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UNIT 1
5
Reading Passage
10
15
20
20
25
Listening
There are more than 37,000 known species of spiders in the world in a wide variety of shape's
and sizes! The largest spiders in the world live in the rain forests of South America and are known
by the people who live there as the "bird-eating spiders." These spiders can grow up to 28
centimeters in length- about the size of a dinner plate, and, as their name suggests, have been
known to eat small birds. In comparison, the smallest species of spider in the world is native to
Western Samoa. These tiny spiders are less than half a millimeter long — about the size of a period
on this page and live in plants that grow on mountain rocks.
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Some people like to keep spiders as pets, particularly tarantulas, which are native to North America
and can live for up to twenty-five years, Most people, on the other hand, do not like touching
spiders, and a significant number of people are afraid of them, mainly because of their poison.
However, despite their bad reputation, only thirty of the 37,000 known species of spiders are
deadly to humans. Spiders actually provide benefits to humans, by catching and eating harmful
insects such as flies and mosquitoes.
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The main thing that makes spiders different from other animals is that they spin web's to catch the
small insects they feed on. The unique silk of a spider's web is produced by special organs found
spider web is five times
in the lower part of the spider's body. It is light, elastic, and strong
stronger than steel. Additionally, it is completely biodegradable. This means that the web will
making it perfect for uses
completely decompose¹ and eventually return to nature over time
such as making fishing nets. Some people have tried to raise spiders commercially in order to
collect the silk these spiders produce, but no one has ever really managed to make a go of it. One
reason why these businesses never stand a chance is because it takes 670,000 spiders to produce
half a kilogram of silk, and all of these spiders need living insects for their food. In addition, spiders
are usually solitary² animals, and need to be kept alone.
Researchers at an American company working together with two U.S. universities may have found
a solution to making artificial spider web. Using genetically modified silkworms,³ the company
hopes that in the long run it will be able to make large quantities of very light, very strong fiber
for medical as well as other uses. Additionally, because the manufacture of the artificial web is from
living silkworms, the industry potentially would be non-polluting and less harmful to
the environment
