing veins are thus a component of the fresh air sup-
ply system in insects. The distribution of oxygen in the blood of larger animals is
possible because the blood is constantly pumped through the body by the heart.
Insects don’t have such a pump system. While the circulation of air in the tubes is
supported by bodily movements, this principle is not sufficient for transport over
The Vast Kingdom of
the Insects
9
Did You Know?
Many species of insect can only
be distinguished based on their
wings. Some insects are so similar
to each other that the pattern and
appearance of the veins in their
wings have to be used as the sole
distinguishing feature.
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